- don't loose extra line breaks in struct/interface declarations

- start new sections if a field/method declaration spans multiple lines;
  this avoids tabs from the previous line affecting the next field/method

R=rsc
http://go/go-review/1017015

src/pkg/go/ast/ast.go

@@ -95,6 +95,14 @@ type Field struct {
 }
 
 
+func (f *Field) Pos() token.Position {
+	if len(f.Names) > 0 {
+		return f.Names[0].Pos();
+	}
+	return f.Type.Pos();
+}
+
+
 // An expression is represented by a tree consisting of one
 // or more of the following concrete expression nodes.
 //

src/pkg/go/printer/nodes.go

@@ -256,15 +256,16 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 			sep = blank;
 		}
 		for i, f := range list {
+			var ml bool;
 			extraTabs := 0;
 			p.leadComment(f.Doc);
 			if len(f.Names) > 0 {
-				p.identList(f.Names, ignoreMultiLine);
+				p.identList(f.Names, &ml);
 				p.print(sep);
-				p.expr(f.Type, ignoreMultiLine);
+				p.expr(f.Type, &ml);
 				extraTabs = 1;
 			} else {
-				p.expr(f.Type, ignoreMultiLine);
+				p.expr(f.Type, &ml);
 				extraTabs = 2;
 			}
 			if f.Tag != nil {
@@ -272,7 +273,7 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 					p.print(sep);
 				}
 				p.print(sep);
-				p.expr(&ast.StringList{f.Tag}, ignoreMultiLine);
+				p.expr(&ast.StringList{f.Tag}, &ml);
 				extraTabs = 0;
 			}
 			p.print(token.SEMICOLON);
@@ -282,8 +283,10 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 				}
 				p.lineComment(f.Comment);
 			}
-			if i+1 < len(list) || isIncomplete {
-				p.print(newline);
+			if i+1 < len(list) {
+				p.linebreak(list[i+1].Pos().Line, 1, 2, ignore, ml);
+			} else if isIncomplete {
+				p.print(formfeed);
 			}
 		}
 		if isIncomplete {
@@ -294,19 +297,22 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 	} else { // interface
 
 		for i, f := range list {
+			var ml bool;
 			p.leadComment(f.Doc);
 			if ftyp, isFtyp := f.Type.(*ast.FuncType); isFtyp {
 				// method
-				p.expr(f.Names[0], ignoreMultiLine);  // exactly one name
-				p.signature(ftyp.Params, ftyp.Results, ignoreMultiLine);
+				p.expr(f.Names[0], &ml);
+				p.signature(ftyp.Params, ftyp.Results, &ml);
 			} else {
 				// embedded interface
-				p.expr(f.Type, ignoreMultiLine);
+				p.expr(f.Type, &ml);
 			}
 			p.print(token.SEMICOLON);
 			p.lineComment(f.Comment);
-			if i+1 < len(list) || isIncomplete {
-				p.print(newline);
+			if i+1 < len(list) {
+				p.linebreak(list[i+1].Pos().Line, 1, 2, ignore, ml);
+			} else if isIncomplete {
+				p.print(formfeed);
 			}
 		}
 		if isIncomplete {

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

@@ -93,6 +93,53 @@ func _() {
 }
 
 
+// don't lose blank lines in this struct
+type _ struct {
+	String struct {
+		Str, Len int;
+	};
+	Slice struct {
+		Array, Len, Cap int;
+	};
+	Eface struct {
+		Typ, Ptr int;
+	};
+
+	UncommonType struct {
+		Name, PkgPath int;
+	};
+	CommonType struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int;
+	};
+	Type struct {
+		Typ, Ptr int;
+	};
+	StructField struct {
+		Name, PkgPath, Typ, Tag, Offset int;
+	};
+	StructType struct {
+		Fields int;
+	};
+	PtrType struct {
+		Elem int;
+	};
+	SliceType struct {
+		Elem int;
+	};
+	ArrayType struct {
+		Elem, Len int;
+	};
+
+	Stktop struct {
+		Stackguard, Stackbase, Gobuf int;
+	};
+	Gobuf struct {
+		Sp, Pc, G int;
+	};
+	G struct {
+		Stackbase, Sched, Status, Alllink int;
+	};
+}
 
 
 // no tabs for single or ungrouped decls

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

@@ -94,6 +94,55 @@ func _() {
 }
 
 
+// don't lose blank lines in this struct
+type _ struct {
+	String	struct {
+		Str, Len int;
+	};
+	Slice	struct {
+		Array, Len, Cap int;
+	};
+	Eface	struct {
+		Typ, Ptr int;
+	};
+
+	UncommonType	struct {
+		Name, PkgPath int;
+	};
+	CommonType	struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int;
+	};
+	Type	struct {
+		Typ, Ptr int;
+	};
+	StructField	struct {
+		Name, PkgPath, Typ, Tag, Offset int;
+	};
+	StructType	struct {
+		Fields int;
+	};
+	PtrType	struct {
+		Elem int;
+	};
+	SliceType	struct {
+		Elem int;
+	};
+	ArrayType	struct {
+		Elem, Len int;
+	};
+
+	Stktop	struct {
+		Stackguard, Stackbase, Gobuf int;
+	};
+	Gobuf	struct {
+		Sp, Pc, G int;
+	};
+	G	struct {
+		Stackbase, Sched, Status, Alllink int;
+	};
+}
+
+
 // no tabs for single or ungrouped decls
 func _() {
 	const xxxxxx = 0;