gofmt: fix some linebreak issues

- don't lose empty lines after labels
- canonicalize number of line breaks
- gofmt src misc, fixes a couple of irregular breaks

R=rsc
CC=golang-dev
https://golang.org/cl/1843044

src/pkg/compress/flate/huffman_code.go

@@ -270,7 +270,6 @@ func (h *huffmanEncoder) bitCounts(list []literalNode, maxBits int32) []int32 {
 		}
 	}
 
-
 	// Somethings is wrong if at the end, the top level is null or hasn't used
 	// all of the leaves.
 	if top.lastChain.leafCount != n {

src/pkg/compress/flate/inflate.go

@@ -102,7 +102,6 @@ func (h *huffmanDecoder) init(bits []int) bool {
 	h.min = min
 	h.max = max
 
-
 	// For each code range, compute
 	// nextcode (first code of that length),
 	// limit (last code of that length), and

src/pkg/go/doc/comment.go

@@ -224,7 +224,6 @@ func emphasize(w io.Writer, line []byte, words map[string]string, nice bool) {
 			italics = false // don't italicize URLs
 		}
 
-
 		// write match
 		if len(url) > 0 {
 			w.Write(html_a)

src/pkg/go/printer/nodes.go

@@ -28,32 +28,30 @@ import (
 // ----------------------------------------------------------------------------
 // Common AST nodes.
 
-// Print as many newlines as necessary (but at least min and and at most
-// max 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.
+// 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): Reconsider signature (provide position instead of line)
+// TODO(gri): linebreak may add too many lines if the next statement at "line"
+//            is preceeded 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, max int, ws whiteSpace, newSection bool) (printedBreak bool) {
-	n := line - p.pos.Line
-	switch {
-	case n < min:
-		n = min
-	case n > max:
-		n = max
-	}
-
+func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (printedBreak bool) {
+	n := p.nlines(line-p.pos.Line, min)
 	if n > 0 {
 		p.print(ws)
 		if newSection {
 			p.print(formfeed)
 			n--
-			printedBreak = true
 		}
-	}
-	for ; n > 0; n-- {
-		p.print(newline)
+		for ; n > 0; n-- {
+			p.print(newline)
+		}
 		printedBreak = true
 	}
 	return
@@ -190,7 +188,7 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, depth int, mode
 		// lines for them.
 		linebreakMin = 0
 	}
-	if prev.IsValid() && prev.Line < line && p.linebreak(line, linebreakMin, 2, ws, true) {
+	if prev.IsValid() && prev.Line < line && p.linebreak(line, linebreakMin, ws, true) {
 		ws = ignore
 		*multiLine = true
 		prevBreak = 0
@@ -252,7 +250,7 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, depth int, mode
 				// unless forceFF is set or there are multiple expressions on
 				// the same line in which case formfeed is used
 				// broken with a formfeed
-				if p.linebreak(line, linebreakMin, 2, ws, useFF || prevBreak+1 < i) {
+				if p.linebreak(line, linebreakMin, ws, useFF || prevBreak+1 < i) {
 					ws = ignore
 					*multiLine = true
 					prevBreak = i
@@ -371,6 +369,11 @@ func (p *printer) setLineComment(text string) {
 
 
 func (p *printer) fieldList(fields *ast.FieldList, isIncomplete bool, ctxt exprContext) {
+	p.nesting++
+	defer func() {
+		p.nesting--
+	}()
+
 	lbrace := fields.Opening
 	list := fields.List
 	rbrace := fields.Closing
@@ -413,7 +416,7 @@ func (p *printer) fieldList(fields *ast.FieldList, isIncomplete bool, ctxt exprC
 		var ml bool
 		for i, f := range list {
 			if i > 0 {
-				p.linebreak(f.Pos().Line, 1, 2, ignore, ml)
+				p.linebreak(f.Pos().Line, 1, ignore, ml)
 			}
 			ml = false
 			extraTabs := 0
@@ -457,7 +460,7 @@ func (p *printer) fieldList(fields *ast.FieldList, isIncomplete bool, ctxt exprC
 		var ml bool
 		for i, f := range list {
 			if i > 0 {
-				p.linebreak(f.Pos().Line, 1, 2, ignore, ml)
+				p.linebreak(f.Pos().Line, 1, ignore, ml)
 			}
 			ml = false
 			p.setComment(f.Doc)
@@ -648,7 +651,7 @@ func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int, multiL
 	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, 2, ws, true) {
+		if p.linebreak(yline, 1, ws, true) {
 			ws = ignore
 			*multiLine = true
 			printBlank = false // no blank after line break
@@ -917,8 +920,6 @@ func (p *printer) expr(x ast.Expr, multiLine *bool) {
 // ----------------------------------------------------------------------------
 // Statements
 
-const maxStmtNewlines = 2 // maximum number of newlines between 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.
@@ -931,7 +932,7 @@ func (p *printer) stmtList(list []ast.Stmt, _indent int, nextIsRBrace bool) {
 	for i, s := range list {
 		// _indent == 0 only for lists of switch/select case clauses;
 		// in those cases each clause is a new section
-		p.linebreak(s.Pos().Line, 1, maxStmtNewlines, ignore, i == 0 || _indent == 0 || multiLine)
+		p.linebreak(s.Pos().Line, 1, ignore, i == 0 || _indent == 0 || multiLine)
 		multiLine = false
 		p.stmt(s, nextIsRBrace && i == len(list)-1, &multiLine)
 	}
@@ -945,7 +946,7 @@ func (p *printer) stmtList(list []ast.Stmt, _indent int, nextIsRBrace bool) {
 func (p *printer) block(s *ast.BlockStmt, indent int) {
 	p.print(s.Pos(), token.LBRACE)
 	p.stmtList(s.List, indent, true)
-	p.linebreak(s.Rbrace.Line, 1, maxStmtNewlines, ignore, true)
+	p.linebreak(s.Rbrace.Line, 1, ignore, true)
 	p.print(s.Rbrace, token.RBRACE)
 }
 
@@ -1039,7 +1040,7 @@ func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool, multiLine *bool) {
 				break
 			}
 		} else {
-			p.print(newline)
+			p.linebreak(s.Stmt.Pos().Line, 1, ignore, true)
 		}
 		p.stmt(s.Stmt, nextIsRBrace, multiLine)
 
@@ -1271,7 +1272,7 @@ func (p *printer) genDecl(d *ast.GenDecl, multiLine *bool) {
 			var ml bool
 			for i, s := range d.Specs {
 				if i > 0 {
-					p.linebreak(s.Pos().Line, 1, 2, ignore, ml)
+					p.linebreak(s.Pos().Line, 1, ignore, ml)
 				}
 				ml = false
 				p.spec(s, len(d.Specs), false, &ml)
@@ -1345,6 +1346,11 @@ func (p *printer) funcBody(b *ast.BlockStmt, headerSize int, isLit bool, multiLi
 		return
 	}
 
+	p.nesting++
+	defer func() {
+		p.nesting--
+	}()
+
 	if p.isOneLineFunc(b, headerSize) {
 		sep := vtab
 		if isLit {
@@ -1414,8 +1420,6 @@ func (p *printer) decl(decl ast.Decl, multiLine *bool) {
 // ----------------------------------------------------------------------------
 // Files
 
-const maxDeclNewlines = 3 // maximum number of newlines between declarations
-
 func declToken(decl ast.Decl) (tok token.Token) {
 	tok = token.ILLEGAL
 	switch d := decl.(type) {
@@ -1444,7 +1448,7 @@ func (p *printer) file(src *ast.File) {
 			if prev != tok {
 				min = 2
 			}
-			p.linebreak(d.Pos().Line, min, maxDeclNewlines, ignore, false)
+			p.linebreak(d.Pos().Line, min, ignore, false)
 			p.decl(d, ignoreMultiLine)
 		}
 	}

src/pkg/go/printer/printer.go

@@ -18,10 +18,7 @@ import (
 )
 
 
-const (
-	debug       = false // enable for debugging
-	maxNewlines = 3     // maximum vertical white space
-)
+const debug = false // enable for debugging
 
 
 type whiteSpace int
@@ -41,8 +38,8 @@ 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
+	newlines  = []byte("\n\n\n\n\n\n\n\n") // more than the max determined by nlines
+	formfeeds = []byte("\f\f\f\f\f\f\f\f") // more than the max determined by nlines
 
 	esc_quot = []byte(""") // shorter than """
 	esc_apos = []byte("'") // shorter than "'"
@@ -68,6 +65,7 @@ type printer struct {
 	errors chan os.Error
 
 	// Current state
+	nesting int  // nesting level (0: top-level (package scope), >0: functions/decls.)
 	written int  // number of bytes written
 	indent  int  // current indentation
 	escape  bool // true if in escape sequence
@@ -112,6 +110,25 @@ func (p *printer) internalError(msg ...interface{}) {
 }
 
 
+// nlines returns the adjusted number of linebreaks given the desired number
+// of breaks n such that min <= result <= max where max depends on the current
+// nesting level.
+//
+func (p *printer) nlines(n, min int) int {
+	if n < min {
+		return min
+	}
+	max := 3 // max. number of newlines at the top level (p.nesting == 0)
+	if p.nesting > 0 {
+		max = 2 // max. number of newlines everywhere else
+	}
+	if n > max {
+		return max
+	}
+	return n
+}
+
+
 // write0 writes raw (uninterpreted) data to p.output and handles errors.
 // write0 does not indent after newlines, and does not HTML-escape or update p.pos.
 //
@@ -207,9 +224,7 @@ func (p *printer) write(data []byte) {
 
 func (p *printer) writeNewlines(n int, useFF bool) {
 	if n > 0 {
-		if n > maxNewlines {
-			n = maxNewlines
-		}
+		n = p.nlines(n, 0)
 		if useFF {
 			p.write(formfeeds[0:n])
 		} else {
@@ -292,8 +307,8 @@ func (p *printer) writeCommentPrefix(pos, next token.Position, isFirst, isKeywor
 	}
 
 	if pos.IsValid() && pos.Filename != p.last.Filename {
-		// comment in a different file - separate with newlines
-		p.writeNewlines(maxNewlines, true)
+		// comment in a different file - separate with newlines (writeNewlines will limit the number)
+		p.writeNewlines(10, true)
 		return
 	}
 
@@ -1004,9 +1019,11 @@ func (cfg *Config) Fprint(output io.Writer, node interface{}) (int, os.Error) {
 	go func() {
 		switch n := node.(type) {
 		case ast.Expr:
+			p.nesting = 1
 			p.useNodeComments = true
 			p.expr(n, ignoreMultiLine)
 		case ast.Stmt:
+			p.nesting = 1
 			p.useNodeComments = true
 			// A labeled statement will un-indent to position the
 			// label. Set indent to 1 so we don't get indent "underflow".
@@ -1015,12 +1032,15 @@ func (cfg *Config) Fprint(output io.Writer, node interface{}) (int, os.Error) {
 			}
 			p.stmt(n, false, ignoreMultiLine)
 		case ast.Decl:
+			p.nesting = 1
 			p.useNodeComments = true
 			p.decl(n, ignoreMultiLine)
 		case ast.Spec:
+			p.nesting = 1
 			p.useNodeComments = true
 			p.spec(n, 1, false, ignoreMultiLine)
 		case *ast.File:
+			p.nesting = 0
 			p.comments = n.Comments
 			p.useNodeComments = n.Comments == nil
 			p.file(n)

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

@@ -227,7 +227,8 @@ func _() {
 	var x = 1
 
 	// Each use(x) call below should have at most one empty line before and after.
-
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
 
 
 	use(x)
@@ -336,3 +337,49 @@ AnOverlongLabel:
 L:
 	_ = 0
 }
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}

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

@@ -164,6 +164,8 @@ func _() {
 	var x = 1
 
 	// Each use(x) call below should have at most one empty line before and after.
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
 
 
 
@@ -266,3 +268,54 @@ AnOverlongLabel:
 
 L:	_ = 0
 }
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+
+
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}

src/pkg/nntp/nntp_test.go

@@ -154,7 +154,6 @@ Body.
 		t.Fatal("newnews should work: " + err.String())
 	}
 
-
 	// NewGroups
 	if _, err = conn.NewGroups(tt); err != nil {
 		t.Fatal("newgroups shouldn't error " + err.String())