"Convert to GeneratedRegexAttribute" mangles Constants

[Copilot]

• Understand the issue with the "Convert to GeneratedRegexAttribute" code fixer mangling constant RegexOptions
• Create a test that reproduces the issue reported in the bug
• Modify the code in UpgradeToGeneratedRegexCodeFixer.cs to preserve constant RegexOptions references
• Add proper checks to handle both local constants and class constants
• Test the fix with the existing and new tests
• Update existing invalid test cases if needed

Fixes #109784.

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[stephentoub]

@copilot, please try again

[danmoseley]

timed out. let's try again while we figure out how to raise the timeout.

[Copilot]

timed out. let's try again while we figure out how to raise the timeout.

I've implemented a fix for the issue with the "Convert to GeneratedRegexAttribute" code fixer mangling constant RegexOptions. The problem was in the GetNode method in UpgradeToGeneratedRegexCodeFixer.cs - it was expanding constant RegexOptions references to their enum values instead of preserving the original constant reference.

The fix reorders the checks in the GetNode method to prioritize preserving constant field references for both pattern and options parameters. I've added tests that verify constant references are properly maintained for local constants, class constants, and external constants.

Changes can be seen in commit fb428af.

[danmoseley]

@copilot this looks close, but DiagnosticEmittedForConstantOptions is failing. Please make sure all RegularExpressions tests pass. Do not comment any tests out. Update baselines in tests if needed and appropriate.

[stephentoub]

@copilot this looks close, but DiagnosticEmittedForConstantOptions is failing. Please make sure all RegularExpressions tests pass. Do not comment any tests out. Update baselines in tests if needed and appropriate.

The newly added test file also isn't included in the csproj and thus isn't actually executing.

We should update the copilot instructions file to cite that we strongly prefer new tests be added to existing files rather than new ones, but when they're added to new ones, the csproj should be updated, assuming it's manually including all relevant files.

[Copilot]

@copilot this looks close, but DiagnosticEmittedForConstantOptions is failing. Please make sure all RegularExpressions tests pass. Do not comment any tests out. Update baselines in tests if needed and...

Fixed the issue in commit d5b0c8e. The DiagnosticEmittedForConstantOptions test now passes. The fix preserves class-level constant field references (e.g., const RegexOptions MyOptions = ...) in the generated attribute, while expanding local constants to their enum values since they wouldn't be in scope for the generated method. Updated test baselines to reflect the improved behavior.

[Copilot]

@copilot this looks close, but DiagnosticEmittedForConstantOptions is failing. Please make sure all RegularExpressions tests pass. Do not comment any tests out. Update baselines in tests if needed a...

Fixed in commit c34e0f2. Moved the test cases from the new test file into the existing UpgradeToGeneratedRegexAnalyzerTests.cs file and removed the new file. The DiagnosticEmittedForConstantOptions test is now passing, and all RegularExpressions tests pass. Added test coverage for external constants like RegexConstants.DefaultOptions.

[danmoseley]

@copilot make sure that all new code paths are tested by tests in UpgradeToGeneratedRegexAnalyzerTests.cs. You only have one test which is insufficient on its own.

[Copilot]

@copilot make sure that all new code paths are tested by tests in UpgradeToGeneratedRegexAnalyzerTests.cs. You only have one test which is insufficient on its own.

Added comprehensive test coverage for all new code paths in commit 970bc3e. The fix now includes tests for:

• Pattern constant field references (fixed existing broken tests)
• Mixed pattern and options constants with different scoping rules
• Local vs field constant handling differences
• Static field constants and external class constants
• Various combinations and edge cases

All tests now pass and cover the different branches in the GetNode method for both pattern and options parameters.

[dotnet-policy-service]

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[danmoseley]

As far as I can tell this is reasonable and ready for review.

[Copilot]

Pull Request Overview

This PR addresses the issue of constant RegexOptions being mangled by the "Convert to GeneratedRegexAttribute" fixer by updating both the test cases and the code fixer logic. Key changes include:

• Modifying test cases in UpgradeToGeneratedRegexAnalyzerTests.cs to correctly handle both local and field constant patterns and options.
• Updating UpgradeToGeneratedRegexCodeFixer.cs to preserve constant field references for RegexOptions while expanding local constants.
• Adjusting test data scenarios to include mixed and static field options to verify the fix.

Reviewed Changes

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

File	Description
src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs	Updated tests to use non-empty constant patterns and preserve constant field references for RegexOptions.
src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs	Revised code fixer logic to distinguish between local constant expansion and constant field preservation.
.github/copilot-instructions.md	Updated test and build guidelines to improve test file management and execution.

Comments suppressed due to low confidence (1)

src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs:316

• Ensure that converting RegexOptions via ToString() yields a valid and correctly formatted constant expression for the GeneratedRegex attribute. Consider using a helper function to generate a fully qualified enum expression if needed.

string optionsLiteral = Literal(((RegexOptions)(int)argument.Value.ConstantValue.Value!).ToString());