github/copilot-sdk · error

failed to read existing Go file

Error message

failed to read existing Go file: %w

What it means

checkEmbeddedVersion reads the previously generated Go file that records the embedded CLI version. If os.ReadFile fails for any reason other than the file not existing (IsNotExist returns early with nil), the error is wrapped with this message. It means an existing version file is present but unreadable.

Solutions

1. Check the wrapped underlying error for the exact cause (permission vs EISDIR vs I/O)
2. Fix file permissions on the generated Go file (chown/chmod) or run the bundler as the file's owner
3. If the path became a directory, remove it or update goFilePath generation
4. Delete the stale file so the next run regenerates it (the not-exist path is tolerated)

Example fix

// before
return fmt.Errorf("failed to read existing Go file: %w", err)
// after
return fmt.Errorf("failed to read existing Go file %s: %w", goFilePath, err) // include path to ease diagnosis

// check readability before bundler runs
if _, err := os.ReadFile(goFilePath); err != nil && !os.IsNotExist(err) {
	// fix permissions/path beforehand
}

// Go
if err := checkEmbeddedVersion(detected, goos, goarch, outDir); err != nil {
	if errors.Is(err, fs.ErrPermission) { /* chown/chmod and retry */ }
}

When it happens

Trigger: os.ReadFile on goFilePath fails with a permission error, the path is a directory, or an I/O error occurs — any non-ENOENT failure. The IsNotExist case is intentionally tolerated (nothing to check).

Common situations: File locked down by a previous build running as another user; path is now a directory due to layout change; stale build artifacts on a failing disk or read-only mounted output dir.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

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• SessionFS capabilities declare SQLite support but the…
• failed to read package directory
• failed to evaluate build constraints in
• failed to hash runtime assets

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/633fc372385db894. Report an issue: GitHub.

Appendix: source

Thrown at go/cmd/bundler/main.go:1296

	if err != nil {
		return fmt.Errorf("failed to add zstd dependency: %w\n%s", err, strings.TrimSpace(string(output)))
	}
	return nil
}

// checkEmbeddedVersion checks if an embedded CLI version exists and compares it with the detected version.
func checkEmbeddedVersion(detectedVersion, goos, goarch, outputDir string) error {
	// Look for the generated Go file for this platform
	goFileName := fmt.Sprintf("zcopilot_%s_%s.go", goos, goarch)
	goFilePath := filepath.Join(outputDir, goFileName)

	data, err := os.ReadFile(goFilePath)
	if err != nil {
		if os.IsNotExist(err) {
			// No existing embedded version, nothing to check
			return nil
		}
		return fmt.Errorf("failed to read existing Go file: %w", err)
	}

	// Extract version from the generated file
	// Looking for: Version: "x.y.z",
	re := regexp.MustCompile(`Version:\s*"([^"]+)"`)
	matches := re.FindSubmatch(data)
	if matches == nil {
		// Can't parse version, skip check
		return nil
	}

	embeddedVersion := string(matches[1])
	fmt.Printf("Found existing embedded version: %s\n", embeddedVersion)

	// Compare versions
	if embeddedVersion != detectedVersion {
		return fmt.Errorf("embedded version %s does not match detected version %s - update required", embeddedVersion, detectedVersion)
	}

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