parse: Emit: pass a pointer to line with a request to not modify it

pkg/parse/parse.go

@@ -273,7 +273,7 @@ func ReadLog(r io.Reader, w io.Writer, ins *InputSchema, outs *OutputSchema, fil
 					outs.noMessage = ins.NoMessageKey
 					outs.suppressionConfigured = true
 				}
-				outs.Emit(*toEmit, buf)
+				outs.Emit(toEmit, buf)
 			}
 
 			// Copying the buffer to the output writer is handled in defer.
@@ -471,9 +471,8 @@ func (s *InputSchema) ReadLine(l *line) error {
 	return retErr
 }
 
-// Emit emits a formatted line to the provided buffer.  The provided line object may not be used
-// again until reinitialized.
-func (s *OutputSchema) Emit(l line, w *bytes.Buffer) {
+// Emit emits a formatted line to the provided buffer.  Emit must not mutate line.
+func (s *OutputSchema) Emit(l *line, w *bytes.Buffer) {
 	// Is this a line separating unrelated contexts?  If so, print a separator and do nothing else.
 	if l.isSeparator {
 		w.WriteString("---\n")

pkg/parse/parse_fuzz_test.go

@@ -136,7 +136,7 @@ func FuzzEmit(f *testing.F) {
 			fields:    fieldMap,
 		}
 		outbuf := new(bytes.Buffer)
-		outs.Emit(*l, outbuf)
+		outs.Emit(l, outbuf)
 		byts := outbuf.Bytes()
 		if len(byts) == 0 {
 			t.Fatal("no output produced")

pkg/parse/parse_test.go

@@ -604,7 +604,7 @@ func TestEmit(t *testing.T) {
 				PriorityFields: []string{"baz"},
 				state:          test.state,
 			}
-			s.Emit(test.line, w)
+			s.Emit(&test.line, w)
 			if diff := cmp.Diff(w.String(), test.want); diff != "" {
 				t.Errorf("emitted output:\n%v", diff)
 			}