What causes "failed to convert version %q : %v" in hashicorp/nomad?

Correct the offending version string to valid semver (optional v prefix, numeric components)

failed to convert version %q : %v

Error message

failed to convert version %q : %v

What it means

convertVersions maps a []string of version strings to []*version.Version (sorted highest first) using hashicorp/go-version. It fails fast on the first string version.NewVersion cannot parse, wrapping the underlying parse error.

Source

Thrown at helper/pluginutils/loader/init.go:210

	for _, sv := range supportedVersions {
		for _, pv := range pluginVersions {
			if sv.Equal(pv) {
				return pv.Original(), nil
			}
		}
	}

	return "", nil
}

// convertVersions takes a list of string versions and returns a sorted list of
// versions from highest to lowest.
func convertVersions(in []string) ([]*version.Version, error) {
	converted := make([]*version.Version, len(in))
	for i, v := range in {
		vv, err := version.NewVersion(v)
		if err != nil {
			return nil, fmt.Errorf("failed to convert version %q : %v", v, err)
		}

		converted[i] = vv
	}

	sort.Slice(converted, func(i, j int) bool {
		return converted[i].GreaterThan(converted[j])
	})

	return converted, nil
}

// scan scans the plugin directory and retrieves potentially eligible binaries
func (l *PluginLoader) scan() ([]os.FileInfo, error) {
	if l.pluginDir == "" {
		return nil, nil
	}

View on GitHub (pinned to 482b49bf1a)

Solutions

Correct the offending version string to valid semver (optional v prefix, numeric components)
Inspect the wrapped %v to identify the exact string that failed
Add a unit test that runs convertVersions (or version.NewVersion) over the declared version list

Example fix

// before
convertVersions([]string{"v1.", "v2"})
// after
convertVersions([]string{"v1.0.0", "v2.0.0"})

Defensive patterns

Strategy: validation

Validate before calling

vv, err := version.NewVersion(candidate)
if err != nil {
    return fmt.Errorf("version %q rejected: %w", candidate, err)
}

Try / catch

if err := loader.Init(...); err != nil {
    if strings.Contains(err.Error(), "failed to convert version") {
        // scan all version strings with version.NewVersion to locate the bad one
    }
}

Prevention

Lint hardcoded version strings with a regex like ^v?\d+\.\d+\.\d+$
Unit-test convertVersions on every declared version list
Avoid building version strings via string concatenation of config values

When it happens

Trigger: Any of selectApiVersion, NewPluginLoader, or the internal anonymous helper passes a version string that go-version rejects (empty string, non-numeric, bad prerelease syntax).

Common situations: Hardcoded API version lists containing typos; environment/config-driven version strings interpolated incorrectly; using names like "v1" is fine but "v 1" or "1.0.0.0" is not.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/e4d99c07a83bacaa. Report an issue: GitHub.