go printer 源码
golang printer 代码
文件路径：/src/cmd/compile/internal/syntax/printer.go
// 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, "<bad expr>")
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, _Type)
}
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, _Func)
}
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, 0)
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, 0)
}
}
}
// If tok != 0 print a type parameter list: tok == _Type means
// a type parameter list for a type, tok == _Func means a type
// parameter list for a func.
func (p *printer) printParameterList(list []*Field, tok token) {
open, close := _Lparen, _Rparen
if tok != 0 {
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 the name P and the type expression T syntactically
// combine to another valid (value) expression requires a trailing comma, as in [P *T,]
// (or an enclosing interface as in [P interface(*T)]), so that the type parameter list
// is not parsed as an array length [P*T].
if tok == _Type && len(list) == 1 && combinesWithName(list[0].Type) {
p.print(_Comma)
}
p.print(close)
}
// combinesWithName reports whether a name followed by the expression x
// syntactically combines to another valid (value) expression. For instance
// using *T for x, "name *T" syntactically appears as the expression x*T.
// On the other hand, using P|Q or *P|~Q for x, "name P|Q" or name *P|~Q"
// cannot be combined into a valid (value) expression.
func combinesWithName(x Expr) bool {
switch x := x.(type) {
case *Operation:
if x.Y == nil {
// name *x.X combines to name*x.X if x.X is not a type element
return x.Op == Mul && !isTypeElem(x.X)
}
// binary expressions
return combinesWithName(x.X) && !isTypeElem(x.Y)
case *ParenExpr:
// name(x) combines but we are making sure at
// the call site that x is never parenthesized.
panic("unexpected parenthesized expression")
}
return false
}
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)
}
}
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