github/copilot-sdk · warning

failed to evaluate build constraints in

Error message

failed to evaluate build constraints in %q: %w

What it means

While scanning candidate .go files to detect the package name, detectPackageName calls buildContext.MatchFile to evaluate build constraints (build tags, GOOS/GOARCH fit). This error wraps any failure from that evaluation for a specific file, falling back to defaultPackageName.

Solutions

1. Open the file named in the error and fix its //go:build / // +build constraint syntax.
2. Remove or regenerate the offending file if it is generated or vestigial.
3. Run `go vet ./...` on the directory to surface malformed build constraints.
4. Ensure only one of //go:build and // +build is authoritative and they agree.

Example fix

// before (broken constraint in file.go)
// +build linux amd64
//go:build linux && amd64 &&

// after
//go:build linux && amd64
// +build linux,amd64

matches, err := buildContext.MatchFile(dir, name)
if err != nil {
    log.Printf("skipping %s: bad build constraints: %v", filepath.Join(dir, name), err)
    continue // or fix the file, depending on strictness
}

When it happens

Trigger: A .go file in the package directory has malformed build constraints (e.g. malformed //go:build lines) that go/build cannot parse for the target platform, causing buildContext.MatchFile(dir, name) to return an error.

Common situations: Hand-edited or conflicting //go:build and // +build lines; non-UTF8 or corrupt files; generated files with broken constraint syntax; cross-compiling to a platform where constraint evaluation hits an unsupported combination.

Related errors

• failed to read package directory
• CreateSessionFSProvider is required in session config when…
• SessionFS capabilities declare SQLite support but the…
• invalid platform
• failed to get SDK version

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/7c8370be929ea574. Report an issue: GitHub.

Appendix: source

Thrown at go/cmd/bundler/main.go:234

	if err != nil {
		return defaultPackageName, fmt.Errorf("failed to read package directory %q: %w", dir, err)
	}

	buildContext := build.Default
	buildContext.GOOS = goos
	buildContext.GOARCH = goarch

	packageName := ""
	for _, entry := range entries {
		name := entry.Name()
		if entry.IsDir() || !strings.HasSuffix(name, ".go") ||
			strings.HasPrefix(name, ".") || strings.HasPrefix(name, "_") ||
			strings.HasSuffix(name, "_test.go") || strings.HasPrefix(name, "zcopilot_") {
			continue
		}
		matches, err := buildContext.MatchFile(dir, name)
		if err != nil {
			return defaultPackageName, fmt.Errorf("failed to evaluate build constraints in %q: %w", filepath.Join(dir, name), err)
		}
		if !matches {
			continue
		}

		path := filepath.Join(dir, name)
		file, err := parser.ParseFile(token.NewFileSet(), path, nil, parser.PackageClauseOnly)
		if err != nil {
			return defaultPackageName, fmt.Errorf("failed to parse package clause in %q: %w", path, err)
		}

		if packageName == "" {
			packageName = file.Name.Name
			continue
		}
		if packageName != file.Name.Name {
			return defaultPackageName, fmt.Errorf("multiple packages %q and %q found in %q", packageName, file.Name.Name, dir)
		}

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