[dashpole]

Part of #9446

Summary

In Go, errors.Join is commonly used to accumulate optional errors across operations—for example, uploadErr = errors.Join(uploadErr, err) where uploadErr starts as nil. When only one non-nil error is passed (e.g., errors.Join(nil, err)), errors.Join still wraps that single error in an unexported *errors.joinError implementing Unwrap() []error (not Unwrap() error).

When no error in the chain implements ErrorType() string, semconv.ErrorType and sdk/log fall back to reflection after unwrapping *fmt.wrapError (#8133). Because errors.Unwrap returns nil for Unwrap() []error, single-error errors.Join wrappers were not unwrapped and caused instrumentation and SDK self-observability metrics to report the opaque error.type="*errors.joinError" instead of the underlying error's concrete type.

Approach

• Extend the reflection-fallback unwrapping helper in internal/tools/semconvkit/templates/error_type.go.tmpl, semconv/v1.44.0/error_type.go, and sdk/log/logger.go to iteratively unwrap both *fmt.wrapError (fmt.Errorf with single %w) and single-error *errors.joinError (errors.Join when len(u.Unwrap()) == 1).
• Preserve existing behavior when errors.Join wraps multiple non-nil errors (len > 1 continues to report *errors.joinError) and when custom user-defined error types implement Unwrap() []error (custom wrapper types continue to report their top-level concrete type, matching #8133 / #7975).

Alternatives Considered

• Avoiding errors.Join at individual call sites inside opentelemetry-go: Only fixes internal call sites and leaves external instrumentation and callers using errors.Join(nil, err) reporting *errors.joinError. Handling single-error errors.Join alongside fmt.Errorf in semconv and sdk/log fixes this consistently across the ecosystem.
• Unwrapping arbitrary Unwrap() []error implementations with len == 1: Rejected for the same reason #8133 / #7975 restricted single-error unwrapping to fmt.Errorf: user-defined domain error types implementing Unwrap() []error carry meaningful top-level type identity that should not be stripped.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Merged · refreshed 2026-11-09 20:47 UTC

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.8%. Comparing base (63c5f44) to head (d543e05).

Files with missing lines	Patch %	Lines
semconv/v1.44.0/error_type.go	0.0%	13 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #9466     +/-   ##
=======================================
- Coverage   89.8%   89.8%   -0.1%     
=======================================
  Files        357     357             
  Lines      23965   23977     +12     
=======================================
+ Hits       21535   21541      +6     
- Misses      2430    2436      +6     

Files with missing lines	Coverage Δ
sdk/log/logger.go	100.0% <100.0%> (ø)
semconv/v1.44.0/error_type.go	0.0% <0.0%> (ø)

... and 3 files with indirect coverage changes

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[Copilot]

🟢 Approval recommended

There are no active review issues for the changes that derive meaningful error types through single-error join wrappers.

No open issues 🎉

_{Review effort: Balanced}

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