- respect source line breaks in grouped declarations

- made ast.Spec nodes implement Node interface
- added extra test cases

R=rsc
http://go/go-review/1016038

src/pkg/go/ast/ast.go

@@ -596,6 +596,7 @@ func (s *RangeStmt) stmtNode() {}
 type (
 	// The Spec type stands for any of *ImportSpec, *ValueSpec, and *TypeSpec.
 	Spec	interface {
+		Node;
 		specNode();
 	};
 
@@ -627,6 +628,23 @@ type (
 )
 
 
+// Pos() implementations for spec nodes.
+//
+func (s *ImportSpec) Pos() token.Position {
+	if s.Name != nil {
+		return s.Name.Pos();
+	}
+	return s.Path[0].Pos();
+}
+
+func (s *ValueSpec) Pos() token.Position {
+	return s.Names[0].Pos();
+}
+func (s *TypeSpec) Pos() token.Position {
+	return s.Name.Pos();
+}
+
+
 // specNode() ensures that only spec nodes can be
 // assigned to a Spec.
 //

src/pkg/go/printer/nodes.go

@@ -255,8 +255,12 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 		if len(list) == 1 {
 			sep = blank;
 		}
+		var ml bool;
 		for i, f := range list {
-			var ml bool;
+			if i > 0 {
+				p.linebreak(f.Pos().Line, 1, 2, ignore, ml);
+			}
+			ml = false;
 			extraTabs := 0;
 			p.leadComment(f.Doc);
 			if len(f.Names) > 0 {
@@ -283,21 +287,23 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 				}
 				p.lineComment(f.Comment);
 			}
-			if i+1 < len(list) {
-				p.linebreak(list[i+1].Pos().Line, 1, 2, ignore, ml);
-			} else if isIncomplete {
-				p.print(formfeed);
-			}
 		}
 		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed);
+			}
 			// TODO(gri): this needs to be styled like normal comments
 			p.print("// contains unexported fields");
 		}
 
 	} else { // interface
 
+		var ml bool;
 		for i, f := range list {
-			var ml bool;
+			if i > 0 {
+				p.linebreak(f.Pos().Line, 1, 2, ignore, ml);
+			}
+			ml = false;
 			p.leadComment(f.Doc);
 			if ftyp, isFtyp := f.Type.(*ast.FuncType); isFtyp {
 				// method
@@ -309,13 +315,11 @@ func (p *printer) fieldList(lbrace token.Position, list []*ast.Field, rbrace tok
 			}
 			p.print(token.SEMICOLON);
 			p.lineComment(f.Comment);
-			if i+1 < len(list) {
-				p.linebreak(list[i+1].Pos().Line, 1, 2, ignore, ml);
-			} else if isIncomplete {
-				p.print(formfeed);
-			}
 		}
 		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed);
+			}
 			// TODO(gri): this needs to be styled like normal comments
 			p.print("// contains unexported methods");
 		}
@@ -941,11 +945,7 @@ func (p *printer) genDecl(d *ast.GenDecl, context declContext, multiLine *bool)
 			var ml bool;
 			for i, s := range d.Specs {
 				if i > 0 {
-					if ml {
-						p.print(formfeed);
-					} else {
-						p.print(newline);
-					}
+					p.linebreak(s.Pos().Line, 1, 2, ignore, ml);
 				}
 				ml = false;
 				p.spec(s, len(d.Specs), inGroup, &ml);

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

@@ -21,6 +21,7 @@ import (
 import (
 	"io";
 	aLongRename "io";
+
 	b "io";
 	c "i" "o";
 )
@@ -93,6 +94,47 @@ func _() {
 }
 
 
+// don't lose blank lines in grouped declarations
+const (
+	_ int = 0;
+	_ float = 1;
+
+	_ string = "foo";
+
+	_ = iota;
+	_;
+	
+	// a comment
+	_;
+
+	_;
+)
+
+
+type (
+	_ int;
+	_ struct {};
+	
+	_ interface{};
+	
+	// a comment
+	_ map[string]int;
+)
+
+
+var (
+	_ int = 0;
+	_ float = 1;
+
+	_ string = "foo";
+
+	_ bool;
+	
+	// a comment
+	_ bool;
+)
+
+
 // don't lose blank lines in this struct
 type _ struct {
 	String struct {

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

@@ -21,6 +21,7 @@ import (
 import (
 	"io";
 	aLongRename "io";
+
 	b "io";
 	c "i" "o";
 )
@@ -94,6 +95,47 @@ func _() {
 }
 
 
+// don't lose blank lines in grouped declarations
+const (
+	_	int	= 0;
+	_	float	= 1;
+
+	_	string	= "foo";
+
+	_	= iota;
+	_;
+
+	// a comment
+	_;
+
+	_;
+)
+
+
+type (
+	_	int;
+	_	struct{};
+
+	_	interface{};
+
+	// a comment
+	_	map[string]int;
+)
+
+
+var (
+	_	int	= 0;
+	_	float	= 1;
+
+	_	string	= "foo";
+
+	_	bool;
+
+	// a comment
+	_	bool;
+)
+
+
 // don't lose blank lines in this struct
 type _ struct {
 	String	struct {
@@ -200,6 +242,7 @@ func _() {
 		_	int;
 		_	float;
 		_	string;
+
 		_	int;	// comment
 		_	float;	// comment
 		_	string;	// comment