1 files changed, 68 insertions, 7 deletions

diff --git a/libgo/go/go/printer/printer_test.go b/libgo/go/go/printer/printer_test.go
index 525fcc1595f..9adf48cda61 100644
--- a/libgo/go/go/printer/printer_test.go
+++ b/libgo/go/go/printer/printer_test.go
@@ -171,14 +171,14 @@ func TestLineComments(t *testing.T) {
 	`
 
 	fset := token.NewFileSet()
-	ast1, err1 := parser.ParseFile(fset, "", src, parser.ParseComments)
-	if err1 != nil {
-		panic(err1)
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		panic(err) // error in test
 	}
 
 	var buf bytes.Buffer
 	fset = token.NewFileSet() // use the wrong file set
-	Fprint(&buf, fset, ast1)
+	Fprint(&buf, fset, f)
 
 	nlines := 0
 	for _, ch := range buf.Bytes() {
@@ -190,6 +190,7 @@ func TestLineComments(t *testing.T) {
 	const expected = 3
 	if nlines < expected {
 		t.Errorf("got %d, expected %d\n", nlines, expected)
+		t.Errorf("result:\n%s", buf.Bytes())
 	}
 }
 
@@ -198,9 +199,11 @@ func init() {
 	const name = "foobar"
 	var buf bytes.Buffer
 	if err := Fprint(&buf, fset, &ast.Ident{Name: name}); err != nil {
-		panic(err)
+		panic(err) // error in test
 	}
-	if s := buf.String(); s != name {
+	// in debug mode, the result contains additional information;
+	// ignore it
+	if s := buf.String(); !debug && s != name {
 		panic("got " + s + ", want " + name)
 	}
 }
@@ -211,7 +214,7 @@ func TestBadNodes(t *testing.T) {
 	const res = "package p\nBadDecl\n"
 	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
 	if err == nil {
-		t.Errorf("expected illegal program")
+		t.Error("expected illegal program") // error in test
 	}
 	var buf bytes.Buffer
 	Fprint(&buf, fset, f)
@@ -219,3 +222,61 @@ func TestBadNodes(t *testing.T) {
 		t.Errorf("got %q, expected %q", buf.String(), res)
 	}
 }
+
+// Print and parse f with 
+func testComment(t *testing.T, f *ast.File, srclen int, comment *ast.Comment) {
+	f.Comments[0].List[0] = comment
+	var buf bytes.Buffer
+	for offs := 0; offs <= srclen; offs++ {
+		buf.Reset()
+		// Printing f should result in a correct program no
+		// matter what the (incorrect) comment position is.
+		if err := Fprint(&buf, fset, f); err != nil {
+			t.Error(err)
+		}
+		if _, err := parser.ParseFile(fset, "", buf.Bytes(), 0); err != nil {
+			t.Fatalf("incorrect program for pos = %d:\n%s", comment.Slash, buf.String())
+		}
+		// Position information is just an offset.
+		// Move comment one byte down in the source.
+		comment.Slash++
+	}
+}
+
+// Verify that the printer produces always produces a correct program
+// even if the position information of comments introducing newlines
+// is incorrect.
+func TestBadComments(t *testing.T) {
+	const src = `
+// first comment - text and position changed by test
+package p
+import "fmt"
+const pi = 3.14 // rough circle
+var (
+	x, y, z int = 1, 2, 3
+	u, v float64
+)
+func fibo(n int) {
+	if n < 2 {
+		return n /* seed values */
+	}
+	return fibo(n-1) + fibo(n-2)
+}
+`
+
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		t.Error(err) // error in test
+	}
+
+	comment := f.Comments[0].List[0]
+	pos := comment.Pos()
+	if fset.Position(pos).Offset != 1 {
+		t.Error("expected offset 1") // error in test
+	}
+
+	testComment(t, f, len(src), &ast.Comment{pos, "//-style comment"})
+	testComment(t, f, len(src), &ast.Comment{pos, "/*-style comment */"})
+	testComment(t, f, len(src), &ast.Comment{pos, "/*-style \n comment */"})
+	testComment(t, f, len(src), &ast.Comment{pos, "/*-style comment \n\n\n */"})
+}