go/printer, gofmt: respect line breaks in signatures

No changes when applying gofmt to src, misc.

Fixes #2597.

R=r
CC=golang-dev
https://golang.org/cl/5564056

src/pkg/go/printer/nodes.go

@@ -272,23 +272,32 @@ func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exp
 func (p *printer) parameters(fields *ast.FieldList, multiLine *bool) {
 	p.print(fields.Opening, token.LPAREN)
 	if len(fields.List) > 0 {
+		prevLine := p.fset.Position(fields.Opening).Line
 		ws := indent
-		var prevLine, line int
 		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
+			var parLineEnd = p.fset.Position(par.Type.Pos()).Line
+			if len(par.Names) > 0 {
+				parLineBeg = p.fset.Position(par.Names[0].Pos()).Line
+			} else {
+				parLineBeg = parLineEnd
+			}
+			// separating "," if needed
 			if i > 0 {
 				p.print(token.COMMA)
-				if len(par.Names) > 0 {
-					line = p.fset.Position(par.Names[0].Pos()).Line
-				} else {
-					line = p.fset.Position(par.Type.Pos()).Line
 			}
-				if 0 < prevLine && prevLine < line && p.linebreak(line, 0, ws, true) {
+			// separator if needed (linebreak or blank)
+			if 0 < prevLine && prevLine < parLineBeg && p.linebreak(parLineBeg, 0, ws, true) {
+				// break line if the opening "(" or previous parameter ended on a different line
 				ws = ignore
 				*multiLine = true
-				} else {
+			} 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
@@ -299,11 +308,18 @@ func (p *printer) parameters(fields *ast.FieldList, multiLine *bool) {
 				p.identList(par.Names, ws == indent, multiLine)
 				p.print(blank)
 			}
+			// parameter type
 			p.expr(par.Type, multiLine)
-			prevLine = p.fset.Position(par.Type.Pos()).Line
+			prevLine = parLineEnd
+		}
+		// if the closing ")" is on a separate line from the last parameter,
+		// print an additional "," and line break
+		if closing := p.fset.Position(fields.Closing).Line; 0 < prevLine && prevLine < closing {
+			p.print(",")
+			p.linebreak(closing, 0, ignore, true)
 		}
-		if ws == ignore {
 		// unindent if we indented
+		if ws == ignore {
 			p.print(unindent)
 		}
 	}

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

@@ -773,30 +773,39 @@ func ManageStatus(in <-chan *Status, req <-chan Request,
 	TargetHistorySize int) {
 }
 
-func MultiLineSignature0(a, b, c int) {
+func MultiLineSignature0(
+	a, b, c int,
+) {
 }
 
-func MultiLineSignature1(a, b, c int,
+func MultiLineSignature1(
-	u, v, w float) {
+	a, b, c int,
+	u, v, w float,
+) {
 }
 
-func MultiLineSignature2(a, b,
+func MultiLineSignature2(
-	c int) {
+	a, b,
+	c int,
+) {
 }
 
-func MultiLineSignature3(a, b,
+func MultiLineSignature3(
+	a, b,
 	c int, u, v,
 	w float,
 	x ...int) {
 }
 
-func MultiLineSignature4(a, b, c int,
+func MultiLineSignature4(
+	a, b, c int,
 	u, v,
 	w float,
 	x ...int) {
 }
 
-func MultiLineSignature5(a, b, c int,
+func MultiLineSignature5(
+	a, b, c int,
 	u, v, w float,
 	p, q,
 	r string,
@@ -805,25 +814,34 @@ func MultiLineSignature5(a, b, c int,
 
 // make sure it also works for methods in interfaces
 type _ interface {
-	MultiLineSignature0(a, b, c int)
+	MultiLineSignature0(
+		a, b, c int,
+	)
 
-	MultiLineSignature1(a, b, c int,
+	MultiLineSignature1(
-		u, v, w float)
+		a, b, c int,
+		u, v, w float,
+	)
 
-	MultiLineSignature2(a, b,
+	MultiLineSignature2(
-		c int)
+		a, b,
+		c int,
+	)
 
-	MultiLineSignature3(a, b,
+	MultiLineSignature3(
+		a, b,
 		c int, u, v,
 		w float,
 		x ...int)
 
-	MultiLineSignature4(a, b, c int,
+	MultiLineSignature4(
+		a, b, c int,
 		u, v,
 		w float,
 		x ...int)
 
-	MultiLineSignature5(a, b, c int,
+	MultiLineSignature5(
+		a, b, c int,
 		u, v, w float,
 		p, q,
 		r string,

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

@@ -220,4 +220,56 @@ testLoop:
 	}
 }
 
+// Respect line breaks in function calls.
+func _() {
+	f(x)
+	f(x,
+		x)
+	f(x,
+		x,
+	)
+	f(
+		x,
+		x)
+	f(
+		x,
+		x,
+	)
+}
+
+// Respect line breaks in function declarations.
+func _(x T)	{}
+func _(x T,
+	y T) {
+}
+func _(x T,
+	y T,
+) {
+}
+func _(
+	x T,
+	y T) {
+}
+func _(
+	x T,
+	y T,
+) {
+}
+
+// Example from issue 2597.
+func ManageStatus0(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int) {
+}
+
+func ManageStatus1(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int,
+) {
+}
+
 // There should be exactly one linebreak after this comment.

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

@@ -220,4 +220,52 @@ testLoop:
 	}
 }
 
+// Respect line breaks in function calls.
+func _() {
+	f(x)
+	f(x,
+	  x)
+	f(x,
+	  x,
+	)
+	f(
+	  x,
+	  x)
+	f(
+	  x,
+	  x,
+	)
+}
+
+// Respect line breaks in function declarations.
+func _(x T) {}
+func _(x T,
+       y T) {}
+func _(x T,
+       y T,
+) {}
+func _(
+       x T,
+       y T) {}
+func _(
+       x T,
+       y T,
+) {}
+
+// Example from issue 2597.
+func ManageStatus0(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int) {
+}
+    
+func ManageStatus1(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int,
+) {
+}
+    
 // There should be exactly one linebreak after this comment.