Replace string.Compare == 0 patterns with Equals/StartsWith/AsSpan calls by Copilot · Pull Request #124566 · dotnet/runtime

Copilot · 2026-02-18T18:50:10Z

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Replace all instances of the verbose pattern: (q.Length >= keyword.Length) && (string.Compare(q, 0, keyword, 0, keyword.Length, StringComparison.OrdinalIgnoreCase) == 0) and its != 0 / 0 != variants with the simpler: q.StartsWith(keyword, StringComparison.OrdinalIgnoreCase) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Replace string.Compare == 0 / != 0 patterns with more idiomatic Equals, StartsWith, and AsSpan alternatives across System.Net libraries. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…sWith/AsSpan in remaining source files Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyQualifiedToken.cs

…ls(..., Ordinal) Co-authored-by: EgorBo <523221+EgorBo@users.noreply.github.com>

src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/StringUtil.cs

MihaZupan

@copilot Address all comments. For any suggestions that point at more patterns that can be switched, look for more places where they could apply to

...es/System.ComponentModel.TypeConverter/src/System/ComponentModel/ComponentResourceManager.cs

src/libraries/System.DirectoryServices/src/System/DirectoryServices/ActiveDirectory/Utils.cs

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpConnection.Auth.cs

src/libraries/System.Private.CoreLib/src/System/Globalization/HijriCalendar.Win32.cs

src/libraries/System.Private.Xml.Linq/src/System/Xml/Linq/XNamespace.cs

src/libraries/System.Private.Xml/src/System/Xml/Schema/XdrBuilder.cs

src/libraries/System.Private.Xml/src/System/Xml/XPath/Internal/StringFunctions.cs

src/libraries/System.Private.Xml/src/System/Xml/Xsl/Runtime/XsltFunctions.cs

src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/FileChangeNotificationSystem.cs

dotnet-policy-service · 2026-02-18T22:27:07Z

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…dant length checks Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

Copilot · 2026-02-18T22:33:42Z

@copilot Address all comments. For any suggestions that point at more patterns that can be switched, look for more places where they could apply to

All comments addressed in 9479aff: null safety fixes in StringUtil and HijriCalendar, simplified ComponentResourceManager/DirectoryServices patterns, replaced the remaining string.Compare in SmtpConnection.Auth, and removed redundant length checks across 8 files (SecurityElement, EnumDataContract, XHashtable, XNamespace, XdrBuilder, StringFunctions, XsltFunctions, FileChangeNotificationSystem).

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- Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.deps.json /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/testhost.dll --port 38909 --endpoint 127.0.0.1:038909 --role client --parentprocessid 30451 --datacollectionport 41653 --telemetryoptedin false DTARGET_64BIT -D--others (dns block)
5d0fddfa8dd54859a60706f04b1d4959
- Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.deps.json /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/testhost.dll --port 38909 --endpoint 127.0.0.1:038909 --role client --parentprocessid 30451 --datacollectionport 41653 --telemetryoptedin false DTARGET_64BIT -D--others (dns block)
69ff98bbf1924634b93257023b62350c
- Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.deps.json /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/testhost.dll --port 38909 --endpoint 127.0.0.1:038909 --role client --parentprocessid 30451 --datacollectionport 41653 --telemetryoptedin false DTARGET_64BIT -D--others (dns block)
7c833bcc974149418852f0abe1a379f5
- Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.deps.json /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/testhost.dll --port 38909 --endpoint 127.0.0.1:038909 --role client --parentprocessid 30451 --datacollectionport 41653 --telemetryoptedin false DTARGET_64BIT -D--others (dns block)
f435685089c74e0790afa87f227ebca2
- Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/System.Net.Mail.Functional.Tests.deps.json /home/REDACTED/work/runtime/runtime/artifacts/bin/System.Net.Mail.Functional.Tests/Debug/net11.0-unix/testhost.dll --port 38909 --endpoint 127.0.0.1:038909 --role client --parentprocessid 30451 --datacollectionport 41653 --telemetryoptedin false DTARGET_64BIT -D--others (dns block)

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MihaZupan

@copilot Address the last comments

src/libraries/System.Private.CoreLib/src/System/Globalization/IdnMapping.cs

src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/FileChangeNotificationSystem.cs

…n FileChangeNotificationSystem.cs Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

Copilot

Pull request overview

This pull request systematically replaces verbose string.Compare(...) == 0 / != 0 patterns with more idiomatic and performant alternatives across the codebase. The changes improve code readability and maintainability by using appropriate methods like Equals, StartsWith, EndsWith, and span-based comparisons.

Changes:

Replace equality checks using string.Compare(...) == 0 with string.Equals() or direct equality operators
Replace prefix checks using string.Compare(str, 0, prefix, 0, length) == 0 with StartsWith() or AsSpan().StartsWith()
Replace suffix checks with EndsWith() methods
Simplify substring comparisons using AsSpan().Equals() for better performance
Add appropriate null checks where needed (e.g., HijriCalendar, SmtpConnection, StringUtil)

Reviewed changes

Copilot reviewed 34 out of 34 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
RuntimeModuleBuilder.Mono.cs	Replace case-insensitive Compare with Equals using InvariantCultureIgnoreCase
FileChangeNotificationSystem.cs	Simplify length check and comparison to single Equals call
XsltFunctions.cs	Replace substring comparison with StartsWith for prefix checking
StringFunctions.cs	Replace substring comparison with StartsWith for prefix checking
XdrBuilder.cs	Replace substring comparison with StartsWith, remove redundant length check
XNamespace.cs	Use AsSpan().Equals() for substring comparison with special namespace constants
XHashtable.cs	Use AsSpan().Equals() for key comparison in hash table lookup
EnumDataContract.cs	Use AsSpan().Equals() for enum member name matching
SecurityElement.cs	Replace substring comparison with AsSpan().StartsWith() for escape sequence detection
IdnMapping.cs	Replace ACE prefix check with AsSpan().StartsWith() (preserves short-circuit behavior)
HijriCalendar.Win32.cs	Add null check and use StartsWith for registry key prefix matching
Environment.GetFolderPathCore.Unix.cs	Replace substring comparisons with AsSpan().StartsWith() for XDG directory parsing
WebProxy.NonWasm.cs	Replace substring comparison with AsSpan().Equals() for domain name matching
SmtpConnection.Auth.cs	Add null check and replace multiple substring comparisons with StartsWith
HttpListener.Windows.cs	Replace authentication header comparisons with AsSpan().Equals()
HttpListenerContext.Managed.cs	Replace Basic auth header check with AsSpan().Equals()
HttpListener.cs	Replace URL scheme checks with StartsWith for http:// and https://
HttpWindowsProxy.cs	Replace proxy bypass string checks with AsSpan().StartsWith()
AuthenticationHeaderValue.cs	Use AsSpan().Equals() for authentication scheme comparison
ManagementQuery.cs	Replace 32+ occurrences of keyword matching with StartsWith calls
Utils.cs (DirectoryServices)	Simplify character comparison and use AsSpan().StartsWith() for property name matching
EventLog.cs	Replace substring comparison with AsSpan().Equals() for event source validation
OdbcUtils.cs	Use AsSpan().StartsWith() for SQL token matching
DataTable.cs	Replace suffix comparisons with EndsWith for " ASC" and " DESC" detection
UrlPath.cs	Use AsSpan().Equals() for case-insensitive path comparison
StringUtil.cs	Add null checks and use StartsWith for both ordinal and ignore-case variants
AppSettingsReader.cs	Use AsSpan().Equals() for substring comparison in null string detection
ReflectPropertyDescriptor.cs	Replace case-insensitive Compare with Equals for property name matching
DesignerOptionService.cs	Replace case-insensitive Compare with Equals for child collection lookup
ComponentResourceManager.cs	Simplify if/else logic to single StartsWith with conditional StringComparison
CredentialCacheKey.cs	Use AsSpan().Equals() for URI prefix path comparison
Program.cs (dotnet-pgo)	Replace file extension comparisons with string.Equals
AssemblyQualifiedToken.cs	Use direct string equality operator instead of CompareOrdinal
EcmaModule.Sorting.cs	Use StringComparer.Equals in assertion instead of Compare != 0

Rob-Hague · 2026-02-20T08:36:18Z

An outsider might imagine that AI would be put to better use by improving CA2251, if these cases are not already caught by it

Initial plan

33965e2

Copilot AI assigned Copilot and MihaZupan Feb 18, 2026

Copilot started work on behalf of MihaZupan February 18, 2026 18:50 View session

github-actions bot added the area-Infrastructure label Feb 18, 2026

github-project-automation bot added this to Runtime Infra Feb 18, 2026

Copilot AI and others added 3 commits February 18, 2026 19:24

Replace string.Compare patterns with Equals/StartsWith/AsSpan

28cc12b

Replace string.Compare == 0 / != 0 patterns with more idiomatic Equals, StartsWith, and AsSpan alternatives across System.Net libraries. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Replace string.Compare/CompareOrdinal == 0 patterns with Equals/Start…

bef5506

…sWith/AsSpan in remaining source files Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Refactor string comparison logic to use Equals method~~ Replace string.Compare == 0 patterns with Equals/StartsWith/AsSpan calls Feb 18, 2026

Copilot finished work on behalf of MihaZupan February 18, 2026 19:44

Copilot AI requested a review from MihaZupan February 18, 2026 19:44

EgorBo reviewed Feb 18, 2026

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src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyQualifiedToken.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of EgorBo February 18, 2026 20:30 View session

Simplify AssemblyQualifiedToken.Equals: use == instead of string.Equa…

03cf274

…ls(..., Ordinal) Co-authored-by: EgorBo <523221+EgorBo@users.noreply.github.com>

Copilot AI requested a review from EgorBo February 18, 2026 20:34

Copilot finished work on behalf of EgorBo February 18, 2026 20:34

GrabYourPitchforks reviewed Feb 18, 2026

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src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/StringUtil.cs Show resolved Hide resolved

MihaZupan reviewed Feb 18, 2026

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Copilot started work on behalf of MihaZupan February 18, 2026 22:03 View session

MihaZupan added area-Meta and removed area-Infrastructure labels Feb 18, 2026

Address review feedback: null checks, simplify patterns, remove redun…

9479aff

…dant length checks Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

Copilot AI requested a review from MihaZupan February 18, 2026 22:33

Copilot finished work on behalf of MihaZupan February 18, 2026 22:33

MihaZupan reviewed Feb 18, 2026

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src/libraries/System.Private.CoreLib/src/System/Globalization/IdnMapping.cs Outdated Show resolved Hide resolved

src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/FileChangeNotificationSystem.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of MihaZupan February 18, 2026 22:43 View session

Remove redundant length check in IdnMapping.cs, use instance Equals i…

523b252

…n FileChangeNotificationSystem.cs Co-authored-by: MihaZupan <25307628+MihaZupan@users.noreply.github.com>

Copilot AI requested a review from MihaZupan February 18, 2026 22:47

Copilot finished work on behalf of MihaZupan February 18, 2026 22:47

MihaZupan added this to the 11.0.0 milestone Feb 18, 2026

MihaZupan approved these changes Feb 18, 2026

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MihaZupan marked this pull request as ready for review February 18, 2026 22:48

MihaZupan requested a review from steveisok as a code owner February 18, 2026 22:48

Copilot AI review requested due to automatic review settings February 18, 2026 22:48

MihaZupan requested review from MichalStrehovsky and vitek-karas as code owners February 18, 2026 22:48

Copilot started reviewing on behalf of MihaZupan February 18, 2026 22:49 View session

Copilot AI reviewed Feb 18, 2026

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MihuBot mentioned this pull request Feb 18, 2026

[JitDiff X64] [Copilot] Replace string.Compare == 0 patterns with Equals/Sta ... MihuBot/runtime-utils#1772

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build-analysis bot mentioned this pull request Feb 19, 2026

[android][clr] No peer certificates when executing System.Net.Http.Functional.Tests on Android emulator #124526

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MihaZupan enabled auto-merge (squash) February 19, 2026 15:12

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Pull request overview

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Rob-Hague commented Feb 20, 2026

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Copilot AI commented Feb 18, 2026 •

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