Add CA2027 analyzer to detect redundant Regex.IsMatch guard before Regex.Match

[Copilot]

Implementation Complete: CA2027 Analyzer for Redundant Regex.IsMatch Guard

Summary

Successfully implemented analyzer CA2027 with all code review feedback addressed.

Problem Pattern Detected

if (Regex.IsMatch(input, pattern))
{
    Match m = Regex.Match(input, pattern);
    ...
}

Latest Changes (This Commit)

Code Simplifications:

1. Merged FindMatchCallInBranch and FindMatchCallRecursive into a single recursive method - the separate wrapper was unnecessary
2. Removed increment/decrement operation checks from HasAssignmentToSymbol - not relevant for string arguments used in Regex methods

Benefits:

• Cleaner, more straightforward code
• Removed unnecessary abstraction layer
• More accurate dataflow analysis (no false checks for operations that can't apply to strings)

Test Results:
✅ All 26 tests passing
✅ Zero regressions
✅ All feedback addressed

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Analyzer]: Regex.IsMatch guarding Regex.Match</issue_title>
<issue_description>In looking through various code bases, I've seen the following pattern repeatedly:

if (Regex.IsMatch(pattern))
{
    Match m = Regex.Match(pattern);
    ...
}

That just doubles the work involved when there is a match. It should instead be:

if (Regex.Match(pattern) is { Success: true } m)
{
    ...
}

or something similar. We should have an analyzer that flags these duplicative guards and a fixer that transforms into something like the latter.
</issue_description>

<agent_instructions>Implement an analyzer and fixer in the Microsoft.CodeAnalysis.NetAnalyzers project, following the same approach and style as is used in the rest of the project. (Note that there's a pending PR open that adds a CA2026, so don't use that same ID.)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes dotnet/runtime#111239

---

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[stephentoub]

@copilot, there are build failures:

  One or more auto-generated documentation files were either edited manually, or not updated. Please revert changes made to the following files (if manually edited) and run `msbuild /t:pack` at the root of the repo to automatically update them:
      D:\a\_work\1\s\src\Microsoft.CodeAnalysis.NetAnalyzers\src\Microsoft.CodeAnalysis.NetAnalyzers.md
      D:\a\_work\1\s\src\Microsoft.CodeAnalysis.NetAnalyzers\src\Microsoft.CodeAnalysis.NetAnalyzers.sarif

[Copilot]

@copilot, there are build failures:

  One or more auto-generated documentation files were either edited manually, or not updated. Please revert changes made to the following files (if manually e...

Fixed by regenerating the auto-generated documentation files. The files now contain the updated CA2027 descriptions with the corrected resource strings.

[Copilot]

Pull Request Overview

This PR implements analyzer CA2027 to detect redundant Regex.IsMatch guard patterns before Regex.Match calls. The analyzer identifies cases where developers unnecessarily check Regex.IsMatch before calling Regex.Match with the same arguments, which duplicates the matching operation and impacts performance.

Key changes include:

• New analyzer that detects both standard guard patterns (if (IsMatch) { Match... }) and inverted early-return patterns (if (!IsMatch) { return; } Match...)
• Language-specific code fixers for C# and Visual Basic that remove redundant guards
• Comprehensive test coverage with 14 test cases covering various scenarios including dataflow analysis to prevent false positives

Reviewed Changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
AvoidRedundantRegexIsMatchBeforeMatch.cs	Core analyzer implementation with pattern detection and dataflow analysis
CSharpAvoidRedundantRegexIsMatchBeforeMatch.Fixer.cs	C# code fixer that transforms guard patterns to use Match().Success
BasicAvoidRedundantRegexIsMatchBeforeMatch.Fixer.vb	Visual Basic code fixer for removing redundant guards
AvoidRedundantRegexIsMatchBeforeMatchTests.cs	Comprehensive test suite covering positive/negative cases and edge scenarios
MicrosoftNetCoreAnalyzersResources.resx	Resource strings for analyzer messages and descriptions
DiagnosticCategoryAndIdRanges.txt	Updated rule ID range to include CA2027
AnalyzerReleases.Unshipped.md	Added CA2027 to unshipped analyzer releases
Multiple .xlf files	Localization files with new resource strings marked for translation
Microsoft.CodeAnalysis.NetAnalyzers.md/.sarif	Auto-generated documentation files