What causes "no scheme" in dagger/dagger?

Check the import path against the Prefix values in the page's go-import tags and use the advertised prefix

no scheme

Error message

no scheme

What it means

errNoMatch ('no import match') is the sentinel error returned by matchGoImport when none of the parsed go-import meta tags' prefixes is a whole-path-component prefix of the requested import path. In RepoRootForImportDynamic it is translated into 'parse %s: no go-import meta tags' rather than propagated as-is; in matchGoImport's second call site it surfaces as the bare sentinel.

Source

Thrown at engine/vcs/vcs.go:532

		// e.g. Bitbucket, GitLab
		Repo: strings.TrimSuffix(metaImport.RepoRoot, ".git"),
		Root: metaImport.Prefix,
	}
	if rr.VCS == nil {
		return nil, fmt.Errorf("%s: unknown vcs %q", urlStr, metaImport.VCS)
	}
	return rr, nil
}

// validateRepoRoot returns an error if repoRoot does not seem to be
// a valid URL with scheme.
func validateRepoRoot(repoRoot string) error {
	url, err := url.Parse(repoRoot)
	if err != nil {
		return err
	}
	if url.Scheme == "" {
		return errors.New("no scheme")
	}
	return nil
}

// metaImport represents the parsed <meta name="go-import"
// content="prefix vcs reporoot" /> tags from HTML files.
type metaImport struct {
	Prefix, VCS, RepoRoot string
}

// errNoMatch is returned from matchGoImport when there's no applicable match.
var errNoMatch = errors.New("no import match")

// pathPrefix reports whether sub is a prefix of s,
// only considering entire path components.
func pathPrefix(s, sub string) bool {
	// strings.HasPrefix is necessary but not sufficient.
	if !strings.HasPrefix(s, sub) {

View on GitHub (pinned to 82ba2681db)

Solutions

Check the import path against the Prefix values in the page's go-import tags and use the advertised prefix
Update the meta tag to cover the full module path, e.g. content="uni.edu/bobby/proj vcs repo"
Remember prefix matching is per path component: 'uni.edu/bob' does not match 'uni.edu/bobby/proj'
If the error message is 'parse <url>: no go-import meta tags', it means errNoMatch occurred after tags were parsed — compare paths carefully

Example fix

<!-- before: prefix doesn't cover the import -->
<meta name="go-import" content="uni.edu/bob git https://github.com/bob/proj">
<!-- importing uni.edu/bobby/proj fails -->
<!-- after -->
<meta name="go-import" content="uni.edu/bobby/proj git https://github.com/bob/proj">

Defensive patterns

Strategy: try-catch

Validate before calling

func tagMatchesPath(tag, importPath string) bool {
    prefix := strings.Fields(tag)[0]
    rem := strings.TrimPrefix(importPath, prefix)
    return strings.HasPrefix(importPath, prefix) && (rem == "" || strings.HasPrefix(rem, "/"))
}

Try / catch

rr, err := RepoRootForImportDynamic(path, false)
if err != nil && strings.Contains(err.Error(), "no go-import meta tags") {
    return fmt.Errorf("no meta tag prefix covers %q; verify module name matches the tag prefix", path)
}

Prevention

Import exactly the module path declared by the meta tag prefix
Remember prefix matching is component-wise: /bob never matches /bobby
Test one representative import per module prefix in CI
Keep a single authoritative prefix list for your vanity domain

When it happens

Trigger: Calling RepoRootForImportDynamic on an import path whose host page contains go-import meta tags but none whose Prefix matches the path at a path-component boundary, e.g. page advertises prefix 'uni.edu/bob' while importing 'uni.edu/bobby/proj'. Also returned directly from matchGoImport in tests.

Common situations: Typo in the import path (wrong module name); meta tag prefix doesn't cover the imported subpackage; trailing-segment mismatches after removing '..' components; importing a path the vanity host deliberately doesn't serve.

Related errors

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/adff4b0f43bf5ffc. Report an issue: GitHub.