go/printer: make //line formatting idempotent

Fixes "test.sh" (long test) in src/cmd/gofmt.

R=gri
CC=golang-dev
https://golang.org/cl/5307081

diff --git a/src/pkg/go/printer/printer.go b/src/pkg/go/printer/printer.go
index aba7d93a64bbff874bb94bd87d95d354aa48bdcc..6104c326c665ea7c0cb12419b3521e4c44c5e40f 100644 (file)
--- a/src/pkg/go/printer/printer.go
+++ b/src/pkg/go/printer/printer.go
@@ -13,6 +13,8 @@ import (
        "io"
        "os"
        "path/filepath"
+       "strconv"
+       "strings"
        "text/tabwriter"
 )
 
@@ -244,6 +246,8 @@ func (p *printer) writeItem(pos token.Position, data string) {
        p.last = p.pos
 }
 
+const linePrefix = "//line "
+
 // writeCommentPrefix writes the whitespace before a comment.
 // If there is any pending whitespace, it consumes as much of
 // it as is likely to help position the comment nicely.
@@ -252,7 +256,7 @@ func (p *printer) writeItem(pos token.Position, data string) {
 // a group of comments (or nil), and isKeyword indicates if the
 // next item is a keyword.
 //
-func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment, isKeyword bool) {
+func (p *printer) writeCommentPrefix(pos, next token.Position, prev, comment *ast.Comment, isKeyword bool) {
        if p.written == 0 {
                // the comment is the first item to be printed - don't write any whitespace
                return
@@ -337,6 +341,13 @@ func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment
                        }
                        p.writeWhitespace(j)
                }
+
+               // turn off indent if we're about to print a line directive.
+               indent := p.indent
+               if strings.HasPrefix(comment.Text, linePrefix) {
+                       p.indent = 0
+               }
+
                // use formfeeds to break columns before a comment;
                // this is analogous to using formfeeds to separate
                // individual lines of /*-style comments - but make
@@ -347,6 +358,7 @@ func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment
                        n = 1
                }
                p.writeNewlines(n, true)
+               p.indent = indent
        }
 }
 
@@ -526,6 +538,26 @@ func stripCommonPrefix(lines [][]byte) {
 func (p *printer) writeComment(comment *ast.Comment) {
        text := comment.Text
 
+       if strings.HasPrefix(text, linePrefix) {
+               pos := strings.TrimSpace(text[len(linePrefix):])
+               i := strings.LastIndex(pos, ":")
+               if i >= 0 {
+                       // The line directive we are about to print changed
+                       // the Filename and Line number used by go/token
+                       // as it was reading the input originally.
+                       // In order to match the original input, we have to
+                       // update our own idea of the file and line number
+                       // accordingly, after printing the directive.
+                       file := pos[:i]
+                       line, _ := strconv.Atoi(string(pos[i+1:]))
+                       defer func() {
+                               p.pos.Filename = string(file)
+                               p.pos.Line = line
+                               p.pos.Column = 1
+                       }()
+               }
+       }
+
        // shortcut common case of //-style comments
        if text[1] == '/' {
                p.writeItem(p.fset.Position(comment.Pos()), p.escape(text))
@@ -599,7 +631,7 @@ func (p *printer) intersperseComments(next token.Position, tok token.Token) (dro
        var last *ast.Comment
        for ; p.commentBefore(next); p.cindex++ {
                for _, c := range p.comments[p.cindex].List {
-                       p.writeCommentPrefix(p.fset.Position(c.Pos()), next, last, tok.IsKeyword())
+                       p.writeCommentPrefix(p.fset.Position(c.Pos()), next, last, c, tok.IsKeyword())
                        p.writeComment(c)
                        last = c
                }