diagnostics_hierarchy/

lib.rs

// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Diagnostics hierarchy
//!
//! This library provides a tree strcture used to store diagnostics data such as inspect and logs,
//! as well as utilities for reading from it, serializing and deserializing it and testing it.

use base64::display::Base64Display;
use fidl_fuchsia_diagnostics::{
    PropertySelector, Selector, StringSelector, StringSelectorUnknown, SubtreeSelector,
    TreeSelector,
};
use num_derive::{FromPrimitive, ToPrimitive};
use num_traits::bounds::Bounded;
use selectors::ValidateExt;
use serde::{Deserialize, Serialize};
use std::borrow::{Borrow, Cow};
use std::cmp::Ordering;
use std::collections::BTreeMap;
use std::fmt::{Display, Formatter, Result as FmtResult};
use std::ops::{Add, AddAssign, MulAssign};
use thiserror::Error;

pub mod macros;
pub mod serialization;

/// Format in which the array will be read.
///
/// Histograms are formatted with its parameters inline with its buckets:
///
/// - ...N parameters...
/// - underflow_bucket
/// - ...M buckets...
/// - overflow_bucket
///
/// Helper functions exist to make it easier to work with these formats:
///
/// - [`ArrayFormat::underflow_bucket_index`] returns the index of the underflow
///   bucket, which also happens to be the first bucket.
/// - [`ArrayFormat::extra_slots`] returns the number of additional slots
///   necessary to store parameters and underflow buckets.
///
#[derive(Copy, Clone, Debug, PartialEq, Eq, FromPrimitive, ToPrimitive)]
#[repr(u8)]
pub enum ArrayFormat {
    /// Regular array, it stores N values in N slots.
    Default = 0,

    /// The array is a linear histogram with N buckets and N+4 slots, which are:
    /// - param_floor_value
    /// - param_step_size
    /// - underflow_bucket
    /// - ...N buckets...
    /// - overflow_bucket
    LinearHistogram = 1,

    /// The array is an exponential histogram with N buckets and N+5 slots, which are:
    /// - param_floor_value
    /// - param_initial_step
    /// - param_step_multiplier
    /// - underflow_bucket
    /// - ...N buckets...
    /// - overflow_bucket
    ExponentialHistogram = 2,
}

impl ArrayFormat {
    /// Return index of the underflow bucket for histograms, or 0 if not a
    /// histogram.
    pub const fn underflow_bucket_index(self) -> usize {
        match self {
            ArrayFormat::Default => 0,
            ArrayFormat::LinearHistogram => 2,
            ArrayFormat::ExponentialHistogram => 3,
        }
    }

    /// Return index of the overflow bucket for histograms, or 0 if not a
    /// histogram. Depends on the number of buckets.
    pub const fn overflow_bucket_index(self, buckets: usize) -> usize {
        match self {
            ArrayFormat::Default => 0,
            ArrayFormat::LinearHistogram => self.extra_slots() + buckets - 1,
            ArrayFormat::ExponentialHistogram => self.extra_slots() + buckets - 1,
        }
    }

    /// Return count of extra slots needed for storing parameters and
    /// underflow/overflow slots.
    pub const fn extra_slots(self) -> usize {
        match self {
            // 0 parameters + 0 extra buckets
            ArrayFormat::Default => 0,
            // 2 parameters (floor, step size) + underflow bucket + overflow bucket
            ArrayFormat::LinearHistogram => 4,
            // 3 parameters (floor, initial step, step multiplier) + underflow bucket + overflow bucket
            ArrayFormat::ExponentialHistogram => 5,
        }
    }
}

/// A hierarchy of nodes representing structured data, such as Inspect or
/// structured log data.
///
/// Each hierarchy consists of properties, and a map of named child hierarchies.
#[derive(Clone, Debug, PartialEq)]
pub struct DiagnosticsHierarchy<Key = String> {
    /// The name of this node.
    pub name: String,

    /// The properties for the node.
    pub properties: Vec<Property<Key>>,

    /// The children of this node.
    pub children: Vec<DiagnosticsHierarchy<Key>>,

    /// Values that were impossible to load.
    pub missing: Vec<MissingValue>,
}

/// A value that couldn't be loaded in the hierarchy and the reason.
#[derive(Clone, Debug, PartialEq)]
pub struct MissingValue {
    /// Specific reason why the value couldn't be loaded.
    pub reason: MissingValueReason,

    /// The name of the value.
    pub name: String,
}

/// Reasons why the value couldn't be loaded.
#[derive(Clone, Debug, PartialEq)]
pub enum MissingValueReason {
    /// A referenced hierarchy in the link was not found.
    LinkNotFound,

    /// A linked hierarchy couldn't be parsed.
    LinkParseFailure,

    /// There was no attempt to read the link.
    LinkNeverExpanded,

    /// There was a timeout while reading.
    Timeout,
}

/// Compares the names of two properties or nodes. If both are unsigned integers, then it compares
/// their numerical value.
fn name_partial_cmp(a: &str, b: &str) -> Ordering {
    match (a.parse::<u64>(), b.parse::<u64>()) {
        (Ok(n), Ok(m)) => n.partial_cmp(&m).unwrap(),
        _ => a.partial_cmp(b).unwrap(),
    }
}

impl<Key> DiagnosticsHierarchy<Key>
where
    Key: AsRef<str>,
{
    /// Sorts the properties and children of the diagnostics hierarchy by name.
    pub fn sort(&mut self) {
        self.properties.sort_by(|p1, p2| name_partial_cmp(p1.name(), p2.name()));
        self.children.sort_by(|c1, c2| name_partial_cmp(&c1.name, &c2.name));
        for child in self.children.iter_mut() {
            child.sort();
        }
    }

    /// Creates a new empty diagnostics hierarchy with the root node named "root".
    pub fn new_root() -> Self {
        DiagnosticsHierarchy::new("root", vec![], vec![])
    }

    /// Creates a new diagnostics hierarchy with the given `name` for the root and the given
    /// `properties` and `children` under that root.
    pub fn new(
        name: impl Into<String>,
        properties: Vec<Property<Key>>,
        children: Vec<DiagnosticsHierarchy<Key>>,
    ) -> Self {
        Self { name: name.into(), properties, children, missing: vec![] }
    }

    /// Either returns an existing child of `self` with name `name` or creates
    /// a new child with name `name`.
    pub fn get_or_add_child_mut<T>(&mut self, name: T) -> &mut DiagnosticsHierarchy<Key>
    where
        T: AsRef<str>,
    {
        // We have to use indices to iterate here because the borrow checker cannot
        // deduce that there are no borrowed values in the else-branch.
        // TODO(https://fxbug.dev/42122598): We could make this cleaner by changing the DiagnosticsHierarchy
        // children to hashmaps.
        match (0..self.children.len()).find(|&i| self.children[i].name == name.as_ref()) {
            Some(matching_index) => &mut self.children[matching_index],
            None => {
                self.children.push(DiagnosticsHierarchy::new(name.as_ref(), vec![], vec![]));
                self.children
                    .last_mut()
                    .expect("We just added an entry so we cannot get None here.")
            }
        }
    }

    /// Add a child to this DiagnosticsHierarchy.
    ///
    /// Note: It is possible to create multiple children with the same name using this method, but
    /// readers may not support such a case.
    pub fn add_child(&mut self, insert: DiagnosticsHierarchy<Key>) {
        self.children.push(insert);
    }

    /// Creates and returns a new Node whose location in a hierarchy
    /// rooted at `self` is defined by node_path.
    ///
    /// Requires: that node_path is not empty.
    /// Requires: that node_path begin with the key fragment equal to the name of the node
    ///           that add is being called on.
    ///
    /// NOTE: Inspect VMOs may allow multiple nodes of the same name. In this case,
    ///        the first node found is returned.
    pub fn get_or_add_node<T>(&mut self, node_path: &[T]) -> &mut DiagnosticsHierarchy<Key>
    where
        T: AsRef<str>,
    {
        assert!(!node_path.is_empty());
        let mut iter = node_path.iter();
        let first_path_string = iter.next().unwrap().as_ref();
        // It is an invariant that the node path start with the key fragment equal to the
        // name of the node that get_or_add_node is called on.
        assert_eq!(first_path_string, &self.name);
        let mut curr_node = self;
        for node_path_entry in iter {
            curr_node = curr_node.get_or_add_child_mut(node_path_entry);
        }
        curr_node
    }

    /// Inserts a new Property into this hierarchy.
    pub fn add_property(&mut self, property: Property<Key>) {
        self.properties.push(property);
    }

    /// Inserts a new Property into a Node whose location in a hierarchy
    /// rooted at `self` is defined by node_path.
    ///
    /// Requires: that node_path is not empty.
    /// Requires: that node_path begin with the key fragment equal to the name of the node
    ///           that add is being called on.
    ///
    /// NOTE: Inspect VMOs may allow multiple nodes of the same name. In this case,
    ///       the property is added to the first node found.
    pub fn add_property_at_path<T>(&mut self, node_path: &[T], property: Property<Key>)
    where
        T: AsRef<str>,
    {
        self.get_or_add_node(node_path).properties.push(property);
    }

    /// Provides an iterator over the diagnostics hierarchy returning properties in pre-order.
    pub fn property_iter(&self) -> DiagnosticsHierarchyIterator<'_, Key, PropertyIter> {
        DiagnosticsHierarchyIterator::new(self)
    }

    pub fn error_iter(&self) -> DiagnosticsHierarchyIterator<'_, Key, ErrorIter> {
        DiagnosticsHierarchyIterator::new(self)
    }

    /// Adds a value that couldn't be read. This can happen when loading a lazy child.
    pub fn add_missing(&mut self, reason: MissingValueReason, name: String) {
        self.missing.push(MissingValue { reason, name });
    }
    /// Returns the property of the given |name| if one exists.
    pub fn get_property(&self, name: &str) -> Option<&Property<Key>> {
        self.properties.iter().find(|prop| prop.name() == name)
    }

    /// Returns the child of the given |name| if one exists.
    pub fn get_child(&self, name: &str) -> Option<&DiagnosticsHierarchy<Key>> {
        self.children.iter().find(|node| node.name == name)
    }

    /// Returns a mutable reference to the child of the given |name| if one exists.
    pub fn get_child_mut(&mut self, name: &str) -> Option<&mut DiagnosticsHierarchy<Key>> {
        self.children.iter_mut().find(|node| node.name == name)
    }

    /// Returns the child of the given |path| if one exists.
    pub fn get_child_by_path(&self, path: &[&str]) -> Option<&DiagnosticsHierarchy<Key>> {
        let mut result = Some(self);
        for name in path {
            result = result.and_then(|node| node.get_child(name));
        }
        result
    }

    /// Returns a mutable reference to the child of the given |path| if one exists.
    pub fn get_child_by_path_mut(
        &mut self,
        path: &[&str],
    ) -> Option<&mut DiagnosticsHierarchy<Key>> {
        let mut result = Some(self);
        for name in path {
            result = result.and_then(|node| node.get_child_mut(name));
        }
        result
    }

    /// Returns the property of the given |name| if one exists.
    pub fn get_property_by_path(&self, path: &[&str]) -> Option<&Property<Key>> {
        let node = self.get_child_by_path(&path[..path.len() - 1]);
        node.and_then(|node| node.get_property(path[path.len() - 1]))
    }
}

impl<Key> DiagnosticsHierarchy<Key>
where
    Key: PartialEq,
{
    /// Recursively merge another [`DiagnosticsHierarchy`] into this one.
    pub fn merge(&mut self, other: DiagnosticsHierarchy<Key>) {
        for other_property in other.properties {
            if let Some(existing) =
                self.properties.iter_mut().find(|p| p.key() == other_property.key())
            {
                *existing = other_property;
            } else {
                self.properties.push(other_property);
            }
        }

        for other_child in other.children {
            if let Some(existing_child) =
                self.children.iter_mut().find(|c| c.name == other_child.name)
            {
                existing_child.merge(other_child);
            } else {
                // Remove missing errors for matching lazy nodes.
                self.missing.retain(|m| m.name != other_child.name);

                self.children.push(other_child);
            }
        }

        for other_missing in other.missing {
            if !self.missing.contains(&other_missing) {
                self.missing.push(other_missing);
            }
        }
    }
}

macro_rules! property_type_getters_ref {
    ($([$variant:ident, $fn_name:ident, $type:ty]),*) => {
        paste::item! {
          impl<Key> Property<Key> {
              $(
                  #[doc = "Returns the " $variant " value or `None` if the property isn't of that type"]
                  pub fn $fn_name(&self) -> Option<&$type> {
                      match self {
                          Property::$variant(_, value) => Some(value),
                          _ => None,
                      }
                  }
              )*
          }
        }
    }
}

macro_rules! property_type_getters_copy {
    ($([$variant:ident, $fn_name:ident, $type:ty]),*) => {
        paste::item! {
          impl<Key> Property<Key> {
              $(
                  #[doc = "Returns the " $variant " value or `None` if the property isn't of that type"]
                  pub fn $fn_name(&self) -> Option<$type> {
                      match self {
                          Property::$variant(_, value) => Some(*value),
                          _ => None,
                      }
                  }
              )*
          }
        }
    }
}

property_type_getters_copy!(
    [Int, int, i64],
    [Uint, uint, u64],
    [Double, double, f64],
    [Bool, boolean, bool]
);

property_type_getters_ref!(
    [String, string, str],
    [Bytes, bytes, [u8]],
    [DoubleArray, double_array, ArrayContent<f64>],
    [IntArray, int_array, ArrayContent<i64>],
    [UintArray, uint_array, ArrayContent<u64>],
    [StringList, string_list, [String]]
);

struct WorkStackEntry<'a, Key> {
    node: &'a DiagnosticsHierarchy<Key>,
    key: Vec<&'a str>,
}

pub struct PropertyIter;
pub struct ErrorIter;

pub struct DiagnosticsHierarchyIterator<'a, Key, PropOrIterMarker> {
    work_stack: Vec<WorkStackEntry<'a, Key>>,
    current_key: Vec<&'a str>,
    current_node: Option<&'a DiagnosticsHierarchy<Key>>,
    current_index: usize,
    phantom: std::marker::PhantomData<PropOrIterMarker>,
}

enum EndOfTheLine<'a, T, Key> {
    Yes(Option<T>),
    No(&'a DiagnosticsHierarchy<Key>),
}

impl<'a, Key, Marker> DiagnosticsHierarchyIterator<'a, Key, Marker> {
    /// Creates a new iterator for the given `hierarchy`.
    fn new(hierarchy: &'a DiagnosticsHierarchy<Key>) -> Self {
        DiagnosticsHierarchyIterator {
            work_stack: vec![WorkStackEntry { node: hierarchy, key: vec![&hierarchy.name] }],
            current_key: vec![],
            current_node: None,
            current_index: 0,
            phantom: std::marker::PhantomData,
        }
    }

    /// Get the next node. This abstracts stack management away from the type being iterated over.
    fn get_node<T, U: 'a, F: FnOnce(&'a DiagnosticsHierarchy<Key>) -> &Vec<U>>(
        &mut self,
        iterable_node_data: F,
    ) -> EndOfTheLine<'a, (Vec<&'a str>, Option<&'a T>), Key> {
        match self.current_node {
            // If we are going through a node's data, that node will be set here.
            Some(node) => EndOfTheLine::No(node),
            None => {
                // If we don't have a node we are currently working with, then go to the next
                // node in our stack.
                let Some(WorkStackEntry { node, key }) = self.work_stack.pop() else {
                    return EndOfTheLine::Yes(None);
                };

                // Push to the stack all children of the new node.
                for child in node.children.iter() {
                    let mut child_key = key.clone();
                    child_key.push(&child.name);
                    self.work_stack.push(WorkStackEntry { node: child, key: child_key })
                }

                // If this node doesn't have any data we care about, we still want to return that it
                // exists, so we return with a None for data type we are examining.
                if iterable_node_data(node).is_empty() {
                    return EndOfTheLine::Yes(Some((key.clone(), None)));
                }

                self.current_index = 0;
                self.current_key = key;

                EndOfTheLine::No(node)
            }
        }
    }

    fn advance_index<T>(
        &mut self,
        data: &'a [T],
        new_current: &'a DiagnosticsHierarchy<Key>,
    ) -> &'a T {
        let datum = &data[self.current_index];
        self.current_index += 1;
        self.current_node = Some(new_current);
        datum
    }
}

impl<'a, Key> Iterator for DiagnosticsHierarchyIterator<'a, Key, PropertyIter> {
    /// Each item is a path to the node holding the resulting property.
    /// If a node has no properties, a `None` will be returned for it.
    /// If a node has properties a `Some` will be returned for each property and no `None` will be
    /// returned.
    type Item = (Vec<&'a str>, Option<&'a Property<Key>>);

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            let node = match self.get_node(|node| &node.properties) {
                EndOfTheLine::Yes(r) => return r,
                EndOfTheLine::No(n) => n,
            };

            // We were already done with this node. Try the next item in our stack.
            if self.current_index == node.properties.len() {
                self.current_node = None;
                continue;
            }

            // Return the current property and advance our index to the next node we want to
            // explore.
            let property = self.advance_index(&node.properties, node);

            return Some((self.current_key.clone(), Some(property)));
        }
    }
}

impl<'a, Key> Iterator for DiagnosticsHierarchyIterator<'a, Key, ErrorIter> {
    /// Each item is a path to the node with a missing link.
    /// If a node has no missing links, a `None` will be returned for it.
    /// If a node has missing links a `Some` will be returned for each link and no `None` will be
    /// returned.
    type Item = (Vec<&'a str>, Option<&'a MissingValue>);

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            let node = match self.get_node(|node| &node.missing) {
                EndOfTheLine::Yes(r) => return r,
                EndOfTheLine::No(n) => n,
            };

            // We were already done with this node. Try the next item in our stack.
            if self.current_index == node.missing.len() {
                self.current_node = None;
                continue;
            }

            // Return the current error and advance our index to the next node we want to
            // explore.
            let err = self.advance_index(&node.missing, node);
            return Some((self.current_key.clone(), Some(err)));
        }
    }
}

/// A named property. Each of the fields consists of (name, value).
///
/// Key is the type of the property's name and is typically a string. In cases where
/// there are well known, common property names, an alternative may be used to
/// reduce copies of the name.
#[derive(Debug, PartialEq, Clone)]
pub enum Property<Key = String> {
    /// The value is a string.
    String(Key, String),

    /// The value is a bytes vector.
    Bytes(Key, Vec<u8>),

    /// The value is an integer.
    Int(Key, i64),

    /// The value is an unsigned integer.
    Uint(Key, u64),

    /// The value is a double.
    Double(Key, f64),

    /// The value is a boolean.
    Bool(Key, bool),

    /// The value is a double array.
    DoubleArray(Key, ArrayContent<f64>),

    /// The value is an integer array.
    IntArray(Key, ArrayContent<i64>),

    /// The value is an unsigned integer array.
    UintArray(Key, ArrayContent<u64>),

    /// The value is a list of strings.
    StringList(Key, Vec<String>),
}

impl<K> Property<K> {
    /// Returns the key of a property
    pub fn key(&self) -> &K {
        match self {
            Property::String(k, _) => k,
            Property::Bytes(k, _) => k,
            Property::Int(k, _) => k,
            Property::Uint(k, _) => k,
            Property::Double(k, _) => k,
            Property::Bool(k, _) => k,
            Property::DoubleArray(k, _) => k,
            Property::IntArray(k, _) => k,
            Property::UintArray(k, _) => k,
            Property::StringList(k, _) => k,
        }
    }

    /// Returns a string indicating which variant of property this is, useful for printing
    /// debug values.
    pub fn discriminant_name(&self) -> &'static str {
        match self {
            Property::String(_, _) => "String",
            Property::Bytes(_, _) => "Bytes",
            Property::Int(_, _) => "Int",
            Property::IntArray(_, _) => "IntArray",
            Property::Uint(_, _) => "Uint",
            Property::UintArray(_, _) => "UintArray",
            Property::Double(_, _) => "Double",
            Property::DoubleArray(_, _) => "DoubleArray",
            Property::Bool(_, _) => "Bool",
            Property::StringList(_, _) => "StringList",
        }
    }

    /// Return a a numeric property as a signed integer. Useful for having a single function to call
    /// when a property has been passed through JSON, potentially losing its original signedness.
    ///
    /// Note: unsigned integers larger than `isize::MAX` will be returned as `None`. If you expect
    /// values that high, consider calling `Property::int()` and `Property::uint()` directly.
    pub fn number_as_int(&self) -> Option<i64> {
        match self {
            Property::Int(_, i) => Some(*i),
            Property::Uint(_, u) => i64::try_from(*u).ok(),
            Property::String(..)
            | Property::Bytes(..)
            | Property::Double(..)
            | Property::Bool(..)
            | Property::DoubleArray(..)
            | Property::IntArray(..)
            | Property::UintArray(..)
            | Property::StringList(..) => None,
        }
    }
}

impl<K> Display for Property<K>
where
    K: AsRef<str>,
{
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        macro_rules! pair {
            ($fmt:literal, $val:expr) => {
                write!(f, "{}={}", self.key().as_ref(), format_args!($fmt, $val))
            };
        }
        match self {
            Property::String(_, v) => pair!("{}", v),
            Property::Bytes(_, v) => {
                pair!("b64:{}", Base64Display::new(v, &base64::engine::general_purpose::STANDARD))
            }
            Property::Int(_, v) => pair!("{}", v),
            Property::Uint(_, v) => pair!("{}", v),
            Property::Double(_, v) => pair!("{}", v),
            Property::Bool(_, v) => pair!("{}", v),
            Property::DoubleArray(_, v) => pair!("{:?}", v),
            Property::IntArray(_, v) => pair!("{:?}", v),
            Property::UintArray(_, v) => pair!("{:?}", v),
            Property::StringList(_, v) => pair!("{:?}", v),
        }
    }
}

/// Errors that can happen in this library.
#[derive(Debug, Error)]
pub enum Error {
    #[error("Missing elements for {histogram_type:?} histogram. Expected {expected}, got {actual}")]
    MissingHistogramElements { histogram_type: ArrayFormat, expected: usize, actual: usize },

    #[error("TreeSelector only supports property and subtree selection.")]
    InvalidTreeSelector,

    #[error(transparent)]
    Selectors(#[from] selectors::Error),

    #[error(transparent)]
    InvalidSelector(#[from] selectors::ValidationError),
}

impl Error {
    fn missing_histogram_elements(histogram_type: ArrayFormat, actual: usize) -> Self {
        Self::MissingHistogramElements {
            histogram_type,
            actual,
            expected: histogram_type.extra_slots() + 1,
        }
    }
}

/// A linear histogram property.
#[cfg_attr(feature = "json_schema", derive(schemars::JsonSchema))]
#[derive(Debug, Serialize, Deserialize, PartialEq, Clone)]
pub struct LinearHistogram<T> {
    /// The number of buckets. If indexes is None this should equal counts.len().
    pub size: usize,

    /// The floor of the lowest bucket (not counting the negative-infinity bucket).
    pub floor: T,

    /// The increment for each bucket range.
    pub step: T,

    /// The number of items in each bucket.
    pub counts: Vec<T>,

    /// If Some<_>, the indexes of nonzero counts.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub indexes: Option<Vec<usize>>,
}

/// An exponential histogram property.
#[cfg_attr(feature = "json_schema", derive(schemars::JsonSchema))]
#[derive(Debug, Serialize, Deserialize, PartialEq, Clone)]
pub struct ExponentialHistogram<T> {
    /// The number of buckets. If indexes is None this should equal counts.len().
    pub size: usize,

    /// The floor of the lowest bucket (not counting the negative-infinity bucket).
    pub floor: T,

    /// The increment for the second floor.
    pub initial_step: T,

    /// The multiplier for each successive floor.
    pub step_multiplier: T,

    /// The number of items in each bucket.
    pub counts: Vec<T>,

    /// If Some<_>, the indexes of nonzero counts.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub indexes: Option<Vec<usize>>,
}

/// Represents the content of a DiagnosticsHierarchy array property: a regular array or a
/// linear/exponential histogram.
#[derive(Debug, PartialEq, Clone)]
pub enum ArrayContent<T> {
    /// The contents of an array.
    Values(Vec<T>),

    /// The data for a linear histogram.
    LinearHistogram(LinearHistogram<T>),

    // The data for an exponential histogram.
    ExponentialHistogram(ExponentialHistogram<T>),
}

impl<T> ArrayContent<T>
where
    T: Add<Output = T> + num_traits::Zero + AddAssign + Copy + MulAssign + PartialEq + Bounded,
{
    /// Creates a new ArrayContent parsing the `values` based on the given `format`.
    pub fn new(values: Vec<T>, format: ArrayFormat) -> Result<Self, Error> {
        let (counts, indexes) = match format {
            ArrayFormat::Default => return Ok(Self::Values(values)),
            ArrayFormat::LinearHistogram | ArrayFormat::ExponentialHistogram => {
                // Check that the minimum required values are available:
                // floor, step size, underflow, bucket 0, overflow
                if values.len() < format.extra_slots() + 1 {
                    return Err(Error::missing_histogram_elements(format, values.len()));
                }
                let buckets = &values[format.underflow_bucket_index()..];

                match serialization::maybe_condense_histogram(buckets, &None) {
                    None => (buckets.to_vec(), None),
                    Some((counts, indexes)) => (counts, Some(indexes)),
                }
            }
        };

        Ok(match format {
            ArrayFormat::Default => unreachable!(),
            ArrayFormat::LinearHistogram => Self::LinearHistogram(LinearHistogram {
                floor: values[0],
                step: values[1],
                counts,
                indexes,
                size: values.len() - 2,
            }),
            ArrayFormat::ExponentialHistogram => Self::ExponentialHistogram(ExponentialHistogram {
                floor: values[0],
                initial_step: values[1],
                step_multiplier: values[2],
                counts,
                indexes,
                size: values.len() - 3,
            }),
        })
    }

    /// Returns the number of items in the array.
    pub fn len(&self) -> usize {
        match self {
            Self::Values(vals) => vals.len(),
            Self::LinearHistogram(LinearHistogram { size, .. })
            | Self::ExponentialHistogram(ExponentialHistogram { size, .. }) => *size,
        }
    }

    /// Returns whether the array is empty or not.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Returns the raw values of this Array content. In the case of a histogram, returns the
    /// bucket counts.
    pub fn raw_values(&self) -> Cow<'_, Vec<T>> {
        match self {
            Self::Values(values) => Cow::Borrowed(values),
            Self::LinearHistogram(LinearHistogram { size, counts, indexes, .. })
            | Self::ExponentialHistogram(ExponentialHistogram { size, counts, indexes, .. }) => {
                if let Some(indexes) = indexes {
                    let mut values = vec![T::zero(); *size];
                    for (count, index) in counts.iter().zip(indexes.iter()) {
                        if index <= size {
                            values[*index] = *count;
                        }
                    }
                    Cow::Owned(values)
                } else {
                    Cow::Borrowed(counts)
                }
            }
        }
    }
}

pub mod testing {
    use crate::ArrayContent;
    use num_traits::bounds::Bounded;
    use std::ops::{Add, AddAssign, MulAssign};

    // Require test code to import CondensableOnDemand to access the
    // condense_histogram() associated function.
    pub trait CondensableOnDemand {
        fn condense_histogram(&mut self);
    }

    fn condense_counts<T: num_traits::Zero + Copy + PartialEq>(
        counts: &[T],
    ) -> (Vec<T>, Vec<usize>) {
        let mut condensed_counts = vec![];
        let mut indexes = vec![];
        for (index, count) in counts.iter().enumerate() {
            if *count != T::zero() {
                condensed_counts.push(*count);
                indexes.push(index);
            }
        }
        (condensed_counts, indexes)
    }

    impl<T> CondensableOnDemand for ArrayContent<T>
    where
        T: Add<Output = T> + num_traits::Zero + AddAssign + Copy + MulAssign + PartialEq + Bounded,
    {
        fn condense_histogram(&mut self) {
            match self {
                Self::Values(_) => (),
                Self::LinearHistogram(histogram) => {
                    if histogram.indexes.is_some() {
                        return;
                    }
                    let (counts, indexes) = condense_counts(&histogram.counts);
                    histogram.counts = counts;
                    histogram.indexes = Some(indexes);
                }
                Self::ExponentialHistogram(histogram) => {
                    if histogram.indexes.is_some() {
                        return;
                    }
                    let (counts, indexes) = condense_counts(&histogram.counts);
                    histogram.counts = counts;
                    histogram.indexes = Some(indexes);
                }
            }
        }
    }
}

impl<Key> Property<Key>
where
    Key: AsRef<str>,
{
    /// Returns the key of a property.
    pub fn name(&self) -> &str {
        match self {
            Property::String(name, _)
            | Property::Bytes(name, _)
            | Property::Int(name, _)
            | Property::IntArray(name, _)
            | Property::Uint(name, _)
            | Property::UintArray(name, _)
            | Property::Double(name, _)
            | Property::Bool(name, _)
            | Property::DoubleArray(name, _)
            | Property::StringList(name, _) => name.as_ref(),
        }
    }
}

impl<T: Borrow<Selector>> TryFrom<&[T]> for HierarchyMatcher {
    type Error = Error;

    fn try_from(selectors: &[T]) -> Result<Self, Self::Error> {
        // TODO(https://fxbug.dev/42069126: remove cloning, the archivist can probably hold
        // HierarchyMatcher<'static>
        let mut matcher = HierarchyMatcher::default();
        for selector in selectors {
            let selector = selector.borrow();
            selector.validate().map_err(|e| Error::Selectors(e.into()))?;

            // Safe to unwrap since we already validated the selector.
            // TODO(https://fxbug.dev/42069126): instead of doing this over Borrow<Selector> do it over
            // Selector.
            match selector.tree_selector.clone().unwrap() {
                TreeSelector::SubtreeSelector(subtree_selector) => {
                    matcher.insert_subtree(subtree_selector.clone());
                }
                TreeSelector::PropertySelector(property_selector) => {
                    matcher.insert_property(property_selector.clone());
                }
                _ => return Err(Error::Selectors(selectors::Error::InvalidTreeSelector)),
            }
        }
        Ok(matcher)
    }
}

impl<T: Borrow<Selector>> TryFrom<Vec<T>> for HierarchyMatcher {
    type Error = Error;

    fn try_from(selectors: Vec<T>) -> Result<Self, Self::Error> {
        selectors[..].try_into()
    }
}

#[derive(Debug)]
struct OrdStringSelector(StringSelector);

impl From<StringSelector> for OrdStringSelector {
    fn from(selector: StringSelector) -> Self {
        Self(selector)
    }
}

impl Ord for OrdStringSelector {
    fn cmp(&self, other: &OrdStringSelector) -> Ordering {
        match (&self.0, &other.0) {
            (StringSelector::ExactMatch(s), StringSelector::ExactMatch(o)) => s.cmp(o),
            (StringSelector::StringPattern(s), StringSelector::StringPattern(o)) => s.cmp(o),
            (StringSelector::ExactMatch(_), StringSelector::StringPattern(_)) => Ordering::Less,
            (StringSelector::StringPattern(_), StringSelector::ExactMatch(_)) => Ordering::Greater,
            (StringSelectorUnknown!(), StringSelector::ExactMatch(_)) => Ordering::Less,
            (StringSelectorUnknown!(), StringSelector::StringPattern(_)) => Ordering::Less,
            (StringSelectorUnknown!(), StringSelectorUnknown!()) => Ordering::Equal,
        }
    }
}

impl PartialOrd for OrdStringSelector {
    fn partial_cmp(&self, other: &OrdStringSelector) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl PartialEq for OrdStringSelector {
    fn eq(&self, other: &OrdStringSelector) -> bool {
        match (&self.0, &other.0) {
            (StringSelector::ExactMatch(s), StringSelector::ExactMatch(o)) => s.eq(o),
            (StringSelector::StringPattern(s), StringSelector::StringPattern(o)) => s.eq(o),
            (StringSelector::ExactMatch(_), StringSelector::StringPattern(_)) => false,
            (StringSelector::StringPattern(_), StringSelector::ExactMatch(_)) => false,
            (StringSelectorUnknown!(), StringSelectorUnknown!()) => true,
        }
    }
}

impl Eq for OrdStringSelector {}

#[derive(Default, Debug)]
pub struct HierarchyMatcher {
    nodes: BTreeMap<OrdStringSelector, HierarchyMatcher>,
    properties: Vec<OrdStringSelector>,
    subtree: bool,
}

impl HierarchyMatcher {
    pub fn new<I>(selectors: I) -> Result<Self, Error>
    where
        I: Iterator<Item = Selector>,
    {
        let mut matcher = HierarchyMatcher::default();
        for selector in selectors {
            selector.validate().map_err(|e| Error::Selectors(e.into()))?;

            // Safe to unwrap since we already validated the selector.
            match selector.tree_selector.unwrap() {
                TreeSelector::SubtreeSelector(subtree_selector) => {
                    matcher.insert_subtree(subtree_selector);
                }
                TreeSelector::PropertySelector(property_selector) => {
                    matcher.insert_property(property_selector);
                }
                _ => return Err(Error::Selectors(selectors::Error::InvalidTreeSelector)),
            }
        }
        Ok(matcher)
    }

    fn insert_subtree(&mut self, selector: SubtreeSelector) {
        self.insert(selector.node_path, None);
    }

    fn insert_property(&mut self, selector: PropertySelector) {
        self.insert(selector.node_path, Some(selector.target_properties));
    }

    fn insert(&mut self, node_path: Vec<StringSelector>, property: Option<StringSelector>) {
        // Note: this could have additional optimization so that branches are collapsed into a
        // single one (for example foo/bar is included by f*o/bar), however, in practice, we don't
        // hit that edge case.
        let mut matcher = self;
        for node in node_path {
            matcher = matcher.nodes.entry(node.into()).or_default();
        }
        match property {
            Some(property) => {
                matcher.properties.push(property.into());
            }
            None => matcher.subtree = true,
        }
    }
}

#[derive(Debug, PartialEq)]
pub enum SelectResult<'a, Key: Clone> {
    Properties(Vec<Cow<'a, Property<Key>>>),
    Nodes(Vec<Cow<'a, DiagnosticsHierarchy<Key>>>),
}

impl<'a, Key: Clone> SelectResult<'a, Key> {
    pub fn into_owned(self) -> SelectResult<'static, Key> {
        match self {
            Self::Properties(v) => SelectResult::Properties(
                v.into_iter().map(|v| Cow::Owned(v.into_owned())).collect(),
            ),
            Self::Nodes(v) => {
                SelectResult::Nodes(v.into_iter().map(|v| Cow::Owned(v.into_owned())).collect())
            }
        }
    }

    /// Returns Err(()) if `self` is `Self::Nodes`. Otherwise, adds to property list.
    fn add_property(&mut self, prop: &'a Property<Key>) {
        let Self::Properties(v) = self else {
            panic!("must be Self::Properties to call add_property");
        };
        v.push(Cow::Borrowed(prop));
    }

    /// Returns Err(()) if `self` is `Self::Properties`. Otherwise, adds to property list.
    fn add_node(&mut self, node: &'a DiagnosticsHierarchy<Key>) {
        let Self::Nodes(v) = self else {
            panic!("must be Self::Nodes to call add_node");
        };
        v.push(Cow::Borrowed(node));
    }
}

pub fn select_from_hierarchy<'a, 'b, Key>(
    root_node: &'a DiagnosticsHierarchy<Key>,
    selector: &'b Selector,
) -> Result<SelectResult<'a, Key>, Error>
where
    Key: AsRef<str> + Clone,
    'a: 'b,
{
    selector.validate()?;

    struct StackEntry<'a, Key> {
        node: &'a DiagnosticsHierarchy<Key>,
        node_path_index: usize,
        explored_path: Vec<&'a str>,
    }

    // Safe to unwrap since we validated above.
    let (node_path, property_selector, stack_entry) = match selector.tree_selector.as_ref().unwrap()
    {
        TreeSelector::SubtreeSelector(ref subtree_selector) => (
            &subtree_selector.node_path,
            None,
            StackEntry { node: root_node, node_path_index: 0, explored_path: vec![] },
        ),
        TreeSelector::PropertySelector(ref property_selector) => (
            &property_selector.node_path,
            Some(&property_selector.target_properties),
            StackEntry { node: root_node, node_path_index: 0, explored_path: vec![] },
        ),
        _ => return Err(Error::InvalidTreeSelector),
    };

    let mut stack = vec![stack_entry];
    let mut result = if property_selector.is_some() {
        SelectResult::Properties(vec![])
    } else {
        SelectResult::Nodes(vec![])
    };

    while let Some(StackEntry { node, node_path_index, mut explored_path }) = stack.pop() {
        // Unwrap is safe since we validate is_empty right above.
        if !selectors::match_string(&node_path[node_path_index], &node.name) {
            continue;
        }
        explored_path.push(&node.name);

        // If we are at the last node in the path, then we just need to explore the properties.
        // Otherwise, we explore the children of the current node and the properties.
        if node_path_index != node_path.len() - 1 {
            // If this node matches the next selector we are looking at, then explore its children.
            for child in node.children.iter() {
                stack.push(StackEntry {
                    node: child,
                    node_path_index: node_path_index + 1,
                    explored_path: explored_path.clone(),
                });
            }
        } else if let Some(s) = property_selector {
            // If we have a property selector, then add any properties matching it to our result.
            for property in &node.properties {
                if selectors::match_string(s, property.key()) {
                    result.add_property(property);
                }
            }
        } else {
            // If we don't have a property selector and we reached the end of the node path, then
            // we should add the current node to the result.
            result.add_node(node);
        }
    }

    Ok(result)
}

/// Filters a hierarchy given a tree selector.
pub fn filter_tree<'a, Key, I: IntoIterator<Item = &'a TreeSelector>>(
    root_node: DiagnosticsHierarchy<Key>,
    selectors: I,
) -> Option<DiagnosticsHierarchy<Key>>
where
    Key: AsRef<str>,
{
    let mut matcher = HierarchyMatcher::default();
    for selector in selectors.into_iter() {
        match selector {
            TreeSelector::SubtreeSelector(subtree_selector) => {
                matcher.insert_subtree(subtree_selector.clone());
            }
            TreeSelector::PropertySelector(property_selector) => {
                matcher.insert_property(property_selector.clone());
            }
            _ => {}
        }
    }
    filter_hierarchy(root_node, &matcher)
}

/// Filters a diagnostics hierarchy using a set of path selectors and their associated property
/// selectors.
///
/// If the return type is None that implies that the filter encountered no errors AND the tree was
/// filtered to be empty at the end.
pub fn filter_hierarchy<Key>(
    mut root_node: DiagnosticsHierarchy<Key>,
    hierarchy_matcher: &HierarchyMatcher,
) -> Option<DiagnosticsHierarchy<Key>>
where
    Key: AsRef<str>,
{
    let starts_empty = root_node.children.is_empty() && root_node.properties.is_empty();
    if filter_hierarchy_helper(&mut root_node, &[hierarchy_matcher]) {
        if !starts_empty && root_node.children.is_empty() && root_node.properties.is_empty() {
            return None;
        }
        return Some(root_node);
    }
    None
}

fn filter_hierarchy_helper<Key>(
    node: &mut DiagnosticsHierarchy<Key>,
    hierarchy_matchers: &[&HierarchyMatcher],
) -> bool
where
    Key: AsRef<str>,
{
    let child_matchers = eval_matchers_on_node_name(&node.name, hierarchy_matchers);
    if child_matchers.is_empty() {
        node.children.clear();
        node.properties.clear();
        return false;
    }

    if child_matchers.iter().any(|m| m.subtree) {
        return true;
    }

    node.children.retain_mut(|child| filter_hierarchy_helper(child, &child_matchers));
    node.properties.retain_mut(|prop| eval_matchers_on_property(prop.name(), &child_matchers));

    !(node.children.is_empty() && node.properties.is_empty())
}

fn eval_matchers_on_node_name<'a>(
    node_name: &'a str,
    matchers: &'a [&'a HierarchyMatcher],
) -> Vec<&'a HierarchyMatcher> {
    let mut result = vec![];
    for matcher in matchers {
        for (node_pattern, tree_matcher) in matcher.nodes.iter() {
            if selectors::match_string(&node_pattern.0, node_name) {
                result.push(tree_matcher);
            }
        }
    }
    result
}

fn eval_matchers_on_property(property_name: &str, matchers: &[&HierarchyMatcher]) -> bool {
    matchers.iter().any(|matcher| {
        matcher
            .properties
            .iter()
            .any(|property_pattern| selectors::match_string(&property_pattern.0, property_name))
    })
}

/// The parameters of an exponential histogram.
#[derive(Clone)]
pub struct ExponentialHistogramParams<T: Clone> {
    /// The floor of the exponential histogram.
    pub floor: T,

    /// The initial step of the exponential histogram.
    pub initial_step: T,

    /// The step multiplier of the exponential histogram.
    pub step_multiplier: T,

    /// The number of buckets that the exponential histogram can have. This doesn't include the
    /// overflow and underflow buckets.
    pub buckets: usize,
}

/// The parameters of a linear histogram.
#[derive(Clone)]
pub struct LinearHistogramParams<T: Clone> {
    /// The floor of the linear histogram.
    pub floor: T,

    /// The step size of the linear histogram.
    pub step_size: T,

    /// The number of buckets that the linear histogram can have. This doesn't include the overflow
    /// and underflow buckets.
    pub buckets: usize,
}

/// A type which can function as a "view" into a diagnostics hierarchy, optionally allocating a new
/// instance to service a request.
pub trait DiagnosticsHierarchyGetter<K: Clone> {
    fn get_diagnostics_hierarchy<'a>(
        &'a self,
    ) -> impl std::future::Future<Output = Cow<'_, DiagnosticsHierarchy<K>>>
    where
        K: 'a;
}

impl<K: Clone> DiagnosticsHierarchyGetter<K> for DiagnosticsHierarchy<K> {
    async fn get_diagnostics_hierarchy<'a>(&'a self) -> Cow<'_, DiagnosticsHierarchy<K>>
    where
        K: 'a,
    {
        Cow::Borrowed(self)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::testing::CondensableOnDemand;
    use test_case::test_case;

    use assert_matches::assert_matches;
    use selectors::VerboseError;
    use std::sync::Arc;

    fn validate_hierarchy_iteration(
        mut results_vec: Vec<(Vec<String>, Option<Property>)>,
        test_hierarchy: DiagnosticsHierarchy,
    ) {
        let expected_num_entries = results_vec.len();
        let mut num_entries = 0;
        for (key, val) in test_hierarchy.property_iter() {
            num_entries += 1;
            let (expected_key, expected_property) = results_vec.pop().unwrap();
            assert_eq!(key.to_vec().join("/"), expected_key.to_vec().join("/"));
            assert_eq!(val, expected_property.as_ref());
        }

        assert_eq!(num_entries, expected_num_entries);
    }

    #[track_caller]
    fn validate_hierarchy_error_iteration(
        mut results_vec: Vec<(Vec<String>, Option<MissingValue>)>,
        test_hierarchy: DiagnosticsHierarchy,
    ) {
        let expected_num_entries = results_vec.len();
        let mut num_entries = 0;
        for (key, reason) in test_hierarchy.error_iter() {
            num_entries += 1;
            let (expected_key, expected_reason) = results_vec.pop().unwrap();
            assert_eq!(reason, expected_reason.as_ref());
            assert_eq!(key.to_vec().join("/"), expected_key.to_vec().join("/"));
        }

        assert_eq!(num_entries, expected_num_entries);
    }

    #[fuchsia::test]
    fn test_diagnostics_hierarchy_property_iteration() {
        let double_array_data = vec![-1.2, 2.3, 3.4, 4.5, -5.6];
        let chars = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
        let string_data = chars.iter().cycle().take(6000).collect::<String>();
        let bytes_data = (0u8..=9u8).cycle().take(5000).collect::<Vec<u8>>();

        let test_hierarchy = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![
                Property::Int("int-root".to_string(), 3),
                Property::DoubleArray(
                    "property-double-array".to_string(),
                    ArrayContent::Values(double_array_data.clone()),
                ),
            ],
            vec![DiagnosticsHierarchy::new(
                "child-1".to_string(),
                vec![
                    Property::Uint("property-uint".to_string(), 10),
                    Property::Double("property-double".to_string(), -3.4),
                    Property::String("property-string".to_string(), string_data.clone()),
                    Property::IntArray(
                        "property-int-array".to_string(),
                        ArrayContent::new(vec![1, 2, 1, 1, 1, 1, 1], ArrayFormat::LinearHistogram)
                            .unwrap(),
                    ),
                ],
                vec![DiagnosticsHierarchy::new(
                    "child-1-1".to_string(),
                    vec![
                        Property::Int("property-int".to_string(), -9),
                        Property::Bytes("property-bytes".to_string(), bytes_data.clone()),
                        Property::UintArray(
                            "property-uint-array".to_string(),
                            ArrayContent::new(
                                vec![1, 1, 2, 0, 1, 1, 2, 0, 0],
                                ArrayFormat::ExponentialHistogram,
                            )
                            .unwrap(),
                        ),
                    ],
                    vec![],
                )],
            )],
        );

        let results_vec = vec![
            (
                vec!["root".to_string(), "child-1".to_string(), "child-1-1".to_string()],
                Some(Property::UintArray(
                    "property-uint-array".to_string(),
                    ArrayContent::new(
                        vec![1, 1, 2, 0, 1, 1, 2, 0, 0],
                        ArrayFormat::ExponentialHistogram,
                    )
                    .unwrap(),
                )),
            ),
            (
                vec!["root".to_string(), "child-1".to_string(), "child-1-1".to_string()],
                Some(Property::Bytes("property-bytes".to_string(), bytes_data)),
            ),
            (
                vec!["root".to_string(), "child-1".to_string(), "child-1-1".to_string()],
                Some(Property::Int("property-int".to_string(), -9)),
            ),
            (
                vec!["root".to_string(), "child-1".to_string()],
                Some(Property::IntArray(
                    "property-int-array".to_string(),
                    ArrayContent::new(vec![1, 2, 1, 1, 1, 1, 1], ArrayFormat::LinearHistogram)
                        .unwrap(),
                )),
            ),
            (
                vec!["root".to_string(), "child-1".to_string()],
                Some(Property::String("property-string".to_string(), string_data)),
            ),
            (
                vec!["root".to_string(), "child-1".to_string()],
                Some(Property::Double("property-double".to_string(), -3.4)),
            ),
            (
                vec!["root".to_string(), "child-1".to_string()],
                Some(Property::Uint("property-uint".to_string(), 10)),
            ),
            (
                vec!["root".to_string()],
                Some(Property::DoubleArray(
                    "property-double-array".to_string(),
                    ArrayContent::Values(double_array_data),
                )),
            ),
            (vec!["root".to_string()], Some(Property::Int("int-root".to_string(), 3))),
        ];

        validate_hierarchy_iteration(results_vec, test_hierarchy);
    }

    #[fuchsia::test]
    fn test_diagnostics_hierarchy_error_iteration() {
        let mut test_hierarchy = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![],
            vec![
                DiagnosticsHierarchy::new(
                    "child-1".to_string(),
                    vec![],
                    vec![DiagnosticsHierarchy::new("child-1-1".to_string(), vec![], vec![])],
                ),
                DiagnosticsHierarchy::new("child-2".to_string(), vec![], vec![]),
            ],
        );

        test_hierarchy.children[0]
            .add_missing(MissingValueReason::LinkNeverExpanded, "child-1".to_string());
        test_hierarchy.children[0].children[0]
            .add_missing(MissingValueReason::Timeout, "child-1-1".to_string());

        let results_vec = vec![
            (
                vec!["root".to_string(), "child-1".to_string(), "child-1-1".to_string()],
                Some(MissingValue {
                    reason: MissingValueReason::Timeout,
                    name: "child-1-1".to_string(),
                }),
            ),
            (
                vec!["root".to_string(), "child-1".to_string()],
                Some(MissingValue {
                    reason: MissingValueReason::LinkNeverExpanded,
                    name: "child-1".to_string(),
                }),
            ),
            (vec!["root".to_string(), "child-2".to_string()], None),
            (vec!["root".to_string()], None),
        ];

        validate_hierarchy_error_iteration(results_vec, test_hierarchy);
    }

    #[fuchsia::test]
    fn test_getters() {
        let a_prop = Property::Int("a".to_string(), 1);
        let b_prop = Property::Uint("b".to_string(), 2);
        let child2 = DiagnosticsHierarchy::new("child2".to_string(), vec![], vec![]);
        let child = DiagnosticsHierarchy::new(
            "child".to_string(),
            vec![b_prop.clone()],
            vec![child2.clone()],
        );
        let mut hierarchy = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![a_prop.clone()],
            vec![child.clone()],
        );
        assert_matches!(hierarchy.get_child("child"), Some(node) if *node == child);
        assert_matches!(hierarchy.get_child_mut("child"), Some(node) if *node == child);
        assert_matches!(hierarchy.get_child_by_path(&["child", "child2"]),
                        Some(node) if *node == child2);
        assert_matches!(hierarchy.get_child_by_path_mut(&["child", "child2"]),
                        Some(node) if *node == child2);
        assert_matches!(hierarchy.get_property("a"), Some(prop) if *prop == a_prop);
        assert_matches!(hierarchy.get_property_by_path(&["child", "b"]),
                        Some(prop) if *prop == b_prop);
    }

    #[fuchsia::test]
    fn test_edge_case_hierarchy_iteration() {
        let root_only_with_one_property_hierarchy = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::Int("property-int".to_string(), -9)],
            vec![],
        );

        let results_vec =
            vec![(vec!["root".to_string()], Some(Property::Int("property-int".to_string(), -9)))];

        validate_hierarchy_iteration(results_vec, root_only_with_one_property_hierarchy);

        let empty_hierarchy = DiagnosticsHierarchy::new("root".to_string(), vec![], vec![]);

        let results_vec = vec![(vec!["root".to_string()], None)];

        validate_hierarchy_iteration(results_vec, empty_hierarchy);

        let empty_root_populated_child = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "foo",
                vec![Property::Int("11".to_string(), -4)],
                vec![],
            )],
        );

        let results_vec = vec![
            (
                vec!["root".to_string(), "foo".to_string()],
                Some(Property::Int("11".to_string(), -4)),
            ),
            (vec!["root".to_string()], None),
        ];

        validate_hierarchy_iteration(results_vec, empty_root_populated_child);

        let empty_root_empty_child = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new("foo", vec![], vec![])],
        );

        let results_vec = vec![
            (vec!["root".to_string(), "foo".to_string()], None),
            (vec!["root".to_string()], None),
        ];

        validate_hierarchy_iteration(results_vec, empty_root_empty_child);
    }

    #[fuchsia::test]
    fn array_value() {
        let values = vec![1, 2, 5, 7, 9, 11, 13];
        let array = ArrayContent::<u64>::new(values.clone(), ArrayFormat::Default);
        assert_matches!(array, Ok(ArrayContent::Values(vals)) if vals == values);
    }

    #[fuchsia::test]
    fn linear_histogram_array_value() {
        let values = vec![1, 2, 5, 7, 9, 11, 13];
        let array = ArrayContent::<i64>::new(values, ArrayFormat::LinearHistogram);
        assert_matches!(array, Ok(ArrayContent::LinearHistogram(hist))
            if hist == LinearHistogram {
                floor: 1,
                step: 2,
                counts: vec![5, 7, 9, 11, 13],
                indexes: None,
                size: 5,
            }
        );
    }

    #[fuchsia::test]
    fn exponential_histogram_array_value() {
        let values = vec![1.0, 2.0, 5.0, 7.0, 9.0, 11.0, 15.0];
        let array = ArrayContent::<f64>::new(values, ArrayFormat::ExponentialHistogram);
        assert_matches!(array, Ok(ArrayContent::ExponentialHistogram(hist))
            if hist == ExponentialHistogram {
                floor: 1.0,
                initial_step: 2.0,
                step_multiplier: 5.0,
                counts: vec![7.0, 9.0, 11.0, 15.0],
                indexes: None,
                size: 4,
            }
        );
    }

    #[fuchsia::test]
    fn deserialize_linear_int_histogram() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": -2,
                    "step": 3,
                    "counts": [4, 5, 6],
                    "size": 3
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        let expected = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::IntArray(
                "histogram".to_string(),
                ArrayContent::new(vec![-2, 3, 4, 5, 6], ArrayFormat::LinearHistogram).unwrap(),
            )],
            vec![],
        );
        assert_eq!(parsed, expected);
        Ok(())
    }

    #[fuchsia::test]
    fn deserialize_exponential_int_histogram() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": 1,
                    "initial_step": 3,
                    "step_multiplier": 2,
                    "counts": [4, 5, 6],
                    "size": 3
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        let expected = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::IntArray(
                "histogram".to_string(),
                ArrayContent::new(vec![1, 3, 2, 4, 5, 6], ArrayFormat::ExponentialHistogram)
                    .unwrap(),
            )],
            vec![],
        );
        assert_eq!(parsed, expected);
        Ok(())
    }

    #[fuchsia::test]
    fn deserialize_linear_uint_histogram() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": 2,
                    "step": 3,
                    "counts": [4, 9223372036854775808, 6],
                    "size": 3
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        let expected = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::UintArray(
                "histogram".to_string(),
                ArrayContent::new(
                    vec![2, 3, 4, 9_223_372_036_854_775_808, 6],
                    ArrayFormat::LinearHistogram,
                )
                .unwrap(),
            )],
            vec![],
        );
        assert_eq!(parsed, expected);
        Ok(())
    }

    #[fuchsia::test]
    fn deserialize_linear_double_histogram() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": 2.0,
                    "step": 3.0,
                    "counts": [4.0, 5.0, 6.0],
                    "size": 3
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        let expected = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::DoubleArray(
                "histogram".to_string(),
                ArrayContent::new(vec![2.0, 3.0, 4.0, 5.0, 6.0], ArrayFormat::LinearHistogram)
                    .unwrap(),
            )],
            vec![],
        );
        assert_eq!(parsed, expected);
        Ok(())
    }

    #[fuchsia::test]
    fn deserialize_sparse_histogram() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": 2,
                    "step": 3,
                    "counts": [4, 5, 6],
                    "indexes": [1, 2, 4],
                    "size": 8
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;

        let mut histogram =
            ArrayContent::new(vec![2, 3, 0, 4, 5, 0, 6, 0, 0, 0], ArrayFormat::LinearHistogram)
                .unwrap();
        histogram.condense_histogram();
        let expected = DiagnosticsHierarchy::new(
            "root".to_string(),
            vec![Property::IntArray("histogram".to_string(), histogram)],
            vec![],
        );
        assert_eq!(parsed, expected);
        Ok(())
    }

    // If a struct can't be parsed as a valid histogram, it will be created as a Node. So if
    // there's a node "histogram" (as opposed to a property "histogram") then it didn't parse
    // as a histogram.

    #[fuchsia::test]
    fn reject_histogram_incompatible_values() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": -2,
                    "step": 3,
                    "counts": [4, 9223372036854775808, 6],
                    "size": 3
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        assert_eq!(parsed.children.len(), 1);
        assert_eq!(&parsed.children[0].name, "histogram");
        Ok(())
    }

    #[fuchsia::test]
    fn reject_histogram_bad_sparse_list() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": -2,
                    "step": 3,
                    "counts": [4, 5, 6],
                    "indexes": [0, 1, 2, 3],
                    "size": 8
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        assert_eq!(parsed.children.len(), 1);
        assert_eq!(&parsed.children[0].name, "histogram");
        Ok(())
    }

    #[fuchsia::test]
    fn reject_histogram_bad_index() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": -2,
                    "step": 3,
                    "counts": [4, 5, 6],
                    "indexes": [0, 1, 4],
                    "size": 4
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        assert_eq!(parsed.children.len(), 1);
        assert_eq!(&parsed.children[0].name, "histogram");
        Ok(())
    }

    #[fuchsia::test]
    fn reject_histogram_wrong_field() -> Result<(), serde_json::Error> {
        let json = r#"{
            "root": {
                "histogram": {
                    "floor": 2,
                    "step": 3,
                    "counts": [4, 5, 6],
                    "incorrect": [0, 1, 3],
                    "size": 4
                }
            }
        }"#;
        let parsed: DiagnosticsHierarchy = serde_json::from_str(json)?;
        assert_eq!(parsed.children.len(), 1);
        assert_eq!(&parsed.children[0].name, "histogram");
        Ok(())
    }

    #[fuchsia::test]
    fn exponential_histogram() {
        let values = vec![0, 2, 4, 0, 1, 2, 3, 4, 5];
        let array = ArrayContent::new(values, ArrayFormat::ExponentialHistogram);
        assert_matches!(array, Ok(ArrayContent::ExponentialHistogram(hist))
            if hist == ExponentialHistogram {
                floor: 0,
                initial_step: 2,
                step_multiplier: 4,
                counts: vec![0, 1, 2, 3, 4, 5],
                indexes: None,
                size: 6,
            }
        );
    }

    #[fuchsia::test]
    fn add_to_hierarchy() {
        let mut hierarchy = DiagnosticsHierarchy::new_root();
        let prop_1 = Property::String("x".to_string(), "foo".to_string());
        let path_1 = vec!["root", "one"];
        let prop_2 = Property::Uint("c".to_string(), 3);
        let path_2 = vec!["root", "two"];
        let prop_2_prime = Property::Int("z".to_string(), -4);
        hierarchy.add_property_at_path(&path_1, prop_1.clone());
        hierarchy.add_property_at_path(&path_2.clone(), prop_2.clone());
        hierarchy.add_property_at_path(&path_2, prop_2_prime.clone());

        assert_eq!(
            hierarchy,
            DiagnosticsHierarchy {
                name: "root".to_string(),
                children: vec![
                    DiagnosticsHierarchy {
                        name: "one".to_string(),
                        properties: vec![prop_1],
                        children: vec![],
                        missing: vec![],
                    },
                    DiagnosticsHierarchy {
                        name: "two".to_string(),
                        properties: vec![prop_2, prop_2_prime],
                        children: vec![],
                        missing: vec![],
                    }
                ],
                properties: vec![],
                missing: vec![],
            }
        );
    }

    #[fuchsia::test]
    fn string_lists() {
        let mut hierarchy = DiagnosticsHierarchy::new_root();
        let prop_1 =
            Property::StringList("x".to_string(), vec!["foo".to_string(), "bar".to_string()]);
        let path_1 = vec!["root", "one"];
        hierarchy.add_property_at_path(&path_1, prop_1.clone());

        assert_eq!(
            hierarchy,
            DiagnosticsHierarchy {
                name: "root".to_string(),
                children: vec![DiagnosticsHierarchy {
                    name: "one".to_string(),
                    properties: vec![prop_1],
                    children: vec![],
                    missing: vec![],
                },],
                properties: vec![],
                missing: vec![],
            }
        );
    }

    #[fuchsia::test]
    // TODO(https://fxbug.dev/42169733): delete the below
    #[cfg_attr(feature = "variant_asan", ignore)]
    #[cfg_attr(feature = "variant_hwasan", ignore)]
    #[should_panic]
    // Empty paths are meaningless on insertion and break the method invariant.
    fn no_empty_paths_allowed() {
        let mut hierarchy = DiagnosticsHierarchy::<String>::new_root();
        let path_1: Vec<&String> = vec![];
        hierarchy.get_or_add_node(&path_1);
    }

    #[fuchsia::test]
    #[should_panic]
    // Paths provided to add must begin at the node we're calling
    // add() on.
    fn path_must_start_at_self() {
        let mut hierarchy = DiagnosticsHierarchy::<String>::new_root();
        let path_1 = vec!["not_root", "a"];
        hierarchy.get_or_add_node(&path_1);
    }

    #[fuchsia::test]
    fn sort_hierarchy() {
        let mut hierarchy = DiagnosticsHierarchy::new(
            "root",
            vec![
                Property::String("x".to_string(), "foo".to_string()),
                Property::Uint("c".to_string(), 3),
                Property::Int("z".to_string(), -4),
            ],
            vec![
                DiagnosticsHierarchy::new(
                    "foo",
                    vec![
                        Property::Int("11".to_string(), -4),
                        Property::Bytes("123".to_string(), "foo".bytes().collect()),
                        Property::Double("0".to_string(), 8.1),
                    ],
                    vec![],
                ),
                DiagnosticsHierarchy::new("bar", vec![], vec![]),
            ],
        );

        hierarchy.sort();

        let sorted_hierarchy = DiagnosticsHierarchy::new(
            "root",
            vec![
                Property::Uint("c".to_string(), 3),
                Property::String("x".to_string(), "foo".to_string()),
                Property::Int("z".to_string(), -4),
            ],
            vec![
                DiagnosticsHierarchy::new("bar", vec![], vec![]),
                DiagnosticsHierarchy::new(
                    "foo",
                    vec![
                        Property::Double("0".to_string(), 8.1),
                        Property::Int("11".to_string(), -4),
                        Property::Bytes("123".to_string(), "foo".bytes().collect()),
                    ],
                    vec![],
                ),
            ],
        );
        assert_eq!(sorted_hierarchy, hierarchy);
    }

    fn parse_selectors_and_filter_hierarchy(
        hierarchy: DiagnosticsHierarchy,
        test_selectors: Vec<&str>,
    ) -> Option<DiagnosticsHierarchy> {
        let parsed_test_selectors = test_selectors
            .into_iter()
            .map(|selector_string| {
                Arc::new(
                    selectors::parse_selector::<VerboseError>(selector_string)
                        .expect("All test selectors are valid and parsable."),
                )
            })
            .collect::<Vec<Arc<Selector>>>();

        let hierarchy_matcher: HierarchyMatcher = parsed_test_selectors.try_into().unwrap();

        filter_hierarchy(hierarchy, &hierarchy_matcher).map(|mut hierarchy| {
            hierarchy.sort();
            hierarchy
        })
    }

    fn get_test_hierarchy() -> DiagnosticsHierarchy {
        DiagnosticsHierarchy::new(
            "root",
            vec![
                Property::String("x".to_string(), "foo".to_string()),
                Property::Uint("c".to_string(), 3),
                Property::Int("z".to_string(), -4),
            ],
            vec![
                make_foo(),
                DiagnosticsHierarchy::new(
                    "bar",
                    vec![Property::Int("12".to_string(), -4)],
                    vec![DiagnosticsHierarchy::new(
                        "zed",
                        vec![Property::Int("13/:".to_string(), -4)],
                        vec![],
                    )],
                ),
            ],
        )
    }

    fn make_all_foo_props() -> Vec<Property> {
        vec![
            Property::Int("11".to_string(), -4),
            Property::Bytes("123".to_string(), b"foo".to_vec()),
            Property::Double("0".to_string(), 8.1),
        ]
    }

    fn make_zed() -> Vec<DiagnosticsHierarchy> {
        vec![DiagnosticsHierarchy::new("zed", vec![Property::Int("13".to_string(), -4)], vec![])]
    }

    fn make_foo() -> DiagnosticsHierarchy {
        DiagnosticsHierarchy::new("foo", make_all_foo_props(), make_zed())
    }

    #[fuchsia::test]
    fn test_filter_hierarchy() {
        let test_selectors = vec!["*:root/foo:11", "*:root:z", r#"*:root/bar/zed:13\/\:"#];

        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            Some(DiagnosticsHierarchy::new(
                "root",
                vec![Property::Int("z".to_string(), -4),],
                vec![
                    DiagnosticsHierarchy::new(
                        "bar",
                        vec![],
                        vec![DiagnosticsHierarchy::new(
                            "zed",
                            vec![Property::Int("13/:".to_string(), -4)],
                            vec![],
                        )],
                    ),
                    DiagnosticsHierarchy::new(
                        "foo",
                        vec![Property::Int("11".to_string(), -4),],
                        vec![],
                    )
                ],
            ))
        );

        let test_selectors = vec!["*:root"];
        let mut sorted_expected = get_test_hierarchy();
        sorted_expected.sort();
        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            Some(sorted_expected)
        );
    }

    #[fuchsia::test]
    fn test_filter_does_not_include_empty_node() {
        let test_selectors = vec!["*:root/foo:blorg"];

        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            None,
        );
    }

    #[fuchsia::test]
    fn test_filter_empty_hierarchy() {
        let test_selectors = vec!["*:root"];

        assert_eq!(
            parse_selectors_and_filter_hierarchy(
                DiagnosticsHierarchy::new("root", vec![], vec![]),
                test_selectors
            ),
            Some(DiagnosticsHierarchy::new("root", vec![], vec![])),
        );
    }

    #[fuchsia::test]
    fn test_full_filtering() {
        // If we select a non-existent root, then we return a fully filtered hierarchy.
        let test_selectors = vec!["*:non-existent-root"];
        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            None,
        );

        // If we select a non-existent child of the root, then we return a fully filtered hierarchy.
        let test_selectors = vec!["*:root/i-dont-exist:foo"];
        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            None,
        );

        // Even if the root exists, but we don't include any property, we consider the hierarchy
        // fully filtered. This is aligned with the previous case.
        let test_selectors = vec!["*:root:i-dont-exist"];
        assert_eq!(
            parse_selectors_and_filter_hierarchy(get_test_hierarchy(), test_selectors),
            None,
        );
    }

    #[fuchsia::test]
    fn test_subtree_selection_includes_empty_nodes() {
        let test_selectors = vec!["*:root"];
        let mut empty_hierarchy = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![
                DiagnosticsHierarchy::new(
                    "foo",
                    vec![],
                    vec![DiagnosticsHierarchy::new("zed", vec![], vec![])],
                ),
                DiagnosticsHierarchy::new(
                    "bar",
                    vec![],
                    vec![DiagnosticsHierarchy::new("zed", vec![], vec![])],
                ),
            ],
        );

        empty_hierarchy.sort();

        assert_eq!(
            parse_selectors_and_filter_hierarchy(empty_hierarchy.clone(), test_selectors),
            Some(empty_hierarchy)
        );
    }

    #[fuchsia::test]
    fn test_empty_tree_filtering() {
        // Subtree selection on the empty tree should produce the empty tree.
        let mut empty_hierarchy = DiagnosticsHierarchy::new("root", vec![], vec![]);
        empty_hierarchy.sort();

        let subtree_selector = vec!["*:root"];
        assert_eq!(
            parse_selectors_and_filter_hierarchy(empty_hierarchy.clone(), subtree_selector),
            Some(empty_hierarchy.clone())
        );

        // Selecting a property on the root, even if it doesn't exist, should produce nothing.
        let fake_property_selector = vec!["*:root:blorp"];
        assert_eq!(
            parse_selectors_and_filter_hierarchy(empty_hierarchy.clone(), fake_property_selector),
            None,
        );
    }

    #[test_case(vec![Property::Int("11".to_string(), -4)], "root/foo:11" ; "specific_property")]
    #[test_case(make_all_foo_props(), "root/foo:*" ; "many_properties")]
    #[test_case(vec![], "root/foo:none" ; "property_not_there")]
    #[fuchsia::test]
    fn test_select_from_hierarchy_property_selectors(expected: Vec<Property>, tree_selector: &str) {
        let hierarchy = get_test_hierarchy();
        let parsed_selector =
            selectors::parse_selector::<VerboseError>(&format!("*:{tree_selector}"))
                .expect("All test selectors are valid and parsable.");
        let Ok(SelectResult::Properties(mut property_entry_vec)) =
            select_from_hierarchy(&hierarchy, &parsed_selector)
        else {
            panic!("must be properties");
        };

        property_entry_vec.sort_by(|p1, p2| p1.name().cmp(p2.name()));
        let mut expected = expected.iter().map(Cow::Borrowed).collect::<Vec<_>>();
        expected.sort_by(|p1, p2| p1.name().cmp(p2.name()));

        assert_eq!(property_entry_vec, expected);
    }

    #[test_case(vec![], "root/none" ; "node_not_there")]
    #[test_case(make_zed(), "root/foo/zed" ; "properties_only")]
    #[test_case(vec![make_foo()], "root/foo" ; "nodes_and_properties")]
    #[test_case(vec![get_test_hierarchy()], "root" ; "select_root")]
    #[fuchsia::test]
    fn test_select_from_hierarchy_tree_selectors(
        expected: Vec<DiagnosticsHierarchy>,
        tree_selector: &str,
    ) {
        let hierarchy = get_test_hierarchy();
        let parsed_selector =
            selectors::parse_selector::<VerboseError>(&format!("*:{tree_selector}"))
                .expect("All test selectors are valid and parsable.");
        let Ok(SelectResult::Nodes(node_vec)) = select_from_hierarchy(&hierarchy, &parsed_selector)
        else {
            panic!("must be nodes");
        };

        let expected = expected.iter().map(Cow::Borrowed).collect::<Vec<_>>();

        assert_eq!(node_vec, expected);
    }

    #[fuchsia::test]
    fn sort_numerical_value() {
        let mut diagnostics_hierarchy = DiagnosticsHierarchy::new(
            "root",
            vec![
                Property::Double("2".to_string(), 2.3),
                Property::Int("0".to_string(), -4),
                Property::Uint("10".to_string(), 3),
                Property::String("1".to_string(), "test".to_string()),
            ],
            vec![
                DiagnosticsHierarchy::new("123", vec![], vec![]),
                DiagnosticsHierarchy::new("34", vec![], vec![]),
                DiagnosticsHierarchy::new("4", vec![], vec![]),
                DiagnosticsHierarchy::new("023", vec![], vec![]),
                DiagnosticsHierarchy::new("12", vec![], vec![]),
                DiagnosticsHierarchy::new("1", vec![], vec![]),
            ],
        );
        diagnostics_hierarchy.sort();
        assert_eq!(
            diagnostics_hierarchy,
            DiagnosticsHierarchy::new(
                "root",
                vec![
                    Property::Int("0".to_string(), -4),
                    Property::String("1".to_string(), "test".to_string()),
                    Property::Double("2".to_string(), 2.3),
                    Property::Uint("10".to_string(), 3),
                ],
                vec![
                    DiagnosticsHierarchy::new("1", vec![], vec![]),
                    DiagnosticsHierarchy::new("4", vec![], vec![]),
                    DiagnosticsHierarchy::new("12", vec![], vec![]),
                    DiagnosticsHierarchy::new("023", vec![], vec![]),
                    DiagnosticsHierarchy::new("34", vec![], vec![]),
                    DiagnosticsHierarchy::new("123", vec![], vec![]),
                ]
            )
        );
    }

    #[fuchsia::test]
    fn filter_hierarchy_doesnt_return_partial_matches() {
        let hierarchy = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new("session_started_at", vec![], vec![])],
        );
        let test_selectors = vec!["*:root/session_started_at/0"];
        assert_eq!(parse_selectors_and_filter_hierarchy(hierarchy, test_selectors), None);
    }

    #[fuchsia::test]
    fn test_filter_tree() {
        let test_selectors = vec!["root/foo:11", "root:z", r#"root/bar/zed:13\/\:"#];
        let parsed_test_selectors = test_selectors
            .into_iter()
            .map(|s| {
                selectors::parse_tree_selector::<VerboseError>(s)
                    .expect("All test selectors are valid and parsable.")
            })
            .collect::<Vec<_>>();

        let result =
            filter_tree(get_test_hierarchy(), &parsed_test_selectors).map(|mut hierarchy| {
                hierarchy.sort();
                hierarchy
            });
        assert_eq!(
            result,
            Some(DiagnosticsHierarchy::new(
                "root",
                vec![Property::Int("z".to_string(), -4),],
                vec![
                    DiagnosticsHierarchy::new(
                        "bar",
                        vec![],
                        vec![DiagnosticsHierarchy::new(
                            "zed",
                            vec![Property::Int("13/:".to_string(), -4)],
                            vec![],
                        )],
                    ),
                    DiagnosticsHierarchy::new(
                        "foo",
                        vec![Property::Int("11".to_string(), -4),],
                        vec![],
                    )
                ],
            ))
        );
    }

    #[fuchsia::test]
    fn test_matcher_from_iterator() {
        let matcher = HierarchyMatcher::new(
            ["*:root/foo:11", "*:root:z", r#"*:root/bar/zed:13\/\:"#].into_iter().map(|s| {
                selectors::parse_selector::<VerboseError>(s)
                    .expect("All test selectors are valid and parsable.")
            }),
        )
        .expect("create matcher from iterator of selectors");
        let result = filter_hierarchy(get_test_hierarchy(), &matcher).map(|mut hierarchy| {
            hierarchy.sort();
            hierarchy
        });
        assert_eq!(
            result,
            Some(DiagnosticsHierarchy::new(
                "root",
                vec![Property::Int("z".to_string(), -4),],
                vec![
                    DiagnosticsHierarchy::new(
                        "bar",
                        vec![],
                        vec![DiagnosticsHierarchy::new(
                            "zed",
                            vec![Property::Int("13/:".to_string(), -4)],
                            vec![],
                        )],
                    ),
                    DiagnosticsHierarchy::new(
                        "foo",
                        vec![Property::Int("11".to_string(), -4),],
                        vec![],
                    )
                ],
            ))
        );
    }

    #[test_case(DiagnosticsHierarchy::new_root() ; "empty")]
    #[test_case(DiagnosticsHierarchy::new(
        "root",
        vec![Property::String("x".to_string(), "foo".to_string())],
        vec![],
    ) ; "properties")]
    #[test_case(DiagnosticsHierarchy::new(
        "root",
        vec![],
        vec![DiagnosticsHierarchy::new_root()],
    ) ; "children")]
    #[fuchsia::test]
    fn test_merge_hierarchy_empty(other: DiagnosticsHierarchy) {
        let mut hierarchy = DiagnosticsHierarchy::new_root();
        hierarchy.merge(other.clone());
        assert_eq!(hierarchy, other);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_properties_and_children() {
        let mut a = DiagnosticsHierarchy::new(
            "root",
            vec![Property::Int("a".to_string(), 1)],
            vec![DiagnosticsHierarchy::new("child_a", vec![], vec![])],
        );
        let b = DiagnosticsHierarchy::new(
            "root",
            vec![Property::String("b".to_string(), "foo".to_string())],
            vec![DiagnosticsHierarchy::new("child_b", vec![], vec![])],
        );
        a.merge(b);
        let expected = DiagnosticsHierarchy::new(
            "root",
            vec![
                Property::Int("a".to_string(), 1),
                Property::String("b".to_string(), "foo".to_string()),
            ],
            vec![
                DiagnosticsHierarchy::new("child_a", vec![], vec![]),
                DiagnosticsHierarchy::new("child_b", vec![], vec![]),
            ],
        );
        assert_eq!(a, expected);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_nested_children() {
        let mut a = DiagnosticsHierarchy::<String>::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![],
                vec![DiagnosticsHierarchy::new("grandchild_a", vec![], vec![])],
            )],
        );
        let b = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![],
                vec![DiagnosticsHierarchy::new("grandchild_b", vec![], vec![])],
            )],
        );
        a.merge(b);
        let expected = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![],
                vec![
                    DiagnosticsHierarchy::new("grandchild_a", vec![], vec![]),
                    DiagnosticsHierarchy::new("grandchild_b", vec![], vec![]),
                ],
            )],
        );
        assert_eq!(a, expected);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_missing() {
        let mut a: DiagnosticsHierarchy<String> = DiagnosticsHierarchy::new_root();
        a.add_missing(MissingValueReason::LinkNotFound, "a".to_string());
        let mut b = DiagnosticsHierarchy::new_root();
        b.add_missing(MissingValueReason::LinkParseFailure, "b".to_string());
        a.merge(b);
        let expected = DiagnosticsHierarchy {
            missing: vec![
                MissingValue { reason: MissingValueReason::LinkNotFound, name: "a".to_string() },
                MissingValue {
                    reason: MissingValueReason::LinkParseFailure,
                    name: "b".to_string(),
                },
            ],
            ..DiagnosticsHierarchy::new_root()
        };
        assert_eq!(a, expected);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_missing_no_duplicates() {
        let mut a: DiagnosticsHierarchy<String> = DiagnosticsHierarchy::new_root();
        a.add_missing(MissingValueReason::LinkNotFound, "a".to_string());
        let mut b = DiagnosticsHierarchy::new_root();
        b.add_missing(MissingValueReason::LinkNotFound, "a".to_string());
        a.merge(b);
        let expected = DiagnosticsHierarchy {
            missing: vec![MissingValue {
                reason: MissingValueReason::LinkNotFound,
                name: "a".to_string(),
            }],
            ..DiagnosticsHierarchy::new_root()
        };
        assert_eq!(a, expected);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_overwrite_property() {
        let mut a = DiagnosticsHierarchy::new(
            "root",
            vec![Property::String("x".to_string(), "foo".to_string())],
            vec![],
        );
        let b = DiagnosticsHierarchy::new(
            "root",
            vec![Property::String("x".to_string(), "bar".to_string())],
            vec![],
        );
        a.merge(b);
        let expected = DiagnosticsHierarchy::new(
            "root",
            vec![Property::String("x".to_string(), "bar".to_string())],
            vec![],
        );
        assert_eq!(a, expected);
    }

    #[fuchsia::test]
    fn test_merge_hierarchy_recursive_children() {
        let mut a = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![Property::Int("a".to_string(), 1)],
                vec![],
            )],
        );
        let b = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![Property::Int("b".to_string(), 2)],
                vec![],
            )],
        );
        a.merge(b);
        let expected = DiagnosticsHierarchy::new(
            "root",
            vec![],
            vec![DiagnosticsHierarchy::new(
                "child",
                vec![Property::Int("a".to_string(), 1), Property::Int("b".to_string(), 2)],
                vec![],
            )],
        );
        assert_eq!(a, expected);
    }
}