Simplify duplication in IConfigurationSource (#6386)

## Summary of changes

- Delete legacy `IConfigurationSource`
- Rename `ITelmeteredConfigurationSource` => `IConfigurationSource`
- Remove some "public" API workarounds
- Make some APIs `public` instead of `internal` (just to satisfy
compiler)
- Fix tests

## Reason for change

`ITelmeteredConfigurationSource` was introduced when
`IConfigurationSource` was public, and so could not be changed. We have
since removed that interface from the public API (it's not in
`Datadog.trace.Manual`) so now it simply adds confusion and complexity
(as it should _not_ be used internally in Datadog.Trace).

## Implementation details

This PR looks more complex than it is, because in order to replace all
the usages of the old `IConfigurationSource` with the new one, I had to
mark some other APIs public (and document them to satisfy the
analyzers).

It is mostly

- Delete legacy `IConfigurationSource`
- Rename `ITelmeteredConfigurationSource` => `IConfigurationSource`
- Fix any errors

I took the opportunity to also remove some of the `*Internal` methods
which were used to avoid calling the "public" APIs; seeing as these
aren't _actually_ public any more, that's just unnecessary duplication.

## Test coverage

The testing was a pain. The `ConfigurationBuilder` tests were all
designed to check that `ITelmeteredConfigurationSource` gave the same
results as `IConfigurationSource` (while never _explicitly_ specifying
what the "expected" behaviour was. I took some time to enumerate the
_actual_ expected values for the `NameValueCollection` source, but the
`Json` source has very different behaviour that is more of a pain to
test, so I chose to simplify a lot there. We could do a _lot_ to clean
up those tests, but I didn't want to add even more complexity in this
PR.

## Other details

To help "fix" the ASM tests I introduced a
`DictionaryObjectConfigurationSource`, in which you pass in a
`Dictionary<string, object>`. This is useful for testing (as it was
previously used) but is actually going to be useful for a future
clean-up PR too, so I kept it in Datadog.Trace instead of in the test
project.

Part of stack 
- #6370
- #6376
- #6385
- #6386 👈 This PR
- #6397
- #6399
- #6400
- #6405
- #6408

Author: andrewlock

tracer/src/Datadog.Trace.Tools.Runner/Utils.cs

@@ -402,9 +402,9 @@ public static string GetEnvironmentVariable(string key, string defaultValue = nu
                 env[ConfigurationKeys.AgentUri] = agentUrl;
             }
 
-            var configurationSource = new CompositeConfigurationSourceInternal();
-            configurationSource.AddInternal(new NameValueConfigurationSource(env, ConfigurationOrigins.EnvVars));
-            configurationSource.AddInternal(GlobalConfigurationSource.Instance);
+            var configurationSource = new CompositeConfigurationSource();
+            configurationSource.Add(new NameValueConfigurationSource(env, ConfigurationOrigins.EnvVars));
+            configurationSource.Add(GlobalConfigurationSource.Instance);
 
             var tracerSettings = new TracerSettings(configurationSource, new ConfigurationTelemetry(), new OverrideErrorLog());
             var settings = new ImmutableTracerSettings(tracerSettings, unusedParamNotToUsePublicApi: true);

tracer/src/Datadog.Trace/Ci/Configuration/CIVisibilitySettings.cs

@@ -301,13 +301,13 @@ private TracerSettings InitializeTracerSettings()
         {
             var source = GlobalConfigurationSource.CreateDefaultConfigurationSource();
             var defaultExcludedUrlSubstrings = string.Empty;
-            var configResult = ((ITelemeteredConfigurationSource)source).GetString(ConfigurationKeys.HttpClientExcludedUrlSubstrings, NullConfigurationTelemetry.Instance, validator: null, recordValue: false);
+            var configResult = source.GetString(ConfigurationKeys.HttpClientExcludedUrlSubstrings, NullConfigurationTelemetry.Instance, validator: null, recordValue: false);
             if (configResult is { IsValid: true, Result: { } substrings } && !string.IsNullOrWhiteSpace(substrings))
             {
                 defaultExcludedUrlSubstrings = substrings + ", ";
             }
 
-            source.InsertInternal(0, new NameValueConfigurationSource(
+            source.Insert(0, new NameValueConfigurationSource(
                                       new NameValueCollection
                                       {
                                           [ConfigurationKeys.HttpClientExcludedUrlSubstrings] = defaultExcludedUrlSubstrings + "/session/FakeSessionIdForPollingPurposes",

tracer/src/Datadog.Trace/Configuration/ConfigurationSources/CompositeConfigurationSource.cs

@@ -21,211 +21,82 @@ namespace Datadog.Trace.Configuration
     /// <summary>
     /// Represents one or more configuration sources.
     /// </summary>
-    public class CompositeConfigurationSource : IConfigurationSource, IEnumerable<IConfigurationSource>, ITelemeteredConfigurationSource
+    internal class CompositeConfigurationSource : IConfigurationSource, IEnumerable<IConfigurationSource>
     {
-        private readonly List<ITelemeteredConfigurationSource> _sources = new();
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="CompositeConfigurationSource"/> class.
-        /// </summary>
-        [PublicApi]
-        public CompositeConfigurationSource()
-        {
-            TelemetryFactory.Metrics.Record(PublicApiUsage.CompositeConfigurationSource_Ctor);
-        }
-
-        private protected CompositeConfigurationSource(bool unusedParamNotToUsePublicApi)
-        {
-            // unused parameter is to give us a non-public API we can use
-        }
+        private readonly List<IConfigurationSource> _sources = new();
 
         /// <summary>
         /// Adds a new configuration source to this instance.
         /// </summary>
         /// <param name="source">The configuration source to add.</param>
-        [PublicApi]
         public void Add(IConfigurationSource source)
         {
-            TelemetryFactory.Metrics.Record(PublicApiUsage.CompositeConfigurationSource_Add);
             if (source == null) { ThrowHelper.ThrowArgumentNullException(nameof(source)); }
 
-            AddInternal(source);
+            _sources.Add(source);
         }
 
         /// <summary>
-        /// Inserts an element into the <see cref="CompositeConfigurationSource"/> at the specified index.
+        /// Inserts an element into the <see cref="Datadog.Trace.Configuration.CompositeConfigurationSource"/> at the specified index.
         /// </summary>
         /// <param name="index">The zero-based index at which <paramref name="item"/> should be inserted.</param>
         /// <param name="item">The configuration source to insert.</param>
-        [PublicApi]
         public void Insert(int index, IConfigurationSource item)
         {
-            TelemetryFactory.Metrics.Record(PublicApiUsage.CompositeConfigurationSource_Insert);
             if (item == null) { ThrowHelper.ThrowArgumentNullException(nameof(item)); }
 
-            InsertInternal(index, item);
-        }
-
-        /// <summary>
-        /// Gets the <see cref="string"/> value of the first setting found with
-        /// the specified key from the current list of configuration sources.
-        /// Sources are queried in the order in which they were added.
-        /// </summary>
-        /// <param name="key">The key that identifies the setting.</param>
-        /// <returns>The value of the setting, or <c>null</c> if not found.</returns>
-        [PublicApi]
-        public string? GetString(string key)
-        {
-            var value = _sources
-                  .Select(source => source.GetString(key, NullConfigurationTelemetry.Instance, validator: null, recordValue: true))
-                  .FirstOrDefault(value => value.IsValid, ConfigurationResult<string>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
-
-        /// <summary>
-        /// Gets the <see cref="int"/> value of the first setting found with
-        /// the specified key from the current list of configuration sources.
-        /// Sources are queried in the order in which they were added.
-        /// </summary>
-        /// <param name="key">The key that identifies the setting.</param>
-        /// <returns>The value of the setting, or <c>null</c> if not found.</returns>
-        [PublicApi]
-        public int? GetInt32(string key)
-        {
-            var value = _sources
-                       .Select(source => source.GetInt32(key, NullConfigurationTelemetry.Instance, validator: null))
-                       .FirstOrDefault(value => value.IsValid, ConfigurationResult<int>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
-
-        /// <summary>
-        /// Gets the <see cref="double"/> value of the first setting found with
-        /// the specified key from the current list of configuration sources.
-        /// Sources are queried in the order in which they were added.
-        /// </summary>
-        /// <param name="key">The key that identifies the setting.</param>
-        /// <returns>The value of the setting, or <c>null</c> if not found.</returns>
-        [PublicApi]
-        public double? GetDouble(string key)
-        {
-            var value = _sources
-                       .Select(source => source.GetDouble(key, NullConfigurationTelemetry.Instance, validator: null))
-                       .FirstOrDefault(value => value.IsValid, ConfigurationResult<double>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
-
-        /// <summary>
-        /// Gets the <see cref="bool"/> value of the first setting found with
-        /// the specified key from the current list of configuration sources.
-        /// Sources are queried in the order in which they were added.
-        /// </summary>
-        /// <param name="key">The key that identifies the setting.</param>
-        /// <returns>The value of the setting, or <c>null</c> if not found.</returns>
-        [PublicApi]
-        public bool? GetBool(string key)
-        {
-            var value = _sources
-                       .Select(source => source.GetBool(key, NullConfigurationTelemetry.Instance, validator: null))
-                       .FirstOrDefault(value => value.IsValid, ConfigurationResult<bool>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
-
-        internal void AddInternal(IConfigurationSource source)
-        {
-            var telemeteredSource = source as ITelemeteredConfigurationSource ?? new CustomTelemeteredConfigurationSource(source);
-            _sources.Add(telemeteredSource);
-        }
-
-        internal void InsertInternal(int index, IConfigurationSource source)
-        {
-            var telemeteredSource = source as ITelemeteredConfigurationSource ?? new CustomTelemeteredConfigurationSource(source);
-            _sources.Insert(index, telemeteredSource);
-        }
-
-        /// <inheritdoc />
-        [PublicApi]
-        IEnumerator<IConfigurationSource> IEnumerable<IConfigurationSource>.GetEnumerator()
-        {
-            return _sources
-                  .Select(
-                       x => x as IConfigurationSource
-                         ?? ((CustomTelemeteredConfigurationSource)x).Source)
-                  .GetEnumerator();
-        }
-
-        /// <inheritdoc />
-        [PublicApi]
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return _sources
-                  .Select(
-                       x => x as IConfigurationSource
-                         ?? ((CustomTelemeteredConfigurationSource)x).Source)
-                  .GetEnumerator();
+            _sources.Insert(index, item);
         }
 
         /// <inheritdoc />
-        [PublicApi]
-        public IDictionary<string, string>? GetDictionary(string key)
-        {
-            var value = _sources
-                       .Select(source => source.GetDictionary(key, NullConfigurationTelemetry.Instance, validator: null))
-                       .FirstOrDefault(value => value.IsValid, ConfigurationResult<IDictionary<string, string>>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
+        IEnumerator<IConfigurationSource> IEnumerable<IConfigurationSource>.GetEnumerator() => _sources.GetEnumerator();
 
         /// <inheritdoc />
         [PublicApi]
-        public IDictionary<string, string>? GetDictionary(string key, bool allowOptionalMappings)
-        {
-            var value = _sources
-                       .Select(source => source.GetDictionary(key, NullConfigurationTelemetry.Instance, validator: null, allowOptionalMappings, separator: ':'))
-                       .FirstOrDefault(value => value.IsValid, ConfigurationResult<IDictionary<string, string>>.NotFound());
-            return value.IsValid ? value.Result : null;
-        }
+        IEnumerator IEnumerable.GetEnumerator() => _sources.GetEnumerator();
 
         /// <inheritdoc />
-        bool ITelemeteredConfigurationSource.IsPresent(string key)
+        public bool IsPresent(string key)
             => _sources.Select(source => source.IsPresent(key)).FirstOrDefault(value => value);
 
         /// <inheritdoc />
-        ConfigurationResult<string> ITelemeteredConfigurationSource.GetString(string key, IConfigurationTelemetry telemetry, Func<string, bool>? validator, bool recordValue)
+        public ConfigurationResult<string> GetString(string key, IConfigurationTelemetry telemetry, Func<string, bool>? validator, bool recordValue)
             => _sources
               .Select(source => source.GetString(key, telemetry, validator, recordValue))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<string>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<int> ITelemeteredConfigurationSource.GetInt32(string key, IConfigurationTelemetry telemetry, Func<int, bool>? validator)
+        public ConfigurationResult<int> GetInt32(string key, IConfigurationTelemetry telemetry, Func<int, bool>? validator)
             => _sources
               .Select(source => source.GetInt32(key, telemetry, validator))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<int>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<double> ITelemeteredConfigurationSource.GetDouble(string key, IConfigurationTelemetry telemetry, Func<double, bool>? validator)
+        public ConfigurationResult<double> GetDouble(string key, IConfigurationTelemetry telemetry, Func<double, bool>? validator)
             => _sources
               .Select(source => source.GetDouble(key, telemetry, validator))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<double>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<bool> ITelemeteredConfigurationSource.GetBool(string key, IConfigurationTelemetry telemetry, Func<bool, bool>? validator)
+        public ConfigurationResult<bool> GetBool(string key, IConfigurationTelemetry telemetry, Func<bool, bool>? validator)
             => _sources
               .Select(source => source.GetBool(key, telemetry, validator))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<bool>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<IDictionary<string, string>> ITelemeteredConfigurationSource.GetDictionary(string key, IConfigurationTelemetry telemetry, Func<IDictionary<string, string>, bool>? validator)
+        public ConfigurationResult<IDictionary<string, string>> GetDictionary(string key, IConfigurationTelemetry telemetry, Func<IDictionary<string, string>, bool>? validator)
             => _sources
               .Select(source => source.GetDictionary(key, telemetry, validator))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<IDictionary<string, string>>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<IDictionary<string, string>> ITelemeteredConfigurationSource.GetDictionary(string key, IConfigurationTelemetry telemetry, Func<IDictionary<string, string>, bool>? validator, bool allowOptionalMappings, char separator)
+        public ConfigurationResult<IDictionary<string, string>> GetDictionary(string key, IConfigurationTelemetry telemetry, Func<IDictionary<string, string>, bool>? validator, bool allowOptionalMappings, char separator)
             => _sources
               .Select(source => source.GetDictionary(key, telemetry, validator, allowOptionalMappings, separator))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<IDictionary<string, string>>.NotFound());
 
         /// <inheritdoc />
-        ConfigurationResult<T> ITelemeteredConfigurationSource.GetAs<T>(string key, IConfigurationTelemetry telemetry, Func<string, ParsingResult<T>> converter, Func<T, bool>? validator, bool recordValue)
+        public ConfigurationResult<T> GetAs<T>(string key, IConfigurationTelemetry telemetry, Func<string, ParsingResult<T>> converter, Func<T, bool>? validator, bool recordValue)
             => _sources
               .Select(source => source.GetAs<T>(key, telemetry, converter, validator, recordValue))
               .FirstOrDefault(value => value.IsValid, ConfigurationResult<T>.NotFound());

tracer/src/Datadog.Trace/Configuration/ConfigurationSources/CompositeConfigurationSourceInternal.cs

@@ -21,7 +21,7 @@ public DictionaryConfigurationSource(IReadOnlyDictionary<string, string> diction
 
     internal override ConfigurationOrigins Origin => ConfigurationOrigins.Code;
 
-    public override string? GetString(string key)
+    protected override string? GetString(string key)
     {
         _dictionary.TryGetValue(key, out var value);
         return value;