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

11 files changed, 115 insertions, 67 deletions

diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index fc2da37c17..d8f35e128a 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -280,14 +280,14 @@ func (p *Prog) gccDebug(stdin []byte) (*dwarf.Data, string) {
 	base := []string{
 		"gcc",
 		machine,
-		"-Wall", // many warnings
-		"-Werror", // warnings are errors
-		"-o" + tmp, // write object to tmp
-		"-gdwarf-2", // generate DWARF v2 debugging symbols
+		"-Wall",                             // many warnings
+		"-Werror",                           // warnings are errors
+		"-o" + tmp,                          // write object to tmp
+		"-gdwarf-2",                         // generate DWARF v2 debugging symbols
 		"-fno-eliminate-unused-debug-types", // gets rid of e.g. untyped enum otherwise
-		"-c", // do not link
-		"-xc", // input language is C
-		"-", // read input from standard input
+		"-c",                                // do not link
+		"-xc",                               // input language is C
+		"-",                                 // read input from standard input
 	}
 	_, stderr, ok := run(stdin, concat(base, p.GccOptions))
 	if !ok {
diff --git a/src/cmd/godoc/godoc.go b/src/cmd/godoc/godoc.go
index 29792d58f7..c6438245eb 100644
--- a/src/cmd/godoc/godoc.go
+++ b/src/cmd/godoc/godoc.go
@@ -935,7 +935,7 @@ func redirect(c *http.Conn, r *http.Request) (redirected bool) {
 // textExt[x] is true if the extension x indicates a text file, and false otherwise.
 var textExt = map[string]bool{
 	".css": false, // must be served raw
-	".js": false, // must be served raw
+	".js": false,  // must be served raw
 }
 
 
diff --git a/src/pkg/exp/4s/xs.go b/src/pkg/exp/4s/xs.go
index d8f0ce2a11..c5493e719e 100644
--- a/src/pkg/exp/4s/xs.go
+++ b/src/pkg/exp/4s/xs.go
@@ -145,13 +145,13 @@ var txbits = [NCOL][32]byte{
 }
 
 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.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 */
diff --git a/src/pkg/go/printer/nodes.go b/src/pkg/go/printer/nodes.go
index 89b44f598c..b9b8900169 100644
--- a/src/pkg/go/printer/nodes.go
+++ b/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 {
diff --git a/src/pkg/go/printer/printer.go b/src/pkg/go/printer/printer.go
index 44bc3bb0ba..65979fda7f 100644
--- a/src/pkg/go/printer/printer.go
+++ b/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'}
-	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
+	htabs     = []byte("\t\t\t\t\t\t\t\t")
+	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
 
 	esc_quot = []byte("&#34;") // shorter than "&quot;"
 	esc_apos = []byte("&#39;") // shorter than "&apos;"
@@ -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 */
diff --git a/src/pkg/go/printer/testdata/expressions.golden b/src/pkg/go/printer/testdata/expressions.golden
index b688c9bc02..6626c546b7 100644
--- a/src/pkg/go/printer/testdata/expressions.golden
+++ b/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 &&
diff --git a/src/pkg/go/printer/testdata/expressions.input b/src/pkg/go/printer/testdata/expressions.input
index b05c51ef8a..0b67a763ef 100644
--- a/src/pkg/go/printer/testdata/expressions.input
+++ b/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 &&
diff --git a/src/pkg/go/printer/testdata/expressions.raw b/src/pkg/go/printer/testdata/expressions.raw
index 10964a45e9..406fbf695a 100644
--- a/src/pkg/go/printer/testdata/expressions.raw
+++ b/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 &&
diff --git a/src/pkg/go/scanner/scanner_test.go b/src/pkg/go/scanner/scanner_test.go
index fe342bcdf2..ad54dfd1fa 100644
--- a/src/pkg/go/scanner/scanner_test.go
+++ b/src/pkg/go/scanner/scanner_test.go
@@ -431,8 +431,8 @@ var segments = []seg{
 	seg{"\n//line File2.go:200\n  line200", "File2.go", 200},
 	seg{"\n//line :1\n  line1", "", 1},
 	seg{"\n//line foo:42\n  line42", "foo", 42},
-	seg{"\n //line foo:42\n  line44", "foo", 44}, // bad line comment, ignored
-	seg{"\n//line foo 42\n  line46", "foo", 46}, // bad line comment, ignored
+	seg{"\n //line foo:42\n  line44", "foo", 44},           // bad line comment, ignored
+	seg{"\n//line foo 42\n  line46", "foo", 46},            // bad line comment, ignored
 	seg{"\n//line foo:42 extra text\n  line48", "foo", 48}, // bad line comment, ignored
 	seg{"\n//line foo:42\n  line42", "foo", 42},
 	seg{"\n//line foo:42\n  line42", "foo", 42},
diff --git a/src/pkg/http/response_test.go b/src/pkg/http/response_test.go
index 51126570db..6024a62719 100644
--- a/src/pkg/http/response_test.go
+++ b/src/pkg/http/response_test.go
@@ -60,7 +60,7 @@ var respTests = []respTest{
 			ProtoMinor: 0,
 			RequestMethod: "GET",
 			Header: map[string]string{
-				"Connection": "close", // TODO(rsc): Delete?
+				"Connection": "close",  // TODO(rsc): Delete?
 				"Content-Length": "10", // TODO(rsc): Delete?
 			},
 			Close: true,
diff --git a/src/pkg/strconv/decimal.go b/src/pkg/strconv/decimal.go
index 02c6618cb8..3a7ebf926b 100644
--- a/src/pkg/strconv/decimal.go
+++ b/src/pkg/strconv/decimal.go
@@ -195,31 +195,31 @@ var leftcheats = []leftCheat{
 		}'
 	*/
 	leftCheat{0, ""},
-	leftCheat{1, "5"}, // * 2
-	leftCheat{1, "25"}, // * 4
-	leftCheat{1, "125"}, // * 8
-	leftCheat{2, "625"}, // * 16
-	leftCheat{2, "3125"}, // * 32
-	leftCheat{2, "15625"}, // * 64
-	leftCheat{3, "78125"}, // * 128
-	leftCheat{3, "390625"}, // * 256
-	leftCheat{3, "1953125"}, // * 512
-	leftCheat{4, "9765625"}, // * 1024
-	leftCheat{4, "48828125"}, // * 2048
-	leftCheat{4, "244140625"}, // * 4096
-	leftCheat{4, "1220703125"}, // * 8192
-	leftCheat{5, "6103515625"}, // * 16384
-	leftCheat{5, "30517578125"}, // * 32768
-	leftCheat{5, "152587890625"}, // * 65536
-	leftCheat{6, "762939453125"}, // * 131072
-	leftCheat{6, "3814697265625"}, // * 262144
-	leftCheat{6, "19073486328125"}, // * 524288
-	leftCheat{7, "95367431640625"}, // * 1048576
-	leftCheat{7, "476837158203125"}, // * 2097152
-	leftCheat{7, "2384185791015625"}, // * 4194304
-	leftCheat{7, "11920928955078125"}, // * 8388608
-	leftCheat{8, "59604644775390625"}, // * 16777216
-	leftCheat{8, "298023223876953125"}, // * 33554432
+	leftCheat{1, "5"},                   // * 2
+	leftCheat{1, "25"},                  // * 4
+	leftCheat{1, "125"},                 // * 8
+	leftCheat{2, "625"},                 // * 16
+	leftCheat{2, "3125"},                // * 32
+	leftCheat{2, "15625"},               // * 64
+	leftCheat{3, "78125"},               // * 128
+	leftCheat{3, "390625"},              // * 256
+	leftCheat{3, "1953125"},             // * 512
+	leftCheat{4, "9765625"},             // * 1024
+	leftCheat{4, "48828125"},            // * 2048
+	leftCheat{4, "244140625"},           // * 4096
+	leftCheat{4, "1220703125"},          // * 8192
+	leftCheat{5, "6103515625"},          // * 16384
+	leftCheat{5, "30517578125"},         // * 32768
+	leftCheat{5, "152587890625"},        // * 65536
+	leftCheat{6, "762939453125"},        // * 131072
+	leftCheat{6, "3814697265625"},       // * 262144
+	leftCheat{6, "19073486328125"},      // * 524288
+	leftCheat{7, "95367431640625"},      // * 1048576
+	leftCheat{7, "476837158203125"},     // * 2097152
+	leftCheat{7, "2384185791015625"},    // * 4194304
+	leftCheat{7, "11920928955078125"},   // * 8388608
+	leftCheat{8, "59604644775390625"},   // * 16777216
+	leftCheat{8, "298023223876953125"},  // * 33554432
 	leftCheat{8, "1490116119384765625"}, // * 67108864
 	leftCheat{9, "7450580596923828125"}, // * 134217728
 }