Polyfill span.Contains(T) #123656
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Polyfill span.Contains(T) #123656
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This was referenced Jan 27, 2026
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src/libraries/System.CodeDom/src/Microsoft/CSharp/CSharpCodeGenerator.cs
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...raries/System.Configuration.ConfigurationManager/src/System/Configuration/StringValidator.cs
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Pull request overview
This pull request adds polyfills for Contains(T) methods on ReadOnlySpan<T> and introduces corresponding Contains(char), StartsWith(char), and EndsWith(char) extension methods for strings to support downlevel targets (primarily .NET Standard 2.0 and .NET Framework).
Changes:
- Adds
StringPolyfills.cswith extension methods forstring.Contains(char),string.StartsWith(char), andstring.EndsWith(char)for pre-.NET Standard 2.1 targets - Adds
ReadOnlySpan<T>.Contains(T)polyfill toMemoryExtensionsPolyfills.cs - Converts numerous
IndexOfchecks throughout the codebase to use the more readableContains,StartsWith, andEndsWithmethods - Removes CA warning suppressions (CA1866, CA2249, CA1865, CA1867) that are no longer needed after the conversions
- Adds
IncludeSpanPolyfillsproperty to projects targeting downlevel frameworks
Reviewed changes
Copilot reviewed 74 out of 74 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| src/libraries/Common/src/System/StringPolyfills.cs | New polyfill file providing Contains(char), StartsWith(char), and EndsWith(char) for strings |
| src/libraries/Common/src/System/MemoryExtensionsPolyfills.cs | Adds Contains<T> polyfill for ReadOnlySpan<T> |
| src/libraries/Directory.Build.targets | Includes StringPolyfills.cs in the IncludeSpanPolyfills build configuration |
| src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/GenerateWasmBootJson.cs | Converts StartsWith("v") to StartsWith('v') |
| src/tasks/Crossgen2Tasks/RunReadyToRunCompiler.cs | Converts IndexOf("warning:") != -1 to Contains("warning:") |
| src/tasks/Crossgen2Tasks/CommonFilePulledFromSdkRepo/NuGetUtils.NuGet.cs | Converts IndexOf checks to Contains |
| src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/TypeNameBuilder.cs | Converts IndexOf(c) != -1 to Contains(c) for span |
| src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreter.cs | Converts IndexOf < 0 to !Contains for span |
| src/libraries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteValues.Comment.cs | Converts IndexOf checks, one using Contains with StringComparison |
| src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/EnumConverter.cs | Converts IndexOf(',') >= 0 to Contains(',') |
| src/libraries/System.Text.Json/src/System/Text/Json/Reader/*.cs | Multiple conversions of IndexOf delimiter checks to Contains |
| src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.cs | Converts IndexOf check to Contains |
| src/libraries/System.Speech/src/Result/RecognizedPhrase.cs | Converts Contains("$") to Contains('$') |
| src/libraries/System.Speech/src/Internal/SrgsParser/XmlParser.cs | BUG: Converts to ContainsAny without .AsSpan() call |
| src/libraries/System.ServiceProcess.ServiceController/src/System/ServiceProcess/ServiceController.cs | Converts StartsWith and Contains checks, removes outdated comment |
| src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/Aes.cs | Converts IndexOfAnyExcept >= 0 to ContainsAnyExcept |
| src/libraries/System.Runtime.InteropServices.JavaScript/gen/JSImportGenerator/*.cs | Converts IndexOf("<") to IndexOf('<') |
| src/libraries/System.Reflection.MetadataLoadContext/src/System/Reflection/TypeLoading/*.cs | Converts Contains checks and removes #if NET conditionals |
| src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/SseParser_1.cs | Converts IndexOf < 0 to !Contains |
| src/libraries/System.Memory/src/System/Buffers/SequenceReader.Search.cs | Converts IndexOf != -1 to Contains in loop condition |
| src/libraries/System.Management/src/System/Management/*.cs | Converts IndexOfAny and StartsWith checks |
| src/libraries/System.IO.Packaging/src/System/IO/Packaging/*.cs | Converts Contains checks and removes #if NET conditionals |
| src/libraries/System.DirectoryServices*/src/**/*.cs | Converts StartsWith and Contains checks |
| src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessManager.Windows.cs | Optimizes EndsWith(".") to direct character comparison |
| src/libraries/System.Data./src/**/.cs | Multiple conversions removing comments about .NET Core 2.1 availability |
| src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/StringValidator.cs | BUG: Changes field type to SearchValues but still formats it as string in error message |
| src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/*.cs | Multiple conversions and removal of #if NET conditionals |
| src/libraries/System.CodeDom/src/Microsoft/**/*.cs | Converts Contains checks and removes #if NET conditionals |
| src/libraries/Microsoft.Extensions./src/**/.cs | Multiple conversions and conditional removal |
| src/libraries/Common/src/**/*.cs | Multiple conversions in common code |
| src/coreclr/tools//src/**/.cs | Multiple conversions and warning suppressions removed |
| Multiple .csproj files | Removes CA warning suppressions and adds IncludeSpanPolyfills/polyfill references |
...raries/System.Configuration.ConfigurationManager/src/System/Configuration/StringValidator.cs
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