golang/go · error

evaluating condition %q: %w

Error message

evaluating condition %q: %w

What it means

Engine.conditionsActive wraps any error returned by a Cond's Eval method with the condition tag (engine.go:537-539). The inner %w error is typically one of the 'unrecognized GOOS/GOARCH/compiler/GOEXPERIMENT' errors, indicating the suffix value is syntactically valid (known prefix) but the value itself is invalid.

Source

Thrown at src/cmd/internal/script/engine.go:538

			if impl == nil {
				return false, fmt.Errorf("unknown condition prefix %q; known: %v", prefix, slices.Collect(maps.Keys(e.Conds)))
			}
			if !impl.Usage().Prefix {
				return false, fmt.Errorf("condition %q cannot be used with a suffix", prefix)
			}
		} else {
			impl = e.Conds[cond.tag]
			if impl == nil {
				return false, fmt.Errorf("unknown condition %q", cond.tag)
			}
			if impl.Usage().Prefix {
				return false, fmt.Errorf("condition %q requires a suffix", cond.tag)
			}
		}
		active, err := impl.Eval(s, suffix)

		if err != nil {
			return false, fmt.Errorf("evaluating condition %q: %w", cond.tag, err)
		}
		if active != cond.want {
			return false, nil
		}
	}

	return true, nil
}

func (e *Engine) runCommand(s *State, cmd *command, impl Cmd) error {
	if impl == nil {
		return cmdError(cmd, errors.New("unknown command"))
	}

	async := impl.Usage().Async
	if cmd.background && !async {
		return cmdError(cmd, errors.New("command cannot be run in background"))
	}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Read the wrapped inner error to identify which value is unrecognized.
2. Fix the suffix to a valid value for that condition (see KnownOS/KnownArch/buildcfg experiment list).
3. If the value was removed in a newer Go version, gate the line behind a version check or remove it.

Example fix

// before
[GOOS:macos] exec go build   // -> evaluating condition "GOOS:macos": unrecognized GOOS "macos"
// after
[GOOS:darwin] exec go build

// errors.Is / errors.As on the wrapped chain to distinguish cause.
if errors.Is(err, something) { ... }
// The inner error after 'evaluating condition %q:' reveals the rejected value.

When it happens

Trigger: Using [GOOS:linnux] — the prefix GOOS is known, so execution reaches the eval closure, which then rejects the unknown value 'linnux' and that error is wrapped here. Same for [compiler:gcc], [GOEXPERIMENT:bogus].

Common situations: Correct condition name but misspelled suffix value; experiment renamed across Go versions; using a value valid in one context but not the current build.

Related errors

• unrecognized GOOS %q
• unrecognized GOARCH %q
• unrecognized compiler %q
• %s:%d: %w
• unknown condition prefix %q; known: %v

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/8f241b934269d4a3. Report an issue: GitHub.