[dev.typeparams] cmd/compile/internal/syntax: clean up node printing API

Preparation for using the syntax printer as expression printer in types2.

- Introduced Form to control printing format
- Cleaned up/added String and ShortString convenience functions
- Implemented ShortForm format which prints … for non-empty
  function and composite literal bodies
- Added test to check write error handling

Change-Id: Ie86e46d766fb60fcf07ef643c7788b2ef440ffa8
Reviewed-on: https://go-review.googlesource.com/c/go/+/282552
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 28 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/syntax/printer_test.go b/src/cmd/compile/internal/syntax/printer_test.go
index 9f1f7e18cb..6c07fe0a26 100644
--- a/src/cmd/compile/internal/syntax/printer_test.go
+++ b/src/cmd/compile/internal/syntax/printer_test.go
@@ -25,11 +25,38 @@ func TestPrint(t *testing.T) {
 	}
 
 	if ast != nil {
-		Fprint(testOut(), ast, true)
+		Fprint(testOut(), ast, LineForm)
 		fmt.Println()
 	}
 }
 
+type shortBuffer struct {
+	buf []byte
+}
+
+func (w *shortBuffer) Write(data []byte) (n int, err error) {
+	w.buf = append(w.buf, data...)
+	n = len(data)
+	if len(w.buf) > 10 {
+		err = io.ErrShortBuffer
+	}
+	return
+}
+
+func TestPrintError(t *testing.T) {
+	const src = "package p; var x int"
+	ast, err := Parse(nil, strings.NewReader(src), nil, nil, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf shortBuffer
+	_, err = Fprint(&buf, ast, 0)
+	if err == nil || err != io.ErrShortBuffer {
+		t.Errorf("got err = %s, want %s", err, io.ErrShortBuffer)
+	}
+}
+
 var stringTests = []string{
 	"package p",
 	"package p; type _ int; type T1 = struct{}; type ( _ *struct{}; T2 = float32 )",