// Copyright 2016 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. // This file implements printing of syntax trees in source format. package syntax import ( "bytes" "fmt" "io" "strings" ) // Form controls print formatting. type Form uint const ( _ Form = iota // default LineForm // use spaces instead of linebreaks where possible ShortForm // like LineForm but print "…" for non-empty function or composite literal bodies ) // Fprint prints node x to w in the specified form. // It returns the number of bytes written, and whether there was an error. func Fprint(w io.Writer, x Node, form Form) (n int, err error) { p := printer{ output: w, form: form, linebreaks: form == 0, } defer func() { n = p.written if e := recover(); e != nil { err = e.(writeError).err // re-panics if it's not a writeError } }() p.print(x) p.flush(_EOF) return } // String is a convenience function that prints n in ShortForm // and returns the printed string. func String(n Node) string { var buf bytes.Buffer _, err := Fprint(&buf, n, ShortForm) if err != nil { fmt.Fprintf(&buf, "<<< ERROR: %s", err) } return buf.String() } type ctrlSymbol int const ( none ctrlSymbol = iota semi blank newline indent outdent // comment // eolComment ) type whitespace struct { last token kind ctrlSymbol //text string // comment text (possibly ""); valid if kind == comment } type printer struct { output io.Writer written int // number of bytes written form Form linebreaks bool // print linebreaks instead of semis indent int // current indentation level nlcount int // number of consecutive newlines pending []whitespace // pending whitespace lastTok token // last token (after any pending semi) processed by print } // write is a thin wrapper around p.output.Write // that takes care of accounting and error handling. func (p *printer) write(data []byte) { n, err := p.output.Write(data) p.written += n if err != nil { panic(writeError{err}) } } var ( tabBytes = []byte("\t\t\t\t\t\t\t\t") newlineByte = []byte("\n") blankByte = []byte(" ") ) func (p *printer) writeBytes(data []byte) { if len(data) == 0 { panic("expected non-empty []byte") } if p.nlcount > 0 && p.indent > 0 { // write indentation n := p.indent for n > len(tabBytes) { p.write(tabBytes) n -= len(tabBytes) } p.write(tabBytes[:n]) } p.write(data) p.nlcount = 0 } func (p *printer) writeString(s string) { p.writeBytes([]byte(s)) } // If impliesSemi returns true for a non-blank line's final token tok, // a semicolon is automatically inserted. Vice versa, a semicolon may // be omitted in those cases. func impliesSemi(tok token) bool { switch tok { case _Name, _Break, _Continue, _Fallthrough, _Return, /*_Inc, _Dec,*/ _Rparen, _Rbrack, _Rbrace: // TODO(gri) fix this return true } return false } // TODO(gri) provide table of []byte values for all tokens to avoid repeated string conversion func lineComment(text string) bool { return strings.HasPrefix(text, "//") } func (p *printer) addWhitespace(kind ctrlSymbol, text string) { p.pending = append(p.pending, whitespace{p.lastTok, kind /*text*/}) switch kind { case semi: p.lastTok = _Semi case newline: p.lastTok = 0 // TODO(gri) do we need to handle /*-style comments containing newlines here? } } func (p *printer) flush(next token) { // eliminate semis and redundant whitespace sawNewline := next == _EOF sawParen := next == _Rparen || next == _Rbrace for i := len(p.pending) - 1; i >= 0; i-- { switch p.pending[i].kind { case semi: k := semi if sawParen { sawParen = false k = none // eliminate semi } else if sawNewline && impliesSemi(p.pending[i].last) { sawNewline = false k = none // eliminate semi } p.pending[i].kind = k case newline: sawNewline = true case blank, indent, outdent: // nothing to do // case comment: // // A multi-line comment acts like a newline; and a "" // // comment implies by definition at least one newline. // if text := p.pending[i].text; strings.HasPrefix(text, "/*") && strings.ContainsRune(text, '\n') { // sawNewline = true // } // case eolComment: // // TODO(gri) act depending on sawNewline default: panic("unreachable") } } // print pending prev := none for i := range p.pending { switch p.pending[i].kind { case none: // nothing to do case semi: p.writeString(";") p.nlcount = 0 prev = semi case blank: if prev != blank { // at most one blank p.writeBytes(blankByte) p.nlcount = 0 prev = blank } case newline: const maxEmptyLines = 1 if p.nlcount <= maxEmptyLines { p.write(newlineByte) p.nlcount++ prev = newline } case indent: p.indent++ case outdent: p.indent-- if p.indent < 0 { panic("negative indentation") } // case comment: // if text := p.pending[i].text; text != "" { // p.writeString(text) // p.nlcount = 0 // prev = comment // } // // TODO(gri) should check that line comments are always followed by newline default: panic("unreachable") } } p.pending = p.pending[:0] // re-use underlying array } func mayCombine(prev token, next byte) (b bool) { return // for now // switch prev { // case lexical.Int: // b = next == '.' // 1. // case lexical.Add: // b = next == '+' // ++ // case lexical.Sub: // b = next == '-' // -- // case lexical.Quo: // b = next == '*' // /* // case lexical.Lss: // b = next == '-' || next == '<' // <- or << // case lexical.And: // b = next == '&' || next == '^' // && or &^ // } // return } func (p *printer) print(args ...interface{}) { for i := 0; i < len(args); i++ { switch x := args[i].(type) { case nil: // we should not reach here but don't crash case Node: p.printNode(x) case token: // _Name implies an immediately following string // argument which is the actual value to print. var s string if x == _Name { i++ if i >= len(args) { panic("missing string argument after _Name") } s = args[i].(string) } else { s = x.String() } // TODO(gri) This check seems at the wrong place since it doesn't // take into account pending white space. if mayCombine(p.lastTok, s[0]) { panic("adjacent tokens combine without whitespace") } if x == _Semi { // delay printing of semi p.addWhitespace(semi, "") } else { p.flush(x) p.writeString(s) p.nlcount = 0 p.lastTok = x } case Operator: if x != 0 { p.flush(_Operator) p.writeString(x.String()) } case ctrlSymbol: switch x { case none, semi /*, comment*/ : panic("unreachable") case newline: // TODO(gri) need to handle mandatory newlines after a //-style comment if !p.linebreaks { x = blank } } p.addWhitespace(x, "") // case *Comment: // comments are not Nodes // p.addWhitespace(comment, x.Text) default: panic(fmt.Sprintf("unexpected argument %v (%T)", x, x)) } } } func (p *printer) printNode(n Node) { // ncom := *n.Comments() // if ncom != nil { // // TODO(gri) in general we cannot make assumptions about whether // // a comment is a /*- or a //-style comment since the syntax // // tree may have been manipulated. Need to make sure the correct // // whitespace is emitted. // for _, c := range ncom.Alone { // p.print(c, newline) // } // for _, c := range ncom.Before { // if c.Text == "" || lineComment(c.Text) { // panic("unexpected empty line or //-style 'before' comment") // } // p.print(c, blank) // } // } p.printRawNode(n) // if ncom != nil && len(ncom.After) > 0 { // for i, c := range ncom.After { // if i+1 < len(ncom.After) { // if c.Text == "" || lineComment(c.Text) { // panic("unexpected empty line or //-style non-final 'after' comment") // } // } // p.print(blank, c) // } // //p.print(newline) // } } func (p *printer) printRawNode(n Node) { switch n := n.(type) { case nil: // we should not reach here but don't crash // expressions and types case *BadExpr: p.print(_Name, "") case *Name: p.print(_Name, n.Value) // _Name requires actual value following immediately case *BasicLit: p.print(_Name, n.Value) // _Name requires actual value following immediately case *FuncLit: p.print(n.Type, blank) if n.Body != nil { if p.form == ShortForm { p.print(_Lbrace) if len(n.Body.List) > 0 { p.print(_Name, "…") } p.print(_Rbrace) } else { p.print(n.Body) } } case *CompositeLit: if n.Type != nil { p.print(n.Type) } p.print(_Lbrace) if p.form == ShortForm { if len(n.ElemList) > 0 { p.print(_Name, "…") } } else { if n.NKeys > 0 && n.NKeys == len(n.ElemList) { p.printExprLines(n.ElemList) } else { p.printExprList(n.ElemList) } } p.print(_Rbrace) case *ParenExpr: p.print(_Lparen, n.X, _Rparen) case *SelectorExpr: p.print(n.X, _Dot, n.Sel) case *IndexExpr: p.print(n.X, _Lbrack, n.Index, _Rbrack) case *SliceExpr: p.print(n.X, _Lbrack) if i := n.Index[0]; i != nil { p.printNode(i) } p.print(_Colon) if j := n.Index[1]; j != nil { p.printNode(j) } if k := n.Index[2]; k != nil { p.print(_Colon, k) } p.print(_Rbrack) case *AssertExpr: p.print(n.X, _Dot, _Lparen, n.Type, _Rparen) case *TypeSwitchGuard: if n.Lhs != nil { p.print(n.Lhs, blank, _Define, blank) } p.print(n.X, _Dot, _Lparen, _Type, _Rparen) case *CallExpr: p.print(n.Fun, _Lparen) p.printExprList(n.ArgList) if n.HasDots { p.print(_DotDotDot) } p.print(_Rparen) case *Operation: if n.Y == nil { // unary expr p.print(n.Op) // if n.Op == lexical.Range { // p.print(blank) // } p.print(n.X) } else { // binary expr // TODO(gri) eventually take precedence into account // to control possibly missing parentheses p.print(n.X, blank, n.Op, blank, n.Y) } case *KeyValueExpr: p.print(n.Key, _Colon, blank, n.Value) case *ListExpr: p.printExprList(n.ElemList) case *ArrayType: var len interface{} = _DotDotDot if n.Len != nil { len = n.Len } p.print(_Lbrack, len, _Rbrack, n.Elem) case *SliceType: p.print(_Lbrack, _Rbrack, n.Elem) case *DotsType: p.print(_DotDotDot, n.Elem) case *StructType: p.print(_Struct) if len(n.FieldList) > 0 && p.linebreaks { p.print(blank) } p.print(_Lbrace) if len(n.FieldList) > 0 { if p.linebreaks { p.print(newline, indent) p.printFieldList(n.FieldList, n.TagList, _Semi) p.print(outdent, newline) } else { p.printFieldList(n.FieldList, n.TagList, _Semi) } } p.print(_Rbrace) case *FuncType: p.print(_Func) p.printSignature(n) case *InterfaceType: p.print(_Interface) if p.linebreaks && len(n.MethodList) > 1 { p.print(blank) p.print(_Lbrace) p.print(newline, indent) p.printMethodList(n.MethodList) p.print(outdent, newline) } else { p.print(_Lbrace) p.printMethodList(n.MethodList) } p.print(_Rbrace) case *MapType: p.print(_Map, _Lbrack, n.Key, _Rbrack, n.Value) case *ChanType: if n.Dir == RecvOnly { p.print(_Arrow) } p.print(_Chan) if n.Dir == SendOnly { p.print(_Arrow) } p.print(blank) if e, _ := n.Elem.(*ChanType); n.Dir == 0 && e != nil && e.Dir == RecvOnly { // don't print chan (<-chan T) as chan <-chan T p.print(_Lparen) p.print(n.Elem) p.print(_Rparen) } else { p.print(n.Elem) } // statements case *DeclStmt: p.printDecl(n.DeclList) case *EmptyStmt: // nothing to print case *LabeledStmt: p.print(outdent, n.Label, _Colon, indent, newline, n.Stmt) case *ExprStmt: p.print(n.X) case *SendStmt: p.print(n.Chan, blank, _Arrow, blank, n.Value) case *AssignStmt: p.print(n.Lhs) if n.Rhs == nil { // TODO(gri) This is going to break the mayCombine // check once we enable that again. p.print(n.Op, n.Op) // ++ or -- } else { p.print(blank, n.Op, _Assign, blank) p.print(n.Rhs) } case *CallStmt: p.print(n.Tok, blank, n.Call) case *ReturnStmt: p.print(_Return) if n.Results != nil { p.print(blank, n.Results) } case *BranchStmt: p.print(n.Tok) if n.Label != nil { p.print(blank, n.Label) } case *BlockStmt: p.print(_Lbrace) if len(n.List) > 0 { p.print(newline, indent) p.printStmtList(n.List, true) p.print(outdent, newline) } p.print(_Rbrace) case *IfStmt: p.print(_If, blank) if n.Init != nil { p.print(n.Init, _Semi, blank) } p.print(n.Cond, blank, n.Then) if n.Else != nil { p.print(blank, _Else, blank, n.Else) } case *SwitchStmt: p.print(_Switch, blank) if n.Init != nil { p.print(n.Init, _Semi, blank) } if n.Tag != nil { p.print(n.Tag, blank) } p.printSwitchBody(n.Body) case *SelectStmt: p.print(_Select, blank) // for now p.printSelectBody(n.Body) case *RangeClause: if n.Lhs != nil { tok := _Assign if n.Def { tok = _Define } p.print(n.Lhs, blank, tok, blank) } p.print(_Range, blank, n.X) case *ForStmt: p.print(_For, blank) if n.Init == nil && n.Post == nil { if n.Cond != nil { p.print(n.Cond, blank) } } else { if n.Init != nil { p.print(n.Init) // TODO(gri) clean this up if _, ok := n.Init.(*RangeClause); ok { p.print(blank, n.Body) break } } p.print(_Semi, blank) if n.Cond != nil { p.print(n.Cond) } p.print(_Semi, blank) if n.Post != nil { p.print(n.Post, blank) } } p.print(n.Body) case *ImportDecl: if n.Group == nil { p.print(_Import, blank) } if n.LocalPkgName != nil { p.print(n.LocalPkgName, blank) } p.print(n.Path) case *ConstDecl: if n.Group == nil { p.print(_Const, blank) } p.printNameList(n.NameList) if n.Type != nil { p.print(blank, n.Type) } if n.Values != nil { p.print(blank, _Assign, blank, n.Values) } case *TypeDecl: if n.Group == nil { p.print(_Type, blank) } p.print(n.Name) if n.TParamList != nil { p.printParameterList(n.TParamList, true) } p.print(blank) if n.Alias { p.print(_Assign, blank) } p.print(n.Type) case *VarDecl: if n.Group == nil { p.print(_Var, blank) } p.printNameList(n.NameList) if n.Type != nil { p.print(blank, n.Type) } if n.Values != nil { p.print(blank, _Assign, blank, n.Values) } case *FuncDecl: p.print(_Func, blank) if r := n.Recv; r != nil { p.print(_Lparen) if r.Name != nil { p.print(r.Name, blank) } p.printNode(r.Type) p.print(_Rparen, blank) } p.print(n.Name) if n.TParamList != nil { p.printParameterList(n.TParamList, true) } p.printSignature(n.Type) if n.Body != nil { p.print(blank, n.Body) } case *printGroup: p.print(n.Tok, blank, _Lparen) if len(n.Decls) > 0 { p.print(newline, indent) for _, d := range n.Decls { p.printNode(d) p.print(_Semi, newline) } p.print(outdent) } p.print(_Rparen) // files case *File: p.print(_Package, blank, n.PkgName) if len(n.DeclList) > 0 { p.print(_Semi, newline, newline) p.printDeclList(n.DeclList) } default: panic(fmt.Sprintf("syntax.Iterate: unexpected node type %T", n)) } } func (p *printer) printFields(fields []*Field, tags []*BasicLit, i, j int) { if i+1 == j && fields[i].Name == nil { // anonymous field p.printNode(fields[i].Type) } else { for k, f := range fields[i:j] { if k > 0 { p.print(_Comma, blank) } p.printNode(f.Name) } p.print(blank) p.printNode(fields[i].Type) } if i < len(tags) && tags[i] != nil { p.print(blank) p.printNode(tags[i]) } } func (p *printer) printFieldList(fields []*Field, tags []*BasicLit, sep token) { i0 := 0 var typ Expr for i, f := range fields { if f.Name == nil || f.Type != typ { if i0 < i { p.printFields(fields, tags, i0, i) p.print(sep, newline) i0 = i } typ = f.Type } } p.printFields(fields, tags, i0, len(fields)) } func (p *printer) printMethodList(methods []*Field) { for i, m := range methods { if i > 0 { p.print(_Semi, newline) } if m.Name != nil { p.printNode(m.Name) p.printSignature(m.Type.(*FuncType)) } else { p.printNode(m.Type) } } } func (p *printer) printNameList(list []*Name) { for i, x := range list { if i > 0 { p.print(_Comma, blank) } p.printNode(x) } } func (p *printer) printExprList(list []Expr) { for i, x := range list { if i > 0 { p.print(_Comma, blank) } p.printNode(x) } } func (p *printer) printExprLines(list []Expr) { if len(list) > 0 { p.print(newline, indent) for _, x := range list { p.print(x, _Comma, newline) } p.print(outdent) } } func groupFor(d Decl) (token, *Group) { switch d := d.(type) { case *ImportDecl: return _Import, d.Group case *ConstDecl: return _Const, d.Group case *TypeDecl: return _Type, d.Group case *VarDecl: return _Var, d.Group case *FuncDecl: return _Func, nil default: panic("unreachable") } } type printGroup struct { node Tok token Decls []Decl } func (p *printer) printDecl(list []Decl) { tok, group := groupFor(list[0]) if group == nil { if len(list) != 1 { panic("unreachable") } p.printNode(list[0]) return } // if _, ok := list[0].(*EmptyDecl); ok { // if len(list) != 1 { // panic("unreachable") // } // // TODO(gri) if there are comments inside the empty // // group, we may need to keep the list non-nil // list = nil // } // printGroup is here for consistent comment handling // (this is not yet used) var pg printGroup // *pg.Comments() = *group.Comments() pg.Tok = tok pg.Decls = list p.printNode(&pg) } func (p *printer) printDeclList(list []Decl) { i0 := 0 var tok token var group *Group for i, x := range list { if s, g := groupFor(x); g == nil || g != group { if i0 < i { p.printDecl(list[i0:i]) p.print(_Semi, newline) // print empty line between different declaration groups, // different kinds of declarations, or between functions if g != group || s != tok || s == _Func { p.print(newline) } i0 = i } tok, group = s, g } } p.printDecl(list[i0:]) } func (p *printer) printSignature(sig *FuncType) { p.printParameterList(sig.ParamList, false) if list := sig.ResultList; list != nil { p.print(blank) if len(list) == 1 && list[0].Name == nil { p.printNode(list[0].Type) } else { p.printParameterList(list, false) } } } func (p *printer) printParameterList(list []*Field, types bool) { open, close := _Lparen, _Rparen if types { open, close = _Lbrack, _Rbrack } p.print(open) for i, f := range list { if i > 0 { p.print(_Comma, blank) } if f.Name != nil { p.printNode(f.Name) if i+1 < len(list) { f1 := list[i+1] if f1.Name != nil && f1.Type == f.Type { continue // no need to print type } } p.print(blank) } p.printNode(unparen(f.Type)) // no need for (extra) parentheses around parameter types } // A type parameter list [P *T] where T is not a type literal requires a comma as in [P *T,] // so that it's not parsed as [P*T]. if types && len(list) == 1 { if t, _ := list[0].Type.(*Operation); t != nil && t.Op == Mul && t.Y == nil && !isTypeLit(t.X) { p.print(_Comma) } } p.print(close) } func (p *printer) printStmtList(list []Stmt, braces bool) { for i, x := range list { p.print(x, _Semi) if i+1 < len(list) { p.print(newline) } else if braces { // Print an extra semicolon if the last statement is // an empty statement and we are in a braced block // because one semicolon is automatically removed. if _, ok := x.(*EmptyStmt); ok { p.print(x, _Semi) } } } } func (p *printer) printSwitchBody(list []*CaseClause) { p.print(_Lbrace) if len(list) > 0 { p.print(newline) for i, c := range list { p.printCaseClause(c, i+1 == len(list)) p.print(newline) } } p.print(_Rbrace) } func (p *printer) printSelectBody(list []*CommClause) { p.print(_Lbrace) if len(list) > 0 { p.print(newline) for i, c := range list { p.printCommClause(c, i+1 == len(list)) p.print(newline) } } p.print(_Rbrace) } func (p *printer) printCaseClause(c *CaseClause, braces bool) { if c.Cases != nil { p.print(_Case, blank, c.Cases) } else { p.print(_Default) } p.print(_Colon) if len(c.Body) > 0 { p.print(newline, indent) p.printStmtList(c.Body, braces) p.print(outdent) } } func (p *printer) printCommClause(c *CommClause, braces bool) { if c.Comm != nil { p.print(_Case, blank) p.print(c.Comm) } else { p.print(_Default) } p.print(_Colon) if len(c.Body) > 0 { p.print(newline, indent) p.printStmtList(c.Body, braces) p.print(outdent) } }