Move polyfills for !NET targets to src/libraries/Common/src/Polyfills/

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2

[EgorBo]

This allows us to pretend new APIs exist for .NET Standard 2.0/NETFX/etc targets and avoid #if NET else mess.

Description

• Moved downlevel polyfills into src/libraries/Common/src/Polyfills/ and updated multiple libraries to call "modern" APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.
• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable's System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.
• Moved src/libraries/Common/tests/System/Collections/DictionaryExtensions.cs into src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs to consolidate duplicate TryAdd implementations.
• Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/ for consistent directory structure; updated references in Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.
• Cached Environment.ProcessId in EnvironmentPolyfills using a static field to avoid creating and disposing a Process object on every access on downlevel TFMs.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-meta
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Moves downlevel polyfills into src/libraries/Common/src/Polyfills/ and updates multiple libraries to call the “modern” APIs unconditionally (e.g., Stopwatch.GetElapsedTime, double.IsFinite, Array.MaxLength), relying on polyfills for non-.NETCoreApp targets to reduce #if usage.

Changes:

• Replaced many #if NET / #else code paths with unified API calls and added corresponding polyfills via $(CommonPath)Polyfills\*.cs.
• Removed library-local polyfill helpers (e.g., JsonHelpers.IsFinite, System.Collections.Immutable’s System/Polyfills.cs) in favor of shared Common polyfills.
• Updated project files to link in the required polyfill sources for non-.NETCoreApp target frameworks.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/RateLimiterHelper.cs	Uses Stopwatch.GetElapsedTime unconditionally (polyfilled for downlevel).
src/libraries/System.Threading.RateLimiting/src/System.Threading.RateLimiting.csproj	Links StopwatchPolyfills.cs for non-.NETCoreApp builds.
src/libraries/System.Text.Json/src/System/Text/Json/Writer/JsonWriterHelper.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs	Switches finite checks to double.IsFinite / float.IsFinite.
src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.cs	Removes local IsFinite helpers and BitArray.HasAllSet polyfill.
src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs	Uses Array.MaxLength instead of hardcoded constant.
src/libraries/System.Text.Json/src/System.Text.Json.csproj	Links Double/Single/BitArray/Array polyfills for non-.NETCoreApp.
src/libraries/System.Speech/src/System.Speech.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Speech/src/Internal/Synthesis/EngineSite.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Speech/src/Internal/Synthesis/AudioBase.cs	Replaces manual read loop with Stream.ReadExactly.
src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj	Replaces in-project polyfills with linked Common BitConverter/Guid polyfills.
src/libraries/System.IO.Hashing/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs	Uses CopyToAsync(destination, cancellationToken) overload unconditionally (polyfilled downlevel).
src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj	Links StreamPolyfills.cs for non-.NETCoreApp.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/Writer/CborWriter.Tag.cs	Uses DateTimeOffset.TotalOffsetMinutes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System/Formats/Cbor/CborConformanceLevel.cs	Uses HashCode.AddBytes unconditionally (polyfilled downlevel).
src/libraries/System.Formats.Cbor/src/System.Formats.Cbor.csproj	Links DateTimeOffset/HashCode/Array polyfills for non-.NETCoreApp.
src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/Base2ExponentialHistogramAggregator.cs	Uses double.IsFinite directly; removes local helper.
src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj	Links DoublePolyfills.cs for non-.NETCoreApp.
src/libraries/System.Collections.Immutable/tests/System.Collections.Immutable.Tests.csproj	Replaces product-local polyfills include with linked Common polyfills in tests.
src/libraries/System.Collections.Immutable/src/System/Polyfills.cs	Removes library-local polyfills file.
src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenHashTable.cs	Uses Array.MaxLength unconditionally.
src/libraries/System.Collections.Immutable/src/System.Collections.Immutable.csproj	Removes System\Polyfills.cs; links Common polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs	Simplifies conditional IsAndroidOrAppleMobile expression body.
src/libraries/Microsoft.Extensions.Logging.Console/src/Microsoft.Extensions.Logging.Console.csproj	Links TextWriter/Encoding polyfills for non-.NETCoreApp.
src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs	Removes unsafe GetChars fallback in favor of polyfilled overloads; simplifies char handling.
src/libraries/Microsoft.Extensions.Logging.Console/src/AnsiParsingLogConsole.cs	Uses TextWriter.Write(ReadOnlySpan<char>) unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses Environment.ProcessId unconditionally (polyfilled downlevel).
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/Microsoft.Extensions.Hosting.Systemd.csproj	Links EnvironmentPolyfills.cs for non-.NETCoreApp.
src/libraries/Common/src/Polyfills/TextWriterPolyfills.cs	Adds downlevel TextWriter.Write(ReadOnlySpan<char>).
src/libraries/Common/src/Polyfills/StreamPolyfills.cs	Adds downlevel Stream.ReadExactly(byte[]) and CopyToAsync(Stream, CancellationToken).
src/libraries/Common/src/Polyfills/StopwatchPolyfills.cs	Adds downlevel Stopwatch.GetElapsedTime overloads.
src/libraries/Common/src/Polyfills/SinglePolyfills.cs	Adds downlevel float.IsFinite.
src/libraries/Common/src/Polyfills/DoublePolyfills.cs	Adds downlevel double.IsFinite.
src/libraries/Common/src/Polyfills/BitArrayPolyfills.cs	Adds downlevel BitArray.HasAllSet().
src/libraries/Common/src/Polyfills/ArrayPolyfills.cs	Adds downlevel Array.MaxLength.
src/libraries/Common/src/Polyfills/DateTimeOffsetPolyfills.cs	Adds downlevel DateTimeOffset.TotalOffsetMinutes.
src/libraries/Common/src/Polyfills/HashCodePolyfills.cs	Adds downlevel HashCode.AddBytes(ReadOnlySpan<byte>) as an extension method.
src/libraries/Common/src/Polyfills/EnvironmentPolyfills.cs	Adds downlevel Environment.ProcessId.
src/libraries/Common/src/Polyfills/GuidPolyfills.cs	Adds downlevel Guid.TryWriteBytes(Span<byte>).
src/libraries/Common/src/Polyfills/BitConverterPolyfills.cs	Adds downlevel BitConverter.SingleToUInt32Bits / DoubleToUInt64Bits.
src/libraries/Common/src/Polyfills/IReadOnlySetPolyfill.cs	Adds downlevel IReadOnlySet<T> (guarded by #if !NET).
src/libraries/Common/src/Polyfills/BitOperationsPolyfill.cs	Adds downlevel System.Numerics.BitOperations.RotateLeft (guarded by #if !NET).
src/libraries/Common/src/Polyfills/CollectionsPolyfills.cs	Adds downlevel KeyValuePair.Deconstruct extension method.
src/libraries/Common/src/Polyfills/DictionaryPolyfills.cs	Adds downlevel TryAdd / TryDequeue polyfills (new shared source).

[Copilot]

Pull request overview

Copilot reviewed 66 out of 66 changed files in this pull request and generated 2 comments.

[Copilot]

Observation — EncodingPolyfills.cs lives outside Polyfills/ directory
EncodingPolyfills.cs is at $(CommonPath)System\Text\EncodingPolyfills.cs (pre-existing file not moved by this PR) but is l...

Done in 0f64157. Moved EncodingPolyfills.cs from src/libraries/Common/src/System/Text/ to src/libraries/Common/src/Polyfills/, updated the file to use a file-scoped namespace, and updated the references in both Directory.Build.targets and Microsoft.Extensions.Logging.Console.csproj.

[EgorBo]

Ah, I was not aware it finally is able to push into developers' PRs 🙂 . Although, I guess it's possible only because my local Copilot filed this PR in dotnet/runtime and not in EgorBo/runtime

[jkotas]

Right, it works only for PRs in dotnet/runtime currently.

[jkotas]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exist. On .NETCoreApp the real property is used instead (zero-cost)

@copilot Address this feedback by adding a simple cache

[EgorBo]

@copilot Address this feedback by adding a simple cache

I wasn't sure it in and left it as is. Actually, my impl is even better than whatever we had before - we didn't even dispose process objects.

[Copilot]

The polyfill creates and disposes a Process object on every access. This matches the pattern used by the old inline #else code and only runs on downlevel TFMs where Environment.ProcessId doesn't exi...

Done in f0bf71e. Added a s_processId static field initialized to 0 (not a valid PID) as the cache sentinel — the Process object is now only created once per process lifetime.

[jkotas]

I wasn't sure it in and left it as is

I think we want to avoid bad surprises when using polyfills.

[EgorBo]

/ba-g deadletter (WasmTestOnV8)

[jkotas]

I have asked copilot to look for more https://github.com/dotnet/runtime/tasks/8e893e7e-9ea0-4c23-9402-5d3b9a8a0af2