go/printer, gofmt: align comments in multi-line expression lists

- gofmt -w src misc
- improves several lists and fixes minor degradation introduced
  with the fix for issue 628
- removed some dead code (stringList)

R=rsc
CC=golang-dev
https://golang.org/cl/223058

src/pkg/go/printer/nodes.go

@@ -92,29 +92,24 @@ func (p *printer) identList(list []*ast.Ident, multiLine *bool) {
 }
 
 
-// Sets multiLine to true if the string list spans multiple lines.
-func (p *printer) stringList(list []*ast.BasicLit, multiLine *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
-	}
-	p.exprList(noPos, xlist, 1, plusSep, multiLine, noPos)
-}
-
-
 type exprListMode uint
 
 const (
 	blankStart exprListMode = 1 << iota // print a blank before a non-empty list
 	blankEnd                // print a blank after a non-empty list
-	plusSep                 // elements are separared by + operators
 	commaSep                // elements are separated by commas
 	commaTerm               // list is optionally terminated by a comma
 	noIndent                // no extra indentation in multi-line lists
 )
 
 
+// isOneLineExpr returns true if x is "small enough" to fit onto a single line.
+func (p *printer) isOneLineExpr(x ast.Expr) bool {
+	const maxSize = 60 // aproximate value, excluding space for comments
+	return p.nodeSize(x, maxSize) <= maxSize
+}
+
+
 // Print a list of expressions. If the list spans multiple
 // source lines, the original line breaks are respected between
 // expressions. Sets multiLine to true if the list spans multiple
@@ -141,9 +136,6 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, depth int, mode
 		// all list entries on a single line
 		for i, x := range list {
 			if i > 0 {
-				if mode&plusSep != 0 {
-					p.print(blank, token.ADD)
-				}
 				if mode&commaSep != 0 {
 					p.print(token.COMMA)
 				}
@@ -167,31 +159,42 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, depth int, mode
 		ws = indent
 	}
 
+	// the first linebreak is always a formfeed since this section must not
+	// depend on any previous formatting
 	if prev.IsValid() && prev.Line < line && p.linebreak(line, 1, 2, ws, true) {
 		ws = ignore
 		*multiLine = true
 	}
 
+	oneLiner := false // true if the previous expression fit on a single line
+	prevBreak := 0    // index of last expression that was followed by a linebreak
 	for i, x := range list {
 		prev := line
 		line = x.Pos().Line
 		if i > 0 {
-			if mode&plusSep != 0 {
-				p.print(blank, token.ADD)
-			}
 			if mode&commaSep != 0 {
 				p.print(token.COMMA)
 			}
 			if prev < line && prev > 0 && line > 0 {
-				if p.linebreak(line, 1, 2, ws, true) {
+				// lines are broken using newlines so comments remain aligned,
+				// but if an expression is not a "one-line" expression, or if
+				// multiple expressions are on the same line, the section is
+				// broken with a formfeed
+				if p.linebreak(line, 1, 2, ws, !oneLiner || prevBreak+1 < i) {
 					ws = ignore
 					*multiLine = true
+					prevBreak = i
 				}
 			} else {
 				p.print(blank)
 			}
 		}
 		p.expr0(x, depth, multiLine)
+		// determine if x satisfies the "one-liner" criteria
+		// TODO(gri): determine if the multiline information returned
+		//            from p.expr0 is precise enough so it could be
+		//            used instead
+		oneLiner = p.isOneLineExpr(x)
 	}
 
 	if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {

src/pkg/go/printer/printer.go

@@ -40,9 +40,9 @@ const (
 var (
 	esc       = []byte{tabwriter.Escape}
 	htab      = []byte{'\t'}
-	htabs     = [...]byte{'\t', '\t', '\t', '\t', '\t', '\t', '\t', '\t'}
+	htabs     = []byte("\t\t\t\t\t\t\t\t")
-	newlines  = [...]byte{'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'} // more than maxNewlines
+	newlines  = []byte("\n\n\n\n\n\n\n\n") // more than maxNewlines
-	formfeeds = [...]byte{'\f', '\f', '\f', '\f', '\f', '\f', '\f', '\f'} // more than maxNewlines
+	formfeeds = []byte("\f\f\f\f\f\f\f\f") // more than maxNewlines
 
 	esc_quot = []byte(""") // shorter than """
 	esc_apos = []byte("'") // shorter than "'"
@@ -147,7 +147,7 @@ func (p *printer) write(data []byte) {
 				// must not be discarded by the tabwriter
 				j := p.indent
 				for ; j > len(htabs); j -= len(htabs) {
-					p.write0(&htabs)
+					p.write0(htabs)
 				}
 				p.write0(htabs[0:j])
 
@@ -526,7 +526,7 @@ func stripCommonPrefix(lines [][]byte) {
 	// with the opening /*, otherwise align the text with the other
 	// lines.
 	last := lines[len(lines)-1]
-	closing := []byte{'*', '/'}
+	closing := []byte("*/")
 	i := bytes.Index(last, closing)
 	if isBlank(last[0:i]) {
 		// last line only contains closing */

src/pkg/go/printer/testdata/expressions.golden

@@ -337,6 +337,21 @@ func _() {
 }
 
 
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,		// yellow
+	draw.Cyan,		// cyan
+	draw.Green,		// lime green
+	draw.GreyBlue,		// slate
+	draw.Red,		/* red */
+	draw.GreyGreen,		/* olive green */
+	draw.Blue,		/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+
 func same(t, u *Time) bool {
 	// respect source lines in multi-line expressions
 	return t.Year == u.Year &&

src/pkg/go/printer/testdata/expressions.input

@@ -341,6 +341,21 @@ func _() {
 }
 
 
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow, // yellow
+	draw.Cyan, // cyan
+	draw.Green, // lime green
+	draw.GreyBlue, // slate
+	draw.Red, /* red */
+	draw.GreyGreen, /* olive green */
+	draw.Blue, /* blue */
+	draw.Color(0xFF55AAFF), /* pink */
+	draw.Color(0xFFAAFFFF), /* lavender */
+	draw.Color(0xBB005DFF), /* maroon */
+}
+
+
 func same(t, u *Time) bool {
 	// respect source lines in multi-line expressions
 	return t.Year == u.Year &&

src/pkg/go/printer/testdata/expressions.raw

@@ -337,6 +337,21 @@ func _() {
 }
 
 
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,	// yellow
+	draw.Cyan,	// cyan
+	draw.Green,	// lime green
+	draw.GreyBlue,	// slate
+	draw.Red,	/* red */
+	draw.GreyGreen,	/* olive green */
+	draw.Blue,	/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+
 func same(t, u *Time) bool {
 	// respect source lines in multi-line expressions
 	return t.Year == u.Year &&