Fix SYSLIB1045 code fixer generating duplicate MyRegex names across partial class declarations by danmoseley · Pull Request #124698 · dotnet/runtime

danmoseley · 2026-02-21T04:37:17Z

Problem

When the SYSLIB1045 BatchFixer applies multiple code fixes concurrently to separate partial class declarations, each fix independently checks existing members via the semantic model. Since all fixers see the original compilation (before any fix is applied), they all conclude MyRegex is available and generate duplicate property names, causing CS0756.

Fix

In UpgradeToGeneratedRegexCodeFixer.CreateGeneratedRegexProperty, after finding the first available name via the semantic model, the new CountPrecedingRegexCallSites helper scans all DeclaringSyntaxReferences of the containing type for Regex constructor/static-method call sites that would also generate new property names. These are sorted deterministically (by file path, then span position). The current node's index in that sorted list determines how many names to skip, giving each concurrent fixer a unique name.

Test

Added CodeFixerGeneratesUniqueNamesAcrossPartialClassDeclarations — two new Regex(...) calls in separate partial class declarations of the same type, verifying MyRegex and MyRegex1 are generated. Verified the test fails without the fix (both declarations produce MyRegex).

Copilot

Pull request overview

This PR fixes issue #77409 where the SYSLIB1045 code fixer (which converts Regex constructor calls to GeneratedRegex) generates duplicate property names when applied to multiple partial class declarations via batch fixing. The root cause is that concurrent batch fixers all see the original compilation state before any fixes are applied, causing them to independently conclude that the same name (e.g., "MyRegex") is available.

The PR also includes two unrelated changes: a performance optimization using SetSearchValues for the regex interpreter, and a regression test for character class encoding validation.

Changes:

Adds CountPrecedingRegexCallSites helper to deterministically order all Regex call sites across partial declarations by file path and position, allowing each concurrent fixer to offset its name generation
Implements SetSearchValues optimization in the regex interpreter for vectorized character class matching
Adds validation for character class encoding before calling GetSetChars to prevent IndexOutOfRangeException on malformed input

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs	Adds CountPrecedingRegexCallSites helper and name offset logic to prevent duplicate names in batch fixing
src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs	Adds test validating unique name generation across partial class declarations
src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreterCode.cs	Adds SetSearchValues precomputation and character class encoding validation (unrelated optimization)
src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreter.cs	Uses SetSearchValues for vectorized Set opcode matching (unrelated optimization)
src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs	Adds regression test for Multi literal resembling character class encoding (unrelated)

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

...System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

...es/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreterCode.cs

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

Copilot

Pull request overview

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

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

...System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

...System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs

…artial class declarations When the BatchFixer applies multiple fixes concurrently, each fix sees the original compilation and independently picks the same first-available name. This causes CS0756 when two partial declarations of the same class both contain Regex calls that need fixing. The fix scans all partial declarations of the containing type for Regex call sites that would generate new property names, orders them deterministically (by file path, then position), and offsets the generated name by the current node's index in that list. Fixes dotnet#77409 Co-authored-by: Copilot <[email protected]>

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs

Extract fixable method names into shared FixableMethodNames set on the analyzer, referenced by both the analyzer and the fixer. Add test verifying Regex.Escape calls don't inflate the generated name offset. Co-authored-by: Copilot <[email protected]>

danmoseley · 2026-02-21T06:20:34Z

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexAnalyzer.cs

            // Creates a HashSet of all of the method Symbols containing the static methods to analyze.
            static HashSet<IMethodSymbol> GetMethodSymbolHash(INamedTypeSymbol regexTypeSymbol, HashSet<string> methodNames)
            {
-                // This warning is due to a false positive bug https://github.com/dotnet/roslyn-analyzers/issues/5804


noticed comment was dead, should have been removed with the pragma

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

...System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs

danmoseley · 2026-02-21T08:39:31Z

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danmoseley force-pushed the fix/77409-codefixer-duplicate-namesc branch from ec91456 to ca22fda Compare February 21, 2026 05:24

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