// Copyright 2009 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 AST nodes; specifically
// expressions, statements, declarations, and files. It uses
// the print functionality implemented in printer.go.
package printer
import (
"bytes"
"go/ast"
"go/token"
"math"
"strconv"
"strings"
"unicode"
"unicode/utf8"
)
// Formatting issues:
// - better comment formatting for /*-style comments at the end of a line (e.g. a declaration)
// when the comment spans multiple lines; if such a comment is just two lines, formatting is
// not idempotent
// - formatting of expression lists
// - should use blank instead of tab to separate one-line function bodies from
// the function header unless there is a group of consecutive one-liners
// ----------------------------------------------------------------------------
// Common AST nodes.
// Print as many newlines as necessary (but at least min newlines) to get to
// the current line. ws is printed before the first line break. If newSection
// is set, the first line break is printed as formfeed. Returns 0 if no line
// breaks were printed, returns 1 if there was exactly one newline printed,
// and returns a value > 1 if there was a formfeed or more than one newline
// printed.
//
// TODO(gri): linebreak may add too many lines if the next statement at "line"
// is preceded by comments because the computation of n assumes
// the current position before the comment and the target position
// after the comment. Thus, after interspersing such comments, the
// space taken up by them is not considered to reduce the number of
// linebreaks. At the moment there is no easy way to know about
// future (not yet interspersed) comments in this function.
//
func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (nbreaks int) {
n := nlimit(line - p.pos.Line)
if n < min {
n = min
}
if n > 0 {
p.print(ws)
if newSection {
p.print(formfeed)
n--
nbreaks = 2
}
nbreaks += n
for ; n > 0; n-- {
p.print(newline)
}
}
return
}
// setComment sets g as the next comment if g != nil and if node comments
// are enabled - this mode is used when printing source code fragments such
// as exports only. It assumes that there is no pending comment in p.comments
// and at most one pending comment in the p.comment cache.
func (p *printer) setComment(g *ast.CommentGroup) {
if g == nil || !p.useNodeComments {
return
}
if p.comments == nil {
// initialize p.comments lazily
p.comments = make([]*ast.CommentGroup, 1)
} else if p.cindex < len(p.comments) {
// for some reason there are pending comments; this
// should never happen - handle gracefully and flush
// all comments up to g, ignore anything after that
p.flush(p.posFor(g.List[0].Pos()), token.ILLEGAL)
p.comments = p.comments[0:1]
// in debug mode, report error
p.internalError("setComment found pending comments")
}
p.comments[0] = g
p.cindex = 0
// don't overwrite any pending comment in the p.comment cache
// (there may be a pending comment when a line comment is
// immediately followed by a lead comment with no other
// tokens between)
if p.commentOffset == infinity {
p.nextComment() // get comment ready for use
}
}
type exprListMode uint
const (
commaTerm exprListMode = 1 << iota // list is optionally terminated by a comma
noIndent // no extra indentation in multi-line lists
)
// If indent is set, a multi-line identifier list is indented after the
// first linebreak encountered.
func (p *printer) identList(list []*ast.Ident, indent bool) {
// convert into an expression list so we can re-use exprList formatting
xlist := make([]ast.Expr, len(list))
for i, x := range list {
xlist[i] = x
}
var mode exprListMode
if !indent {
mode = noIndent
}
p.exprList(token.NoPos, xlist, 1, mode, token.NoPos, false)
}
const filteredMsg = "contains filtered or unexported fields"
// Print a list of expressions. If the list spans multiple
// source lines, the original line breaks are respected between
// expressions.
//
// TODO(gri) Consider rewriting this to be independent of []ast.Expr
// so that we can use the algorithm for any kind of list
// (e.g., pass list via a channel over which to range).
func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exprListMode, next0 token.Pos, isIncomplete bool) {
if len(list) == 0 {
if isIncomplete {
prev := p.posFor(prev0)
next := p.posFor(next0)
if prev.IsValid() && prev.Line == next.Line {
p.print("/* " + filteredMsg + " */")
} else {
p.print(newline)
p.print(indent, "// "+filteredMsg, unindent, newline)
}
}
return
}
prev := p.posFor(prev0)
next := p.posFor(next0)
line := p.lineFor(list[0].Pos())
endLine := p.lineFor(list[len(list)-1].End())
if prev.IsValid() && prev.Line == line && line == endLine {
// all list entries on a single line
for i, x := range list {
if i > 0 {
// use position of expression following the comma as
// comma position for correct comment placement
p.print(x.Pos(), token.COMMA, blank)
}
p.expr0(x, depth)
}
if isIncomplete {
p.print(token.COMMA, blank, "/* "+filteredMsg+" */")
}
return
}
// list entries span multiple lines;
// use source code positions to guide line breaks
// Don't add extra indentation if noIndent is set;
// i.e., pretend that the first line is already indented.
ws := ignore
if mode&noIndent == 0 {
ws = indent
}
// The first linebreak is always a formfeed since this section must not
// depend on any previous formatting.
prevBreak := -1 // index of last expression that was followed by a linebreak
if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) > 0 {
ws = ignore
prevBreak = 0
}
// initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
size := 0
// We use the ratio between the geometric mean of the previous key sizes and
// the current size to determine if there should be a break in the alignment.
// To compute the geometric mean we accumulate the ln(size) values (lnsum)
// and the number of sizes included (count).
lnsum := 0.0
count := 0
// print all list elements
prevLine := prev.Line
for i, x := range list {
line = p.lineFor(x.Pos())
// Determine if the next linebreak, if any, needs to use formfeed:
// in general, use the entire node size to make the decision; for
// key:value expressions, use the key size.
// TODO(gri) for a better result, should probably incorporate both
// the key and the node size into the decision process
useFF := true
// Determine element size: All bets are off if we don't have
// position information for the previous and next token (likely
// generated code - simply ignore the size in this case by setting
// it to 0).
prevSize := size
const infinity = 1e6 // larger than any source line
size = p.nodeSize(x, infinity)
pair, isPair := x.(*ast.KeyValueExpr)
if size <= infinity && prev.IsValid() && next.IsValid() {
// x fits on a single line
if isPair {
size = p.nodeSize(pair.Key, infinity) // size <= infinity
}
} else {
// size too large or we don't have good layout information
size = 0
}
// If the previous line and the current line had single-
// line-expressions and the key sizes are small or the
// ratio between the current key and the geometric mean
// if the previous key sizes does not exceed a threshold,
// align columns and do not use formfeed.
if prevSize > 0 && size > 0 {
const smallSize = 40
if count == 0 || prevSize <= smallSize && size <= smallSize {
useFF = false
} else {
const r = 2.5 // threshold
geomean := math.Exp(lnsum / float64(count)) // count > 0
ratio := float64(size) / geomean
useFF = r*ratio <= 1 || r <= ratio
}
}
needsLinebreak := 0 < prevLine && prevLine < line
if i > 0 {
// Use position of expression following the comma as
// comma position for correct comment placement, but
// only if the expression is on the same line.
if !needsLinebreak {
p.print(x.Pos())
}
p.print(token.COMMA)
needsBlank := true
if needsLinebreak {
// Lines are broken using newlines so comments remain aligned
// unless useFF is set or there are multiple expressions on
// the same line in which case formfeed is used.
nbreaks := p.linebreak(line, 0, ws, useFF || prevBreak+1 < i)
if nbreaks > 0 {
ws = ignore
prevBreak = i
needsBlank = false // we got a line break instead
}
// If there was a new section or more than one new line
// (which means that the tabwriter will implicitly break
// the section), reset the geomean variables since we are
// starting a new group of elements with the next element.
if nbreaks > 1 {
lnsum = 0
count = 0
}
}
if needsBlank {
p.print(blank)
}
}
if len(list) > 1 && isPair && size > 0 && needsLinebreak {
// We have a key:value expression that fits onto one line
// and it's not on the same line as the prior expression:
// Use a column for the key such that consecutive entries
// can align if possible.
// (needsLinebreak is set if we started a new line before)
p.expr(pair.Key)
p.print(pair.Colon, token.COLON, vtab)
p.expr(pair.Value)
} else {
p.expr0(x, depth)
}
if size > 0 {
lnsum += math.Log(float64(size))
count++
}
prevLine = line
}
if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {
// Print a terminating comma if the next token is on a new line.
p.print(token.COMMA)
if isIncomplete {
p.print(newline)
p.print("// " + filteredMsg)
}
if ws == ignore && mode&noIndent == 0 {
// unindent if we indented
p.print(unindent)
}
p.print(formfeed) // terminating comma needs a line break to look good
return
}
if isIncomplete {
p.print(token.COMMA, newline)
p.print("// "+filteredMsg, newline)
}
if ws == ignore && mode&noIndent == 0 {
// unindent if we indented
p.print(unindent)
}
}
func (p *printer) parameters(fields *ast.FieldList) {
p.print(fields.Opening, token.LPAREN)
if len(fields.List) > 0 {
prevLine := p.lineFor(fields.Opening)
ws := indent
for i, par := range fields.List {
// determine par begin and end line (may be different
// if there are multiple parameter names for this par
// or the type is on a separate line)
var parLineBeg int
if len(par.Names) > 0 {
parLineBeg = p.lineFor(par.Names[0].Pos())
} else {
parLineBeg = p.lineFor(par.Type.Pos())
}
var parLineEnd = p.lineFor(par.Type.End())
// separating "," if needed
needsLinebreak := 0 < prevLine && prevLine < parLineBeg
if i > 0 {
// use position of parameter following the comma as
// comma position for correct comma placement, but
// only if the next parameter is on the same line
if !needsLinebreak {
p.print(par.Pos())
}
p.print(token.COMMA)
}
// separator if needed (linebreak or blank)
if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
// break line if the opening "(" or previous parameter ended on a different line
ws = ignore
} else if i > 0 {
p.print(blank)
}
// parameter names
if len(par.Names) > 0 {
// Very subtle: If we indented before (ws == ignore), identList
// won't indent again. If we didn't (ws == indent), identList will
// indent if the identList spans multiple lines, and it will outdent
// again at the end (and still ws == indent). Thus, a subsequent indent
// by a linebreak call after a type, or in the next multi-line identList
// will do the right thing.
p.identList(par.Names, ws == indent)
p.print(blank)
}
// parameter type
p.expr(stripParensAlways(par.Type))
prevLine = parLineEnd
}
// if the closing ")" is on a separate line from the last parameter,
// print an additional "," and line break
if closing := p.lineFor(fields.Closing); 0 < prevLine && prevLine < closing {
p.print(token.COMMA)
p.linebreak(closing, 0, ignore, true)
}
// unindent if we indented
if ws == ignore {
p.print(unindent)
}
}
p.print(fields.Closing, token.RPAREN)
}
func (p *printer) signature(params, result *ast.FieldList) {
if params != nil {
p.parameters(params)
} else {
p.print(token.LPAREN, token.RPAREN)
}
n := result.NumFields()
if n > 0 {
// result != nil
p.print(blank)
if n == 1 && result.List[0].Names == nil {
// single anonymous result; no ()'s
p.expr(stripParensAlways(result.List[0].Type))
return
}
p.parameters(result)
}
}
func identListSize(list []*ast.Ident, maxSize int) (size int) {
for i, x := range list {
if i > 0 {
size += len(", ")
}
size += utf8.RuneCountInString(x.Name)
if size >= maxSize {
break
}
}
return
}
func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
if len(list) != 1 {
return false // allow only one field
}
f := list[0]
if f.Tag != nil || f.Comment != nil {
return false // don't allow tags or comments
}
// only name(s) and type
const maxSize = 30 // adjust as appropriate, this is an approximate value
namesSize := identListSize(f.Names, maxSize)
if namesSize > 0 {
namesSize = 1 // blank between names and types
}
typeSize := p.nodeSize(f.Type, maxSize)
return namesSize+typeSize <= maxSize
}
func (p *printer) setLineComment(text string) {
p.setComment(&ast.CommentGroup{List: []*ast.Comment{{Slash: token.NoPos, Text: text}}})
}
func (p *printer) fieldList(fields *ast.FieldList, isStruct, isIncomplete bool) {
lbrace := fields.Opening
list := fields.List
rbrace := fields.Closing
hasComments := isIncomplete || p.commentBefore(p.posFor(rbrace))
srcIsOneLine := lbrace.IsValid() && rbrace.IsValid() && p.lineFor(lbrace) == p.lineFor(rbrace)
if !hasComments && srcIsOneLine {
// possibly a one-line struct/interface
if len(list) == 0 {
// no blank between keyword and {} in this case
p.print(lbrace, token.LBRACE, rbrace, token.RBRACE)
return
} else if p.isOneLineFieldList(list) {
// small enough - print on one line
// (don't use identList and ignore source line breaks)
p.print(lbrace, token.LBRACE, blank)
f := list[0]
if isStruct {
for i, x := range f.Names {
if i > 0 {
// no comments so no need for comma position
p.print(token.COMMA, blank)
}
p.expr(x)
}
if len(f.Names) > 0 {
p.print(blank)
}
p.expr(f.Type)
} else { // interface
if ftyp, isFtyp := f.Type.(*ast.FuncType); isFtyp {
// method
p.expr(f.Names[0])
p.signature(ftyp.Params, ftyp.Results)
} else {
// embedded interface
p.expr(f.Type)
}
}
p.print(blank, rbrace, token.RBRACE)
return
}
}
// hasComments || !srcIsOneLine
p.print(blank, lbrace, token.LBRACE, indent)
if hasComments || len(list) > 0 {
p.print(formfeed)
}
if isStruct {
sep := vtab
if len(list) == 1 {
sep = blank
}
var line int
for i, f := range list {
if i > 0 {
p.linebreak(p.lineFor(f.Pos()), 1, ignore, p.linesFrom(line) > 0)
}
extraTabs := 0
p.setComment(f.Doc)
p.recordLine(&line)
if len(f.Names) > 0 {
// named fields
p.identList(f.Names, false)
p.print(sep)
p.expr(f.Type)
extraTabs = 1
} else {
// anonymous field
p.expr(f.Type)
extraTabs = 2
}
if f.Tag != nil {
if len(f.Names) > 0 && sep == vtab {
p.print(sep)
}
p.print(sep)
p.expr(f.Tag)
extraTabs = 0
}
if f.Comment != nil {
for ; extraTabs > 0; extraTabs-- {
p.print(sep)
}
p.setComment(f.Comment)
}
}
if isIncomplete {
if len(list) > 0 {
p.print(formfeed)
}
p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
p.setLineComment("// " + filteredMsg)
}
} else { // interface
var line int
for i, f := range list {
if i > 0 {
p.linebreak(p.lineFor(f.Pos()), 1, ignore, p.linesFrom(line) > 0)
}
p.setComment(f.Doc)
p.recordLine(&line)
if ftyp, isFtyp := f.Type.(*ast.FuncType); isFtyp {
// method
p.expr(f.Names[0])
p.signature(ftyp.Params, ftyp.Results)
} else {
// embedded interface
p.expr(f.Type)
}
p.setComment(f.Comment)
}
if isIncomplete {
if len(list) > 0 {
p.print(formfeed)
}
p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
p.setLineComment("// contains filtered or unexported methods")
}
}
p.print(unindent, formfeed, rbrace, token.RBRACE)
}
// ----------------------------------------------------------------------------
// Expressions
func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
switch e.Op.Precedence() {
case 4:
has4 = true
case 5:
has5 = true
}
switch l := e.X.(type) {
case *ast.BinaryExpr:
if l.Op.Precedence() < e.Op.Precedence() {
// parens will be inserted.
// pretend this is an *ast.ParenExpr and do nothing.
break
}
h4, h5, mp := walkBinary(l)
has4 = has4 || h4
has5 = has5 || h5
if maxProblem < mp {
maxProblem = mp
}
}
switch r := e.Y.(type) {
case *ast.BinaryExpr:
if r.Op.Precedence() <= e.Op.Precedence() {
// parens will be inserted.
// pretend this is an *ast.ParenExpr and do nothing.
break
}
h4, h5, mp := walkBinary(r)
has4 = has4 || h4
has5 = has5 || h5
if maxProblem < mp {
maxProblem = mp
}
case *ast.StarExpr:
if e.Op == token.QUO { // `*/`
maxProblem = 5
}
case *ast.UnaryExpr:
switch e.Op.String() + r.Op.String() {
case "/*", "&&", "&^":
maxProblem = 5
case "++", "--":
if maxProblem < 4 {
maxProblem = 4
}
}
}
return
}
func cutoff(e *ast.BinaryExpr, depth int) int {
has4, has5, maxProblem := walkBinary(e)
if maxProblem > 0 {
return maxProblem + 1
}
if has4 && has5 {
if depth == 1 {
return 5
}
return 4
}
if depth == 1 {
return 6
}
return 4
}
func diffPrec(expr ast.Expr, prec int) int {
x, ok := expr.(*ast.BinaryExpr)
if !ok || prec != x.Op.Precedence() {
return 1
}
return 0
}
func reduceDepth(depth int) int {
depth--
if depth < 1 {
depth = 1
}
return depth
}
// Format the binary expression: decide the cutoff and then format.
// Let's call depth == 1 Normal mode, and depth > 1 Compact mode.
// (Algorithm suggestion by Russ Cox.)
//
// The precedences are:
// 5 * / % << >> & &^
// 4 + - | ^
// 3 == != < <= > >=
// 2 &&
// 1 ||
//
// The only decision is whether there will be spaces around levels 4 and 5.
// There are never spaces at level 6 (unary), and always spaces at levels 3 and below.
//
// To choose the cutoff, look at the whole expression but excluding primary
// expressions (function calls, parenthesized exprs), and apply these rules:
//
// 1) If there is a binary operator with a right side unary operand
// that would clash without a space, the cutoff must be (in order):
//
// /* 6
// && 6
// &^ 6
// ++ 5
// -- 5
//
// (Comparison operators always have spaces around them.)
//
// 2) If there is a mix of level 5 and level 4 operators, then the cutoff
// is 5 (use spaces to distinguish precedence) in Normal mode
// and 4 (never use spaces) in Compact mode.
//
// 3) If there are no level 4 operators or no level 5 operators, then the
// cutoff is 6 (always use spaces) in Normal mode
// and 4 (never use spaces) in Compact mode.
//
func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int) {
prec := x.Op.Precedence()
if prec < prec1 {
// parenthesis needed
// Note: The parser inserts an ast.ParenExpr node; thus this case
// can only occur if the AST is created in a different way.
p.print(token.LPAREN)
p.expr0(x, reduceDepth(depth)) // parentheses undo one level of depth
p.print(token.RPAREN)
return
}
printBlank := prec < cutoff
ws := indent
p.expr1(x.X, prec, depth+diffPrec(x.X, prec))
if printBlank {
p.print(blank)
}
xline := p.pos.Line // before the operator (it may be on the next line!)
yline := p.lineFor(x.Y.Pos())
p.print(x.OpPos, x.Op)
if xline != yline && xline > 0 && yline > 0 {
// at least one line break, but respect an extra empty line
// in the source
if p.linebreak(yline, 1, ws, true) > 0 {
ws = ignore
printBlank = false // no blank after line break
}
}
if printBlank {
p.print(blank)
}
p.expr1(x.Y, prec+1, depth+1)
if ws == ignore {
p.print(unindent)
}
}
func isBinary(expr ast.Expr) bool {
_, ok := expr.(*ast.BinaryExpr)
return ok
}
func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
p.print(expr.Pos())
switch x := expr.(type) {
case *ast.BadExpr:
p.print("BadExpr")
case *ast.Ident:
p.print(x)
case *ast.BinaryExpr:
if depth < 1 {
p.internalError("depth < 1:", depth)
depth = 1
}
p.binaryExpr(x, prec1, cutoff(x, depth), depth)
case *ast.KeyValueExpr:
p.expr(x.Key)
p.print(x.Colon, token.COLON, blank)
p.expr(x.Value)
case *ast.StarExpr:
const prec = token.UnaryPrec
if prec < prec1 {
// parenthesis needed
p.print(token.LPAREN)
p.print(token.MUL)
p.expr(x.X)
p.print(token.RPAREN)
} else {
// no parenthesis needed
p.print(token.MUL)
p.expr(x.X)
}
case *ast.UnaryExpr:
const prec = token.UnaryPrec
if prec < prec1 {
// parenthesis needed
p.print(token.LPAREN)
p.expr(x)
p.print(token.RPAREN)
} else {
// no parenthesis needed
p.print(x.Op)
if x.Op == token.RANGE {
// TODO(gri) Remove this code if it cannot be reached.
p.print(blank)
}
p.expr1(x.X, prec, depth)
}
case *ast.BasicLit:
p.print(x)
case *ast.FuncLit:
p.expr(x.Type)
p.funcBody(p.distanceFrom(x.Type.Pos()), blank, x.Body)
case *ast.ParenExpr:
if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
// don't print parentheses around an already parenthesized expression
// TODO(gri) consider making this more general and incorporate precedence levels
p.expr0(x.X, depth)
} else {
p.print(token.LPAREN)
p.expr0(x.X, reduceDepth(depth)) // parentheses undo one level of depth
p.print(x.Rparen, token.RPAREN)
}
case *ast.SelectorExpr:
p.selectorExpr(x, depth, false)
case *ast.TypeAssertExpr:
p.expr1(x.X, token.HighestPrec, depth)
p.print(token.PERIOD, x.Lparen, token.LPAREN)
if x.Type != nil {
p.expr(x.Type)
} else {
p.print(token.TYPE)
}
p.print(x.Rparen, token.RPAREN)
case *ast.IndexExpr:
// TODO(gri): should treat[] like parentheses and undo one level of depth
p.expr1(x.X, token.HighestPrec, 1)
p.print(x.Lbrack, token.LBRACK)
p.expr0(x.Index, depth+1)
p.print(x.Rbrack, token.RBRACK)
case *ast.SliceExpr:
// TODO(gri): should treat[] like parentheses and undo one level of depth
p.expr1(x.X, token.HighestPrec, 1)
p.print(x.Lbrack, token.LBRACK)
indices := []ast.Expr{x.Low, x.High}
if x.Max != nil {
indices = append(indices, x.Max)
}
// determine if we need extra blanks around ':'
var needsBlanks bool
if depth <= 1 {
var indexCount int
var hasBinaries bool
for _, x := range indices {
if x != nil {
indexCount++
if isBinary(x) {
hasBinaries = true
}
}
}
if indexCount > 1 && hasBinaries {
needsBlanks = true
}
}
for i, x := range indices {
if i > 0 {
if indices[i-1] != nil && needsBlanks {
p.print(blank)
}
p.print(token.COLON)
if x != nil && needsBlanks {
p.print(blank)
}
}
if x != nil {
p.expr0(x, depth+1)
}
}
p.print(x.Rbrack, token.RBRACK)
case *ast.CallExpr:
if len(x.Args) > 1 {
depth++
}
var wasIndented bool
if _, ok := x.Fun.(*ast.FuncType); ok {
// conversions to literal function types require parentheses around the type
p.print(token.LPAREN)
wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
p.print(token.RPAREN)
} else {
wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
}
p.print(x.Lparen, token.LPAREN)
if x.Ellipsis.IsValid() {
p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis, false)
p.print(x.Ellipsis, token.ELLIPSIS)
if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
p.print(token.COMMA, formfeed)
}
} else {
p.exprList(x.Lparen, x.Args, depth, commaTerm, x.Rparen, false)
}
p.print(x.Rparen, token.RPAREN)
if wasIndented {
p.print(unindent)
}
case *ast.CompositeLit:
// composite literal elements that are composite literals themselves may have the type omitted
if x.Type != nil {
p.expr1(x.Type, token.HighestPrec, depth)
}
p.level++
p.print(x.Lbrace, token.LBRACE)
p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace, x.Incomplete)
// do not insert extra line break following a /*-style comment
// before the closing '}' as it might break the code if there
// is no trailing ','
mode := noExtraLinebreak
// do not insert extra blank following a /*-style comment
// before the closing '}' unless the literal is empty
if len(x.Elts) > 0 {
mode |= noExtraBlank
}
// need the initial indent to print lone comments with
// the proper level of indentation
p.print(indent, unindent, mode, x.Rbrace, token.RBRACE, mode)
p.level--
case *ast.Ellipsis:
p.print(token.ELLIPSIS)
if x.Elt != nil {
p.expr(x.Elt)
}
case *ast.ArrayType:
p.print(token.LBRACK)
if x.Len != nil {
p.expr(x.Len)
}
p.print(token.RBRACK)
p.expr(x.Elt)
case *ast.StructType:
p.print(token.STRUCT)
p.fieldList(x.Fields, true, x.Incomplete)
case *ast.FuncType:
p.print(token.FUNC)
p.signature(x.Params, x.Results)
case *ast.InterfaceType:
p.print(token.INTERFACE)
p.fieldList(x.Methods, false, x.Incomplete)
case *ast.MapType:
p.print(token.MAP, token.LBRACK)
p.expr(x.Key)
p.print(token.RBRACK)
p.expr(x.Value)
case *ast.ChanType:
switch x.Dir {
case ast.SEND | ast.RECV:
p.print(token.CHAN)
case ast.RECV:
p.print(token.ARROW, token.CHAN) // x.Arrow and x.Pos() are the same
case ast.SEND:
p.print(token.CHAN, x.Arrow, token.ARROW)
}
p.print(blank)
p.expr(x.Value)
default:
panic("unreachable")
}
}
func (p *printer) possibleSelectorExpr(expr ast.Expr, prec1, depth int) bool {
if x, ok := expr.(*ast.SelectorExpr); ok {
return p.selectorExpr(x, depth, true)
}
p.expr1(expr, prec1, depth)
return false
}
// selectorExpr handles an *ast.SelectorExpr node and reports whether x spans
// multiple lines.
func (p *printer) selectorExpr(x *ast.SelectorExpr, depth int, isMethod bool) bool {
p.expr1(x.X, token.HighestPrec, depth)
p.print(token.PERIOD)
if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
p.print(indent, newline, x.Sel.Pos(), x.Sel)
if !isMethod {
p.print(unindent)
}
return true
}
p.print(x.Sel.Pos(), x.Sel)
return false
}
func (p *printer) expr0(x ast.Expr, depth int) {
p.expr1(x, token.LowestPrec, depth)
}
func (p *printer) expr(x ast.Expr) {
const depth = 1
p.expr1(x, token.LowestPrec, depth)
}
// ----------------------------------------------------------------------------
// Statements
// Print the statement list indented, but without a newline after the last statement.
// Extra line breaks between statements in the source are respected but at most one
// empty line is printed between statements.
func (p *printer) stmtList(list []ast.Stmt, nindent int, nextIsRBrace bool) {
if nindent > 0 {
p.print(indent)
}
var line int
i := 0
for _, s := range list {
// ignore empty statements (was issue 3466)
if _, isEmpty := s.(*ast.EmptyStmt); !isEmpty {
// nindent == 0 only for lists of switch/select case clauses;
// in those cases each clause is a new section
if len(p.output) > 0 {
// only print line break if we are not at the beginning of the output
// (i.e., we are not printing only a partial program)
p.linebreak(p.lineFor(s.Pos()), 1, ignore, i == 0 || nindent == 0 || p.linesFrom(line) > 0)
}
p.recordLine(&line)
p.stmt(s, nextIsRBrace && i == len(list)-1)
// labeled statements put labels on a separate line, but here
// we only care about the start line of the actual statement
// without label - correct line for each label
for t := s; ; {
lt, _ := t.(*ast.LabeledStmt)
if lt == nil {
break
}
line++
t = lt.Stmt
}
i++
}
}
if nindent > 0 {
p.print(unindent)
}
}
// block prints an *ast.BlockStmt; it always spans at least two lines.
func (p *printer) block(b *ast.BlockStmt, nindent int) {
p.print(b.Lbrace, token.LBRACE)
p.stmtList(b.List, nindent, true)
p.linebreak(p.lineFor(b.Rbrace), 1, ignore, true)
p.print(b.Rbrace, token.RBRACE)
}
func isTypeName(x ast.Expr) bool {
switch t := x.(type) {
case *ast.Ident:
return true
case *ast.SelectorExpr:
return isTypeName(t.X)
}
return false
}
func stripParens(x ast.Expr) ast.Expr {
if px, strip := x.(*ast.ParenExpr); strip {
// parentheses must not be stripped if there are any
// unparenthesized composite literals starting with
// a type name
ast.Inspect(px.X, func(node ast.Node) bool {
switch x := node.(type) {
case *ast.ParenExpr:
// parentheses protect enclosed composite literals
return false
case *ast.CompositeLit:
if isTypeName(x.Type) {
strip = false // do not strip parentheses
}
return false
}
// in all other cases, keep inspecting
return true
})
if strip {
return stripParens(px.X)
}
}
return x
}
func stripParensAlways(x ast.Expr) ast.Expr {
if x, ok := x.(*ast.ParenExpr); ok {
return stripParensAlways(x.X)
}
return x
}
func (p *printer) controlClause(isForStmt bool, init ast.Stmt, expr ast.Expr, post ast.Stmt) {
p.print(blank)
needsBlank := false
if init == nil && post == nil {
// no semicolons required
if expr != nil {
p.expr(stripParens(expr))
needsBlank = true
}
} else {
// all semicolons required
// (they are not separators, print them explicitly)
if init != nil {
p.stmt(init, false)
}
p.print(token.SEMICOLON, blank)
if expr != nil {
p.expr(stripParens(expr))
needsBlank = true
}
if isForStmt {
p.print(token.SEMICOLON, blank)
needsBlank = false
if post != nil {
p.stmt(post, false)
needsBlank = true
}
}
}
if needsBlank {
p.print(blank)
}
}
// indentList reports whether an expression list would look better if it
// were indented wholesale (starting with the very first element, rather
// than starting at the first line break).
//
func (p *printer) indentList(list []ast.Expr) bool {
// Heuristic: indentList reports whether there are more than one multi-
// line element in the list, or if there is any element that is not
// starting on the same line as the previous one ends.
if len(list) >= 2 {
var b = p.lineFor(list[0].Pos())
var e = p.lineFor(list[len(list)-1].End())
if 0 < b && b < e {
// list spans multiple lines
n := 0 // multi-line element count
line := b
for _, x := range list {
xb := p.lineFor(x.Pos())
xe := p.lineFor(x.End())
if line < xb {
// x is not starting on the same
// line as the previous one ended
return true
}
if xb < xe {
// x is a multi-line element
n++
}
line = xe
}
return n > 1
}
}
return false
}
func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool) {
p.print(stmt.Pos())
switch s := stmt.(type) {
case *ast.BadStmt:
p.print("BadStmt")
case *ast.DeclStmt:
p.decl(s.Decl)
case *ast.EmptyStmt:
// nothing to do
case *ast.LabeledStmt:
// a "correcting" unindent immediately following a line break
// is applied before the line break if there is no comment
// between (see writeWhitespace)
p.print(unindent)
p.expr(s.Label)
p.print(s.Colon, token.COLON, indent)
if e, isEmpty := s.Stmt.(*ast.EmptyStmt); isEmpty {
if !nextIsRBrace {
p.print(newline, e.Pos(), token.SEMICOLON)
break
}
} else {
p.linebreak(p.lineFor(s.Stmt.Pos()), 1, ignore, true)
}
p.stmt(s.Stmt, nextIsRBrace)
case *ast.ExprStmt:
const depth = 1
p.expr0(s.X, depth)
case *ast.SendStmt:
const depth = 1
p.expr0(s.Chan, depth)
p.print(blank, s.Arrow, token.ARROW, blank)
p.expr0(s.Value, depth)
case *ast.IncDecStmt:
const depth = 1
p.expr0(s.X, depth+1)
p.print(s.TokPos, s.Tok)
case *ast.AssignStmt:
var depth = 1
if len(s.Lhs) > 1 && len(s.Rhs) > 1 {
depth++
}
p.exprList(s.Pos(), s.Lhs, depth, 0, s.TokPos, false)
p.print(blank, s.TokPos, s.Tok, blank)
p.exprList(s.TokPos, s.Rhs, depth, 0, token.NoPos, false)
case *ast.GoStmt:
p.print(token.GO, blank)
p.expr(s.Call)
case *ast.DeferStmt:
p.print(token.DEFER, blank)
p.expr(s.Call)
case *ast.ReturnStmt:
p.print(token.RETURN)
if s.Results != nil {
p.print(blank)
// Use indentList heuristic to make corner cases look
// better (issue 1207). A more systematic approach would
// always indent, but this would cause significant
// reformatting of the code base and not necessarily
// lead to more nicely formatted code in general.
if p.indentList(s.Results) {
p.print(indent)
p.exprList(s.Pos(), s.Results, 1, noIndent, token.NoPos, false)
p.print(unindent)
} else {
p.exprList(s.Pos(), s.Results, 1, 0, token.NoPos, false)
}
}
case *ast.BranchStmt:
p.print(s.Tok)
if s.Label != nil {
p.print(blank)
p.expr(s.Label)
}
case *ast.BlockStmt:
p.block(s, 1)
case *ast.IfStmt:
p.print(token.IF)
p.controlClause(false, s.Init, s.Cond, nil)
p.block(s.Body, 1)
if s.Else != nil {
p.print(blank, token.ELSE, blank)
switch s.Else.(type) {
case *ast.BlockStmt, *ast.IfStmt:
p.stmt(s.Else, nextIsRBrace)
default:
// This can only happen with an incorrectly
// constructed AST. Permit it but print so
// that it can be parsed without errors.
p.print(token.LBRACE, indent, formfeed)
p.stmt(s.Else, true)
p.print(unindent, formfeed, token.RBRACE)
}
}
case *ast.CaseClause:
if s.List != nil {
p.print(token.CASE, blank)
p.exprList(s.Pos(), s.List, 1, 0, s.Colon, false)
} else {
p.print(token.DEFAULT)
}
p.print(s.Colon, token.COLON)
p.stmtList(s.Body, 1, nextIsRBrace)
case *ast.SwitchStmt:
p.print(token.SWITCH)
p.controlClause(false, s.Init, s.Tag, nil)
p.block(s.Body, 0)
case *ast.TypeSwitchStmt:
p.print(token.SWITCH)
if s.Init != nil {
p.print(blank)
p.stmt(s.Init, false)
p.print(token.SEMICOLON)
}
p.print(blank)
p.stmt(s.Assign, false)
p.print(blank)
p.block(s.Body, 0)
case *ast.CommClause:
if s.Comm != nil {
p.print(token.CASE, blank)
p.stmt(s.Comm, false)
} else {
p.print(token.DEFAULT)
}
p.print(s.Colon, token.COLON)
p.stmtList(s.Body, 1, nextIsRBrace)
case *ast.SelectStmt:
p.print(token.SELECT, blank)
body := s.Body
if len(body.List) == 0 && !p.commentBefore(p.posFor(body.Rbrace)) {
// print empty select statement w/o comments on one line
p.print(body.Lbrace, token.LBRACE, body.Rbrace, token.RBRACE)
} else {
p.block(body, 0)
}
case *ast.ForStmt:
p.print(token.FOR)
p.controlClause(true, s.Init, s.Cond, s.Post)
p.block(s.Body, 1)
case *ast.RangeStmt:
p.print(token.FOR, blank)
if s.Key != nil {
p.expr(s.Key)
if s.Value != nil {
// use position of value following the comma as
// comma position for correct comment placement
p.print(s.Value.Pos(), token.COMMA, blank)
p.expr(s.Value)
}
p.print(blank, s.TokPos, s.Tok, blank)
}
p.print(token.RANGE, blank)
p.expr(stripParens(s.X))
p.print(blank)
p.block(s.Body, 1)
default:
panic("unreachable")
}
}
// ----------------------------------------------------------------------------
// Declarations
// The keepTypeColumn function determines if the type column of a series of
// consecutive const or var declarations must be kept, or if initialization
// values (V) can be placed in the type column (T) instead. The i'th entry
// in the result slice is true if the type column in spec[i] must be kept.
//
// For example, the declaration:
//
// const (
// foobar int = 42 // comment
// x = 7 // comment
// foo
// bar = 991
// )
//
// leads to the type/values matrix below. A run of value columns (V) can
// be moved into the type column if there is no type for any of the values
// in that column (we only move entire columns so that they align properly).
//
// matrix formatted result
// matrix
// T V -> T V -> true there is a T and so the type
// - V - V true column must be kept
// - - - - false
// - V V - false V is moved into T column
//
func keepTypeColumn(specs []ast.Spec) []bool {
m := make([]bool, len(specs))
populate := func(i, j int, keepType bool) {
if keepType {
for ; i < j; i++ {
m[i] = true
}
}
}
i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
var keepType bool
for i, s := range specs {
t := s.(*ast.ValueSpec)
if t.Values != nil {
if i0 < 0 {
// start of a run of ValueSpecs with non-nil Values
i0 = i
keepType = false
}
} else {
if i0 >= 0 {
// end of a run
populate(i0, i, keepType)
i0 = -1
}
}
if t.Type != nil {
keepType = true
}
}
if i0 >= 0 {
// end of a run
populate(i0, len(specs), keepType)
}
return m
}
func (p *printer) valueSpec(s *ast.ValueSpec, keepType bool) {
p.setComment(s.Doc)
p.identList(s.Names, false) // always present
extraTabs := 3
if s.Type != nil || keepType {
p.print(vtab)
extraTabs--
}
if s.Type != nil {
p.expr(s.Type)
}
if s.Values != nil {
p.print(vtab, token.ASSIGN, blank)
p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
extraTabs--
}
if s.Comment != nil {
for ; extraTabs > 0; extraTabs-- {
p.print(vtab)
}
p.setComment(s.Comment)
}
}
func sanitizeImportPath(lit *ast.BasicLit) *ast.BasicLit {
// Note: An unmodified AST generated by go/parser will already
// contain a backward- or double-quoted path string that does
// not contain any invalid characters, and most of the work
// here is not needed. However, a modified or generated AST
// may possibly contain non-canonical paths. Do the work in
// all cases since it's not too hard and not speed-critical.
// if we don't have a proper string, be conservative and return whatever we have
if lit.Kind != token.STRING {
return lit
}
s, err := strconv.Unquote(lit.Value)
if err != nil {
return lit
}
// if the string is an invalid path, return whatever we have
//
// spec: "Implementation restriction: A compiler may restrict
// ImportPaths to non-empty strings using only characters belonging
// to Unicode's L, M, N, P, and S general categories (the Graphic
// characters without spaces) and may also exclude the characters
// !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character
// U+FFFD."
if s == "" {
return lit
}
const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
for _, r := range s {
if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
return lit
}
}
// otherwise, return the double-quoted path
s = strconv.Quote(s)
if s == lit.Value {
return lit // nothing wrong with lit
}
return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: token.STRING, Value: s}
}
// The parameter n is the number of specs in the group. If doIndent is set,
// multi-line identifier lists in the spec are indented when the first
// linebreak is encountered.
//
func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
switch s := spec.(type) {
case *ast.ImportSpec:
p.setComment(s.Doc)
if s.Name != nil {
p.expr(s.Name)
p.print(blank)
}
p.expr(sanitizeImportPath(s.Path))
p.setComment(s.Comment)
p.print(s.EndPos)
case *ast.ValueSpec:
if n != 1 {
p.internalError("expected n = 1; got", n)
}
p.setComment(s.Doc)
p.identList(s.Names, doIndent) // always present
if s.Type != nil {
p.print(blank)
p.expr(s.Type)
}
if s.Values != nil {
p.print(blank, token.ASSIGN, blank)
p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
}
p.setComment(s.Comment)
case *ast.TypeSpec:
p.setComment(s.Doc)
p.expr(s.Name)
if n == 1 {
p.print(blank)
} else {
p.print(vtab)
}
if s.Assign.IsValid() {
p.print(token.ASSIGN, blank)
}
p.expr(s.Type)
p.setComment(s.Comment)
default:
panic("unreachable")
}
}
func (p *printer) genDecl(d *ast.GenDecl) {
p.setComment(d.Doc)
p.print(d.Pos(), d.Tok, blank)
if d.Lparen.IsValid() || len(d.Specs) > 1 {
// group of parenthesized declarations
p.print(d.Lparen, token.LPAREN)
if n := len(d.Specs); n > 0 {
p.print(indent, formfeed)
if n > 1 && (d.Tok == token.CONST || d.Tok == token.VAR) {
// two or more grouped const/var declarations:
// determine if the type column must be kept
keepType := keepTypeColumn(d.Specs)
var line int
for i, s := range d.Specs {
if i > 0 {
p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
}
p.recordLine(&line)
p.valueSpec(s.(*ast.ValueSpec), keepType[i])
}
} else {
var line int
for i, s := range d.Specs {
if i > 0 {
p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
}
p.recordLine(&line)
p.spec(s, n, false)
}
}
p.print(unindent, formfeed)
}
p.print(d.Rparen, token.RPAREN)
} else if len(d.Specs) > 0 {
// single declaration
p.spec(d.Specs[0], 1, true)
}
}
// nodeSize determines the size of n in chars after formatting.
// The result is <= maxSize if the node fits on one line with at
// most maxSize chars and the formatted output doesn't contain
// any control chars. Otherwise, the result is > maxSize.
//
func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
// nodeSize invokes the printer, which may invoke nodeSize
// recursively. For deep composite literal nests, this can
// lead to an exponential algorithm. Remember previous
// results to prune the recursion (was issue 1628).
if size, found := p.nodeSizes[n]; found {
return size
}
size = maxSize + 1 // assume n doesn't fit
p.nodeSizes[n] = size
// nodeSize computation must be independent of particular
// style so that we always get the same decision; print
// in RawFormat
cfg := Config{Mode: RawFormat}
var buf bytes.Buffer
if err := cfg.fprint(&buf, p.fset, n, p.nodeSizes); err != nil {
return
}
if buf.Len() <= maxSize {
for _, ch := range buf.Bytes() {
if ch < ' ' {
return
}
}
size = buf.Len() // n fits
p.nodeSizes[n] = size
}
return
}
// numLines returns the number of lines spanned by node n in the original source.
func (p *printer) numLines(n ast.Node) int {
if from := n.Pos(); from.IsValid() {
if to := n.End(); to.IsValid() {
return p.lineFor(to) - p.lineFor(from) + 1
}
}
return infinity
}
// bodySize is like nodeSize but it is specialized for *ast.BlockStmt's.
func (p *printer) bodySize(b *ast.BlockStmt, maxSize int) int {
pos1 := b.Pos()
pos2 := b.Rbrace
if pos1.IsValid() && pos2.IsValid() && p.lineFor(pos1) != p.lineFor(pos2) {
// opening and closing brace are on different lines - don't make it a one-liner
return maxSize + 1
}
if len(b.List) > 5 {
// too many statements - don't make it a one-liner
return maxSize + 1
}
// otherwise, estimate body size
bodySize := p.commentSizeBefore(p.posFor(pos2))
for i, s := range b.List {
if bodySize > maxSize {
break // no need to continue
}
if i > 0 {
bodySize += 2 // space for a semicolon and blank
}
bodySize += p.nodeSize(s, maxSize)
}
return bodySize
}
// funcBody prints a function body following a function header of given headerSize.
// If the header's and block's size are "small enough" and the block is "simple enough",
// the block is printed on the current line, without line breaks, spaced from the header
// by sep. Otherwise the block's opening "{" is printed on the current line, followed by
// lines for the block's statements and its closing "}".
//
func (p *printer) funcBody(headerSize int, sep whiteSpace, b *ast.BlockStmt) {
if b == nil {
return
}
// save/restore composite literal nesting level
defer func(level int) {
p.level = level
}(p.level)
p.level = 0
const maxSize = 100
if headerSize+p.bodySize(b, maxSize) <= maxSize {
p.print(sep, b.Lbrace, token.LBRACE)
if len(b.List) > 0 {
p.print(blank)
for i, s := range b.List {
if i > 0 {
p.print(token.SEMICOLON, blank)
}
p.stmt(s, i == len(b.List)-1)
}
p.print(blank)
}
p.print(noExtraLinebreak, b.Rbrace, token.RBRACE, noExtraLinebreak)
return
}
if sep != ignore {
p.print(blank) // always use blank
}
p.block(b, 1)
}
// distanceFrom returns the column difference between from and p.pos (the current
// estimated position) if both are on the same line; if they are on different lines
// (or unknown) the result is infinity.
func (p *printer) distanceFrom(from token.Pos) int {
if from.IsValid() && p.pos.IsValid() {
if f := p.posFor(from); f.Line == p.pos.Line {
return p.pos.Column - f.Column
}
}
return infinity
}
func (p *printer) funcDecl(d *ast.FuncDecl) {
p.setComment(d.Doc)
p.print(d.Pos(), token.FUNC, blank)
if d.Recv != nil {
p.parameters(d.Recv) // method: print receiver
p.print(blank)
}
p.expr(d.Name)
p.signature(d.Type.Params, d.Type.Results)
p.funcBody(p.distanceFrom(d.Pos()), vtab, d.Body)
}
func (p *printer) decl(decl ast.Decl) {
switch d := decl.(type) {
case *ast.BadDecl:
p.print(d.Pos(), "BadDecl")
case *ast.GenDecl:
p.genDecl(d)
case *ast.FuncDecl:
p.funcDecl(d)
default:
panic("unreachable")
}
}
// ----------------------------------------------------------------------------
// Files
func declToken(decl ast.Decl) (tok token.Token) {
tok = token.ILLEGAL
switch d := decl.(type) {
case *ast.GenDecl:
tok = d.Tok
case *ast.FuncDecl:
tok = token.FUNC
}
return
}
func (p *printer) declList(list []ast.Decl) {
tok := token.ILLEGAL
for _, d := range list {
prev := tok
tok = declToken(d)
// If the declaration token changed (e.g., from CONST to TYPE)
// or the next declaration has documentation associated with it,
// print an empty line between top-level declarations.
// (because p.linebreak is called with the position of d, which
// is past any documentation, the minimum requirement is satisfied
// even w/o the extra getDoc(d) nil-check - leave it in case the
// linebreak logic improves - there's already a TODO).
if len(p.output) > 0 {
// only print line break if we are not at the beginning of the output
// (i.e., we are not printing only a partial program)
min := 1
if prev != tok || getDoc(d) != nil {
min = 2
}
// start a new section if the next declaration is a function
// that spans multiple lines (see also issue #19544)
p.linebreak(p.lineFor(d.Pos()), min, ignore, tok == token.FUNC && p.numLines(d) > 1)
}
p.decl(d)
}
}
func (p *printer) file(src *ast.File) {
p.setComment(src.Doc)
p.print(src.Pos(), token.PACKAGE, blank)
p.expr(src.Name)
p.declList(src.Decls)
p.print(newline)
}
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