What causes "%s/%s is missing module path at revision %s" in golang/go?

Open the offending go.mod in the source repo and add a proper `module ` directive.

%s/%s is missing module path at revision %s

Error message

%s/%s is missing module path at revision %s

What it means

findDir (coderepo.go:874-877). The major-subdir go.mod (file2) was read successfully (err2 == nil) but modfile.ModulePath returned an empty string — the file has no `module` directive. Without a declared module path the file cannot be validated for the expected major version.

Source

Thrown at src/cmd/go/internal/modfetch/coderepo.go:876

		// a replace directive.
		dir2 := path.Join(r.codeDir, r.pathMajor[1:])
		file2 = path.Join(dir2, "go.mod")
		gomod2, err2 := r.code.ReadFile(ctx, rev, file2, codehost.MaxGoMod)
		if err2 != nil && !os.IsNotExist(err2) {
			return "", "", nil, fmt.Errorf("reading %s/%s at revision %s: %v", r.codeRoot, file2, rev, err2)
		}
		mpath2 := modfile.ModulePath(gomod2)
		found2 := err2 == nil && isMajor(mpath2, r.pathMajor)

		if found1 && found2 {
			return "", "", nil, fmt.Errorf("%s/%s and ...%s/go.mod both have ...%s module paths at revision %s", r.pathPrefix, file1, r.pathMajor, r.pathMajor, rev)
		}
		if found2 {
			return rev, dir2, gomod2, nil
		}
		if err2 == nil {
			if mpath2 == "" {
				return "", "", nil, fmt.Errorf("%s/%s is missing module path at revision %s", r.codeRoot, file2, rev)
			}
			return "", "", nil, fmt.Errorf("%s/%s has non-...%s module path %q at revision %s", r.codeRoot, file2, r.pathMajor, mpath2, rev)
		}
	}

	// Not v2/go.mod, so it's either go.mod or nothing. Which is it?
	if found1 {
		// Explicit go.mod with matching major version ok.
		return rev, r.codeDir, gomod1, nil
	}
	if err1 == nil {
		// Explicit go.mod with non-matching major version disallowed.
		suffix := ""
		if file2 != "" {
			suffix = fmt.Sprintf(" (and ...%s/go.mod does not exist)", r.pathMajor)
		}
		if mpath1 == "" {
			return "", "", nil, fmt.Errorf("%s is missing module path%s at revision %s", file1, suffix, rev)

View on GitHub (pinned to b6b368adc5)

Solutions

Open the offending go.mod in the source repo and add a proper `module <path>` directive.
Remove the file if the major-subdir layout is not intended (let the root go.mod win).
Re-tag and update the dependency version.

Example fix

// before: v2/go.mod
//   go 1.21

// after: v2/go.mod
//   module example.com/m/v2
//
//   go 1.21

Defensive patterns

Strategy: validation

Validate before calling

// Lint: every committed go.mod must have a module directive.
// bash:
//   find . -name go.mod -print0 | xargs -0 -I{} sh -c 'grep -qE "^module " "{}" || echo "missing module: {}"'
// Go:
//   path, err := modfile.Parse(...) // ensure Module.Path != ""

Prevention

Always include a `module` directive when creating go.mod.
Add a pre-commit hook that rejects go.mod files without a module path.
Run `go mod tidy` after editing go.mod to catch structural problems.

When it happens

Trigger: A /v2/go.mod exists in the repo but is empty, malformed at the top, or simply lacks a `module` line. modfile.ModulePath returns "" for files missing the directive.

Common situations: Placeholder go.mod committed by mistake; partially generated go.mod; the file was truncated during a mirror sync; go.mod written as a Go directive without the keyword.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/982350262a50e9c2. Report an issue: GitHub.