golang/go · error

evaluating condition

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.

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

• condition cannot be used with a suffix
• condition requires a suffix
• %s:%d: %w
• unknown condition prefix
• unknown condition prefix

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

Appendix: 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"))
	}

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