Run Format

Source file src/go/format/format.go

Documentation: go/format

  // Copyright 2012 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  // Package format implements standard formatting of Go source.
  // Note that formatting of Go source code changes over time, so tools relying on
  // consistent formatting should execute a specific version of the gofmt binary
  // instead of using this package. That way, the formatting will be stable, and
  // the tools won't need to be recompiled each time gofmt changes.
  // For example, pre-submit checks that use this package directly would behave
  // differently depending on what Go version each developer uses, causing the
  // check to be inherently fragile.
  package format
  import (
  var config = printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
  const parserMode = parser.ParseComments
  // Node formats node in canonical gofmt style and writes the result to dst.
  // The node type must be *ast.File, *printer.CommentedNode, []ast.Decl,
  // []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec,
  // or ast.Stmt. Node does not modify node. Imports are not sorted for
  // nodes representing partial source files (for instance, if the node is
  // not an *ast.File or a *printer.CommentedNode not wrapping an *ast.File).
  // The function may return early (before the entire result is written)
  // and return a formatting error, for instance due to an incorrect AST.
  func Node(dst io.Writer, fset *token.FileSet, node interface{}) error {
  	// Determine if we have a complete source file (file != nil).
  	var file *ast.File
  	var cnode *printer.CommentedNode
  	switch n := node.(type) {
  	case *ast.File:
  		file = n
  	case *printer.CommentedNode:
  		if f, ok := n.Node.(*ast.File); ok {
  			file = f
  			cnode = n
  	// Sort imports if necessary.
  	if file != nil && hasUnsortedImports(file) {
  		// Make a copy of the AST because ast.SortImports is destructive.
  		// TODO(gri) Do this more efficiently.
  		var buf bytes.Buffer
  		err := config.Fprint(&buf, fset, file)
  		if err != nil {
  			return err
  		file, err = parser.ParseFile(fset, "", buf.Bytes(), parserMode)
  		if err != nil {
  			// We should never get here. If we do, provide good diagnostic.
  			return fmt.Errorf("format.Node internal error (%s)", err)
  		ast.SortImports(fset, file)
  		// Use new file with sorted imports.
  		node = file
  		if cnode != nil {
  			node = &printer.CommentedNode{Node: file, Comments: cnode.Comments}
  	return config.Fprint(dst, fset, node)
  // Source formats src in canonical gofmt style and returns the result
  // or an (I/O or syntax) error. src is expected to be a syntactically
  // correct Go source file, or a list of Go declarations or statements.
  // If src is a partial source file, the leading and trailing space of src
  // is applied to the result (such that it has the same leading and trailing
  // space as src), and the result is indented by the same amount as the first
  // line of src containing code. Imports are not sorted for partial source files.
  func Source(src []byte) ([]byte, error) {
  	fset := token.NewFileSet()
  	file, sourceAdj, indentAdj, err := parse(fset, "", src, true)
  	if err != nil {
  		return nil, err
  	if sourceAdj == nil {
  		// Complete source file.
  		// TODO(gri) consider doing this always.
  		ast.SortImports(fset, file)
  	return format(fset, file, sourceAdj, indentAdj, src, config)
  func hasUnsortedImports(file *ast.File) bool {
  	for _, d := range file.Decls {
  		d, ok := d.(*ast.GenDecl)
  		if !ok || d.Tok != token.IMPORT {
  			// Not an import declaration, so we're done.
  			// Imports are always first.
  			return false
  		if d.Lparen.IsValid() {
  			// For now assume all grouped imports are unsorted.
  			// TODO(gri) Should check if they are sorted already.
  			return true
  		// Ungrouped imports are sorted by default.
  	return false

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