Fix SYSLIB1045 code fixer generating duplicate MyRegex names across partial class declarations

[danmoseley]

Fixes #77409

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)

[Copilot]

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[Copilot]

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

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[Copilot]

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

[danmoseley]

ready for review

[danmoseley]

Dan to try more manual validation locally.

[danmoseley]

Added edge case tests and found/fixed a bug in CountPrecedingRegexCallSites:

Bug fix: The nested-type exclusion check descendant.Ancestors().Any(a => a is TypeDeclarationSyntax && a != declSyntax) incorrectly skipped calls when the type being fixed is itself nested inside another type. For example, if Inner is nested inside Outer, calls inside Inner's partial declarations would be skipped because Outer is an ancestor TypeDeclarationSyntax != declSyntax. This caused both calls in Inner to get the same name MyRegex. Fixed by using .TakeWhile(a => a != declSyntax) to only check ancestors within the declaring syntax node.

Tests added:

• NestedTypeCallsDoNotAffectOuterTypeNaming — inner class Regex calls excluded from outer type naming
• NonConstantPatternDoesNotAffectNaming — new Regex(variable) not counted
• PartialStructGeneratesUniqueNames — partial structs work, not just classes
• MixedConstructorAndStaticMethodCallsAcrossPartials — new Regex() + Regex.IsMatch() get unique names
• NestedPartialTypeDoesNotInterfereWithOuterPartial — nested partial type has independent naming (exercises the bug fix)

[danmoseley]

@stephentoub I can't remember what I volunteered to try out locally. I remember looking more at nested types, added various tests above and these found one bug. Anything else here?

[Copilot]

Pull request overview

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

[stephentoub]

I can't remember what I volunteered to try out locally.

Making sure that lots of regexes that would all conflict in names, spread out in various ways throughout the project, all auto-fix automatically / correctly in a batch.

[danmoseley]

Addressed review feedback in 0fa6a45:

• Tree-index tiebreaker: Sort key is now (FilePath, TreeIndex, Position) instead of (FilePath, Position), preventing indeterminate ordering when SyntaxTree.FilePath is null/empty (e.g., in-memory documents).
• SemanticModel cache: Avoids redundant GetSemanticModel calls when multiple partial declarations share the same SyntaxTree.
• Dismissed the ImmutableHashSet suggestion — for 7 strings in an internal static readonly field that's never mutated, ImmutableHashSet is strictly slower (O(log n) tree lookups vs O(1) hash) with no practical safety benefit.

[danmoseley]

Did an integration test with a test project containing 28 fixable Regex calls spread across 12 files and 7 types (partial classes, partial structs, nested types, static methods, mixed fixable/non-fixable). Ran dotnet format analyzers --diagnostics SYSLIB1045 using the locally-built analyzer and verified all calls get unique names, unfixable calls are correctly skipped, and the result compiles and runs (diff).

Initially noticed a missing blank line between generated properties -- fixed that by adding ElasticCarriageReturnLineFeed leading trivia before AddMembers. Properties may appear in a different order than their corresponding call sites -- based on inspection of Roslyn's BatchFixAllProvider.cs, this appears to be its merge behavior rather than something the fixer controls.

[danmoseley]

Need to check blank lines/ordering aren't the fixer.

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[danmoseley]

Feedback addressed.