golang/go · error

unknown version control system %q

Error message

unknown version control system %q

What it means

When resolving a vanity import path, the go tool reads the `<meta name="go-import">` tag which specifies a VCS type (git, hg, svn, bzr, fossil). vcsByCmd looks up the named VCS in the known list; if the name is not recognized (typo or unsupported system like 'perforce'), the lookup returns nil and this error fires.

Source

Thrown at src/cmd/go/internal/vcs/vcs.go:871

		for i, name := range srv.regexp.SubexpNames() {
			if name != "" && match[name] == "" {
				match[name] = m[i]
			}
		}
		if srv.vcs != "" {
			match["vcs"] = expand(match, srv.vcs)
		}
		if srv.repo != "" {
			match["repo"] = expand(match, srv.repo)
		}
		if srv.check != nil {
			if err := srv.check(match); err != nil {
				return nil, err
			}
		}
		vcs := vcsByCmd(match["vcs"])
		if vcs == nil {
			return nil, fmt.Errorf("unknown version control system %q", match["vcs"])
		}
		if err := checkGOVCS(vcs, match["root"]); err != nil {
			return nil, err
		}
		var repoURL string
		if !srv.schemelessRepo {
			repoURL = match["repo"]
		} else {
			repo := match["repo"]
			var ok bool
			repoURL, ok = interceptVCSTest(repo, vcs, security)
			if !ok {
				scheme, err := func() (string, error) {
					for _, s := range vcs.Scheme {
						if security == web.SecureOnly && !vcs.isSecureScheme(s) {
							continue
						}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Check the discovery page: `curl -sL https://<import-path> | grep go-import`
2. If you control the vanity page, fix the VCS name in the meta tag to one of: git, hg, svn, bzr, fossil
3. Use a replace directive to point directly at the repository URL
4. Report the issue to the vanity path maintainer

Example fix

<!-- before: typo in VCS name -->
<meta name="go-import" content="example.com/pkg get https://github.com/me/pkg">

<!-- after: correct VCS name -->
<meta name="go-import" content="example.com/pkg git https://github.com/me/pkg">

# Pre-check the go-import meta tag for VCS validity
SUPPORTED_VCS='git hg svn bzr fossil'
META=$(curl -sL "https://$IMPORT_PATH?go-get=1" | grep -oP 'go-import" content="[^"]+"' | head -1)
META_VCS=$(echo "$META" | awk '{print $3}' | tr -d '"')
for v in $SUPPORTED_VCS; do
  [ "$META_VCS" = "$v" ] && echo "VCS OK: $v" && exit 0
done
echo "WARNING: unsupported VCS in meta tag: $META_VCS"

# Detect unknown VCS error and suggest using a replace directive
ERR=$(go get $IMPORT_PATH 2>&1)
if echo "$ERR" | grep -q 'unknown version control system'; then
  echo 'The vanity path declares an unsupported VCS.'
  echo 'Use a replace directive in go.mod to point directly at the repository.'
fi

When it happens

Trigger: A repository's go-import meta tag specifies a VCS name that isn't in the supported set: `<meta name="go-import" content="example.com/pkg perforce https://...">`, or a typo like 'get' instead of 'git'.

Common situations: Misconfigured vanity import page with a typo in the VCS field; a hosting service serving an incorrect go-import meta tag; a repository using an unsupported VCS.

Related errors

• can't decode XML document using charset %q
• %q not allowed in import path
• no %sprotocol found for repository
• invalid version control suffix in %s path
• ReadZip: encoded file exceeds allowed size

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/a6e891c28fb7702f. Report an issue: GitHub.