Use invariant culture when formatting capture transfer in regex source generator

[stephentoub]

A balancing group can result in TransferCapture being emitted with a negative "capnum". If the compiler is running under a culture that uses something other than '-' as the negative sign, the resulting generated code will fail to compile.

Fixes #113077

PR Overview

This PR fixes a bug where a balancing group could result in the generated code emitting a negative capture number using the wrong culture-specific negative sign.

• Introduces a custom culture (s_cultureWithMinusNegativeSign) for testing that uses a non-standard negative sign.
• Updates code in the emitter to format the capnum using CultureInfo.InvariantCulture.

Reviewed Changes

File	Description
src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs	Added a custom culture to simulate an alternate negative sign and updated culture handling in the generator run block.
src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs	Modified the TransferCapture call to format capnum with CultureInfo.InvariantCulture.

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

Comments suppressed due to low confidence (2)

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs:2576

• The change correctly formats capnum with CultureInfo.InvariantCulture; consider reviewing if other numeric parameters (e.g., uncapnum) should also be formatted invariantly for consistency.

writer.WriteLine($"base.TransferCapture({capnum.ToString(CultureInfo.InvariantCulture)}, {uncapnum}, {startingPos}, pos);");

src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs:137

• [nitpick] Consider using an explicit culture identifier (e.g., "en-US") when initializing s_cultureWithMinusNegativeSign to clarify its intended purpose, rather than an empty string.

private static readonly CultureInfo s_cultureWithMinusNegativeSign = new CultureInfo("")

Tip: Copilot code review supports C#, Go, Java, JavaScript, Markdown, Python, Ruby and TypeScript, with more languages coming soon. Learn more

[stephentoub]

/backport to release/9.0-staging

[github-actions]

Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/13657696434

[stephentoub]

/backport to release/8.0-staging

[github-actions]

Started backporting to release/8.0-staging: https://github.com/dotnet/runtime/actions/runs/13657711369

[github-actions]

@stephentoub backporting to "release/9.0-staging" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Use invariant culture when formatting transfer capture in regex source generator
Using index info to reconstruct a base tree...
M	src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
Falling back to patching base and 3-way merge...
Auto-merging src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
CONFLICT (content): Merge conflict in src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 Use invariant culture when formatting transfer capture in regex source generator
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

[github-actions]

@stephentoub backporting to "release/8.0-staging" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Use invariant culture when formatting transfer capture in regex source generator
Using index info to reconstruct a base tree...
M	src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
M	src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs
Falling back to patching base and 3-way merge...
Auto-merging src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs
Auto-merging src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
CONFLICT (content): Merge conflict in src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 Use invariant culture when formatting transfer capture in regex source generator
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!