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// 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.
package format
import (
"bytes"
"fmt"
"go/ast"
"go/parser"
"go/printer"
"go/token"
"io"
"strings"
)
var config = printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
// 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 (i.e., 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(), parser.ParseComments)
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 writes the result to dst
// or returns 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 formatted src 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()
node, err := parse(fset, src)
if err != nil {
return nil, err
}
var buf bytes.Buffer
if file, ok := node.(*ast.File); ok {
// Complete source file.
ast.SortImports(fset, file)
err := config.Fprint(&buf, fset, file)
if err != nil {
return nil, err
}
} else {
// Partial source file.
// Determine and prepend leading space.
i, j := 0, 0
for j < len(src) && isSpace(src[j]) {
if src[j] == '\n' {
i = j + 1 // index of last line in leading space
}
j++
}
buf.Write(src[:i])
// Determine indentation of first code line.
// Spaces are ignored unless there are no tabs,
// in which case spaces count as one tab.
indent := 0
hasSpace := false
for _, b := range src[i:j] {
switch b {
case ' ':
hasSpace = true
case '\t':
indent++
}
}
if indent == 0 && hasSpace {
indent = 1
}
// Format the source.
cfg := config
cfg.Indent = indent
err := cfg.Fprint(&buf, fset, node)
if err != nil {
return nil, err
}
// Determine and append trailing space.
i = len(src)
for i > 0 && isSpace(src[i-1]) {
i--
}
buf.Write(src[i:])
}
return buf.Bytes(), nil
}
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
}
func isSpace(b byte) bool {
return b == ' ' || b == '\t' || b == '\n' || b == '\r'
}
func parse(fset *token.FileSet, src []byte) (interface{}, error) {
// Try as a complete source file.
file, err := parser.ParseFile(fset, "", src, parser.ParseComments)
if err == nil {
return file, nil
}
// If the source is missing a package clause, try as a source fragment; otherwise fail.
if !strings.Contains(err.Error(), "expected 'package'") {
return nil, err
}
// Try as a declaration list by prepending a package clause in front of src.
// Use ';' not '\n' to keep line numbers intact.
psrc := append([]byte("package p;"), src...)
file, err = parser.ParseFile(fset, "", psrc, parser.ParseComments)
if err == nil {
return file.Decls, nil
}
// If the source is missing a declaration, try as a statement list; otherwise fail.
if !strings.Contains(err.Error(), "expected declaration") {
return nil, err
}
// Try as statement list by wrapping a function around src.
fsrc := append(append([]byte("package p; func _() {"), src...), '}')
file, err = parser.ParseFile(fset, "", fsrc, parser.ParseComments)
if err == nil {
return file.Decls[0].(*ast.FuncDecl).Body.List, nil
}
// Failed, and out of options.
return nil, err
}
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