golang/go · error

can't decode input %s: %v

Error message

can't decode input %s: %v

What it means

Thrown by `go tool export` (src/cmd/export/main.go) readConfig when the .cfg config file (produced by `go list -export`) is read successfully but cannot be JSON-unmarshalled into the config struct (ImportPath, Compiler, GoVersion, GoFiles, ImportMap, PackageFile, Output). The error wraps the filename and the json error. The export tool is internal, driven only by `go list -export`.

Source

Thrown at src/cmd/export/main.go:122

	f, err := os.Create(cfg.Output)
	if err != nil {
		return err
	}
	if err := gcexportdata.Write(f, fset, pkg); err != nil {
		f.Close() // ignore error
		return err
	}
	return f.Close()
}

func readConfig(filename string) (*config, error) {
	data, err := os.ReadFile(filename)
	if err != nil {
		return nil, err
	}
	cfg := new(config)
	if err := json.Unmarshal(data, cfg); err != nil {
		return nil, fmt.Errorf("can't decode input %s: %v", filename, err)
	}
	if len(cfg.GoFiles) == 0 {
		return nil, fmt.Errorf("no files in package %s", cfg.ImportPath)
	}
	return cfg, nil
}

func makeTypesImporter(cfg *config, fset *token.FileSet) types.Importer {
	imports := make(map[string]*types.Package)
	imports["unsafe"] = types.Unsafe
	return importerFunc(func(importPath string) (*types.Package, error) {
		pkgPath, ok := cfg.ImportMap[importPath]
		if !ok {
			return nil, fmt.Errorf("can't resolve import %s", importPath)
		}
		// Check for cache hit.
		if pkg, ok := imports[pkgPath]; ok && pkg.Complete() {
			return pkg, nil

View on GitHub (pinned to b6b368adc5)

Solutions

1. Regenerate the .cfg via `go list -export` rather than editing it
2. Validate the .cfg parses as JSON and has the expected top-level fields (GoFiles array, ImportMap map, etc.)
3. Ensure the go and export binaries are from the same GOROOT/release
4. Do not invoke `go tool export` directly — it is undocumented and exists for `go list -export`

Example fix

# before (hand-edited / truncated cfg)
go tool export broken.cfg
# after (regenerate)
go list -export -json ./...  # produces valid .cfg
go build ./...

# Validate the .cfg before relying on export
python3 -c "import json; c=json.load(open('unit.cfg')); assert c.get('GoFiles'), 'GoFiles missing'" || echo "bad cfg"

When it happens

Trigger: `go list -export` (or a direct `go tool export unit.cfg`) where unit.cfg contains invalid JSON or fields whose types do not match the config struct. Reachable only via the export toolchain subcommand.

Common situations: Truncated .cfg from a killed build. Version skew between go and go-tool-export. A hand-crafted or edited .cfg. Disk write corruption. Mixing gccgo/gc config formats.

Related errors

• no files in package %s
• decoding go list json: %v
• can't resolve import %s
• can't resolve export %s
• cannot run go list: %v %s

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/a53413d7d0d31624. Report an issue: GitHub.