golang/go · error

import %q: import of unknown directory

Error message

import %q: import of unknown directory

What it means

Returned by IndexPackage.Import when p.Dir evaluates to an empty string. p.Dir is computed as filepath.Join(rp.modroot, rp.dir); an empty result implies both rp.modroot and rp.dir were empty, i.e. the IndexPackage was constructed without a usable module-root or relative-dir field. This is an internal-consistency failure rather than a user mistake.

Source

Thrown at src/cmd/go/internal/modindex/read.go:401

	defer unprotect(protect(), &err)

	ctxt := (*Context)(&bctxt)

	p = &build.Package{}

	p.ImportPath = "."
	p.Dir = filepath.Join(rp.modroot, rp.dir)

	var pkgerr error
	switch ctxt.Compiler {
	case "gccgo", "gc":
	default:
		// Save error for end of function.
		pkgerr = fmt.Errorf("import %q: unknown compiler %q", p.Dir, ctxt.Compiler)
	}

	if p.Dir == "" {
		return p, fmt.Errorf("import %q: import of unknown directory", p.Dir)
	}

	// goroot and gopath
	inTestdata := func(sub string) bool {
		sub = filepath.ToSlash(sub)
		return strings.Contains(sub, "/testdata/") || strings.HasSuffix(sub, "/testdata") || str.HasPathPrefix(sub, "testdata")
	}
	var pkga string
	if !inTestdata(rp.dir) {
		// In build.go, p.Root should only be set in the non-local-import case, or in
		// GOROOT or GOPATH. Since module mode only calls Import with path set to "."
		// and the module index doesn't apply outside modules, the GOROOT case is
		// the only case where p.Root needs to be set.
		if ctxt.GOROOT != "" && str.HasFilePathPrefix(p.Dir, cfg.GOROOTsrc) && p.Dir != cfg.GOROOTsrc {
			p.Root = ctxt.GOROOT
			p.Goroot = true
			modprefix := str.TrimFilePathPrefix(rp.modroot, cfg.GOROOTsrc)
			p.ImportPath = rp.dir

View on GitHub (pinned to b6b368adc5)

Solutions

1. Obtain IndexPackage instances only through (*Module).Package(path), which sets modroot and dir from the index.
2. If writing tests, populate rp.modroot and rp.dir explicitly.
3. Clear and rebuild the cache (`go clean -modcache`) if the index appears malformed.

// Ensure IndexPackage came from a populated Module.Package call.
func validIndexPackage(rp *modindex.IndexPackage) bool {
    // rp.Dir() returns the joined path; if empty, the struct is unusable.
    return rp.Dir() != ""
}

When it happens

Trigger: Importing an IndexPackage whose modroot/dir fields were never populated (e.g. a zero-value IndexPackage, or a synthetic test fixture). The check fires immediately after the compiler switch.

Common situations: Tooling that constructs IndexPackage literals without going through Module.Package; memory corruption of the index structures; tests that forget to populate dir fields.

Related errors

• import %q: unknown compiler %q
• invalid ASN.1 from SignASN1
• marshal error %v
• no clauses
• clause %q: expected colon

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/21cf134765ce5ae6. Report an issue: GitHub.