1 // Copyright 2012 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package format implements standard formatting of Go source. 6 // 7 // Note that formatting of Go source code changes over time, so tools relying on 8 // consistent formatting should execute a specific version of the gofmt binary 9 // instead of using this package. That way, the formatting will be stable, and 10 // the tools won't need to be recompiled each time gofmt changes. 11 // 12 // For example, pre-submit checks that use this package directly would behave 13 // differently depending on what Go version each developer uses, causing the 14 // check to be inherently fragile. 15 package format 16 17 import ( 18 "bytes" 19 "fmt" 20 "go/ast" 21 "go/parser" 22 "go/printer" 23 "go/token" 24 "io" 25 ) 26 27 var config = printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8} 28 29 const parserMode = parser.ParseComments 30 31 // Node formats node in canonical gofmt style and writes the result to dst. 32 // 33 // The node type must be *ast.File, *printer.CommentedNode, []ast.Decl, 34 // []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec, 35 // or ast.Stmt. Node does not modify node. Imports are not sorted for 36 // nodes representing partial source files (for instance, if the node is 37 // not an *ast.File or a *printer.CommentedNode not wrapping an *ast.File). 38 // 39 // The function may return early (before the entire result is written) 40 // and return a formatting error, for instance due to an incorrect AST. 41 // 42 func Node(dst io.Writer, fset *token.FileSet, node interface{}) error { 43 // Determine if we have a complete source file (file != nil). 44 var file *ast.File 45 var cnode *printer.CommentedNode 46 switch n := node.(type) { 47 case *ast.File: 48 file = n 49 case *printer.CommentedNode: 50 if f, ok := n.Node.(*ast.File); ok { 51 file = f 52 cnode = n 53 } 54 } 55 56 // Sort imports if necessary. 57 if file != nil && hasUnsortedImports(file) { 58 // Make a copy of the AST because ast.SortImports is destructive. 59 // TODO(gri) Do this more efficiently. 60 var buf bytes.Buffer 61 err := config.Fprint(&buf, fset, file) 62 if err != nil { 63 return err 64 } 65 file, err = parser.ParseFile(fset, "", buf.Bytes(), parserMode) 66 if err != nil { 67 // We should never get here. If we do, provide good diagnostic. 68 return fmt.Errorf("format.Node internal error (%s)", err) 69 } 70 ast.SortImports(fset, file) 71 72 // Use new file with sorted imports. 73 node = file 74 if cnode != nil { 75 node = &printer.CommentedNode{Node: file, Comments: cnode.Comments} 76 } 77 } 78 79 return config.Fprint(dst, fset, node) 80 } 81 82 // Source formats src in canonical gofmt style and returns the result 83 // or an (I/O or syntax) error. src is expected to be a syntactically 84 // correct Go source file, or a list of Go declarations or statements. 85 // 86 // If src is a partial source file, the leading and trailing space of src 87 // is applied to the result (such that it has the same leading and trailing 88 // space as src), and the result is indented by the same amount as the first 89 // line of src containing code. Imports are not sorted for partial source files. 90 // 91 func Source(src []byte) ([]byte, error) { 92 fset := token.NewFileSet() 93 file, sourceAdj, indentAdj, err := parse(fset, "", src, true) 94 if err != nil { 95 return nil, err 96 } 97 98 if sourceAdj == nil { 99 // Complete source file. 100 // TODO(gri) consider doing this always. 101 ast.SortImports(fset, file) 102 } 103 104 return format(fset, file, sourceAdj, indentAdj, src, config) 105 } 106 107 func hasUnsortedImports(file *ast.File) bool { 108 for _, d := range file.Decls { 109 d, ok := d.(*ast.GenDecl) 110 if !ok || d.Tok != token.IMPORT { 111 // Not an import declaration, so we're done. 112 // Imports are always first. 113 return false 114 } 115 if d.Lparen.IsValid() { 116 // For now assume all grouped imports are unsorted. 117 // TODO(gri) Should check if they are sorted already. 118 return true 119 } 120 // Ungrouped imports are sorted by default. 121 } 122 return false 123 } 124