libgo: Update to Go 1.3 release.

[official-gcc.git] / libgo / go / go / printer / nodes.go

// 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"
        "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 true if any
// line break was printed; returns false otherwise.
//
// 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) (printedBreak bool) {
        n := nlimit(line - p.pos.Line)
        if n < min {
                n = min
        }
        if n > 0 {
                p.print(ws)
                if newSection {
                        p.print(formfeed)
                        n--
                }
                for ; n > 0; n-- {
                        p.print(newline)
                }
                printedBreak = true
        }
        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)
}

// 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) {
        if len(list) == 0 {
                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)
                }
                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) {
                ws = ignore
                prevBreak = 0
        }

        // initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
        size := 0

        // print all list elements
        for i, x := range list {
                prevLine := line
                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
                // the ratio between the key sizes does not exceed a
                // threshold, align columns and do not use formfeed
                if prevSize > 0 && size > 0 {
                        const smallSize = 20
                        if prevSize <= smallSize && size <= smallSize {
                                useFF = false
                        } else {
                                const r = 4 // threshold
                                ratio := float64(size) / float64(prevSize)
                                useFF = ratio <= 1.0/r || r <= ratio
                        }
                }

                if i > 0 {
                        needsLinebreak := prevLine < line && prevLine > 0 && line > 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 forceFF is set or there are multiple expressions on
                                // the same line in which case formfeed is used
                                if p.linebreak(line, 0, ws, useFF || prevBreak+1 < i) {
                                        ws = ignore
                                        prevBreak = i
                                        needsBlank = false // we got a line break instead
                                }
                        }
                        if needsBlank {
                                p.print(blank)
                        }
                }

                if isPair && size > 0 && len(list) > 1 {
                        // we have a key:value expression that fits onto one line and
                        // is in a list with more then one entry: use a column for the
                        // key such that consecutive entries can align if possible
                        p.expr(pair.Key)
                        p.print(pair.Colon, token.COLON, vtab)
                        p.expr(pair.Value)
                } else {
                        p.expr0(x, depth)
                }
        }

        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 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 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) {
                                // 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 isStruct && p.isOneLineFieldList(list) { // for now ignore interfaces
                        // small enough - print on one line
                        // (don't use identList and ignore source line breaks)
                        p.print(lbrace, token.LBRACE, blank)
                        f := list[0]
                        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)
                        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("// contains filtered or unexported fields")
                }

        } 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) {
                        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.adjBlock(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, reduceDepth(depth)) // parentheses undo one level of 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.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, unindent)
                } else {
                        p.print(x.Sel.Pos(), x.Sel)
                }

        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)
                }
                for i, y := range indices {
                        if i > 0 {
                                // blanks around ":" if both sides exist and either side is a binary expression
                                // TODO(gri) once we have committed a variant of a[i:j:k] we may want to fine-
                                //           tune the formatting here
                                x := indices[i-1]
                                if depth <= 1 && x != nil && y != nil && (isBinary(x) || isBinary(y)) {
                                        p.print(blank, token.COLON, blank)
                                } else {
                                        p.print(token.COLON)
                                }
                        }
                        if y != nil {
                                p.expr0(y, depth+1)
                        }
                }
                p.print(x.Rbrack, token.RBRACK)

        case *ast.CallExpr:
                if len(x.Args) > 1 {
                        depth++
                }
                if _, ok := x.Fun.(*ast.FuncType); ok {
                        // conversions to literal function types require parentheses around the type
                        p.print(token.LPAREN)
                        p.expr1(x.Fun, token.HighestPrec, depth)
                        p.print(token.RPAREN)
                } else {
                        p.expr1(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)
                        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)
                }
                p.print(x.Rparen, token.RPAREN)

        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.print(x.Lbrace, token.LBRACE)
                p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace)
                // 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
                }
                p.print(mode, x.Rbrace, token.RBRACE, mode)

        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")
        }

        return
}

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 returns true if 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)
                p.print(blank, s.TokPos, s.Tok, blank)
                p.exprList(s.TokPos, s.Rhs, depth, 0, token.NoPos)

        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)
                                p.print(unindent)
                        } else {
                                p.exprList(s.Pos(), s.Results, 1, 0, token.NoPos)
                        }
                }

        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:
                                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)
                } 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)
                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, token.RANGE, blank)
                p.expr(stripParens(s.X))
                p.print(blank)
                p.block(s.Body, 1)

        default:
                panic("unreachable")
        }

        return
}

// ----------------------------------------------------------------------------
// 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)
                extraTabs--
        }
        if s.Comment != nil {
                for ; extraTabs > 0; extraTabs-- {
                        p.print(vtab)
                }
                p.setComment(s.Comment)
        }
}

// 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(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)
                }
                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)
                }
                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() {
                // 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 {
                // 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
}

// 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
}

// adjBlock prints an "adjacent" block (e.g., a for-loop or function body) following
// a header (e.g., a for-loop control clause or function signature) 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) adjBlock(headerSize int, sep whiteSpace, b *ast.BlockStmt) {
        if b == nil {
                return
        }

        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.adjBlock(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
                        }
                        p.linebreak(p.lineFor(d.Pos()), min, ignore, false)
                }
                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)
}