[OpenTelemetry] Fix NotSupportedException

[martincostello]

Fixes #7787

Changes

The internal limit on automata in .NET 8 is 1,000 but for .NET 9+ it's 10,000, which could cause NotSupportedException on .NET 8 when building the wildcard Regex for a large number of activity sources.

In usage with a lot of TracerProvider instances being created, non-backtracking could also cause OutOfMemoryException to be thrown, as it consumes ~35x more memory per Regex.

The fix is to stop using RegexOptions.NonBacktracking and use RegexOptions.Compiled for all TFMs. The match timeout should guard against the scenarios that prompted the original change.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[opentelemetry-pr-dashboard]

Pull request dashboard status

Merged · refreshed 2026-09-21 06:30 UTC

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[Copilot]

Copilot review overview

🟢 Approval recommended

The focused fix handles the reported exception with bounded fallback behavior and regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes wildcard regex construction failures on .NET 8.

Changes:

• Falls back to a timeout-bounded backtracking regex.
• Adds regression coverage and changelog documentation.

File	Description
src/​OpenTelemetry/​Internal/​WildcardHelper.cs	Adds safe regex fallback.
test/​OpenTelemetry.Tests/​Internal/​WildcardHelperTests.cs	Tests large pattern collections.
src/​OpenTelemetry/​CHANGELOG.md	Documents the fix.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.87%. Comparing base (7d1bd16) to head (1cb15a9).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7788      +/-   ##
==========================================
- Coverage   91.90%   91.87%   -0.04%     
==========================================
  Files         339      339              
  Lines       18543    18545       +2     
==========================================
- Hits        17042    17038       -4     
- Misses       1501     1507       +6     

Flag	Coverage Δ
unittests-Project-Experimental	91.94% <100.00%> (-0.07%)	⬇️
unittests-Project-Stable	91.91% <100.00%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/Internal/WildcardHelper.cs	100.00% <ø> (ø)
.../Metrics/Builder/MeterProviderBuilderExtensions.cs	98.60% <100.00%> (+0.02%)	⬆️

... and 3 files with indirect coverage changes

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation directly addresses the reported failures with appropriate timeout protection, regression tests, and changelog coverage.

Review effort: Balanced
Findings: None

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused implementation addresses the reported failure with appropriate timeout protection, regression coverage, and changelog documentation.

Review effort: Balanced
Findings: None