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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.
//
// 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 (
"bytes"
"fmt"
"go/ast"
"go/parser"
"go/printer"
"go/token"
"io"
)
// Keep these in sync with cmd/gofmt/gofmt.go.
const (
tabWidth = 8
printerMode = printer.UseSpaces | printer.TabIndent | printerNormalizeNumbers
// printerNormalizeNumbers means to canonicalize number literal prefixes
// and exponents while printing. See https://golang.org/doc/go1.13#gofmt.
//
// This value is defined in go/printer specifically for go/format and cmd/gofmt.
printerNormalizeNumbers = 1 << 30
)
var config = printer.Config{Mode: printerMode, Tabwidth: tabWidth}
const parserMode = parser.ParseComments | parser.SkipObjectResolution
// 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 any) 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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