only record explicit params (don't default to 0)

parser.go

@@ -55,6 +55,7 @@ type Parser struct {
 	intermediateIdx int
 	params          *params
 	param           uint16
+	hasParam        bool
 	oscRaw          []byte
 	oscParams       [maxOscParams][2]int
 	oscNumParams    int
@@ -311,7 +312,7 @@ func (p *Parser) performAction(action, b byte) {
 	case CsiDispatchAction:
 		if p.params.IsFull() {
 			p.ignoring = true
-		} else {
+		} else if p.hasParam {
 			p.params.Push(p.param)
 		}
 
@@ -346,19 +347,26 @@ func (p *Parser) performAction(action, b byte) {
 		if b == ';' {
 			p.params.Push(p.param)
 			p.param = 0
+			// accept a 0 for the following param even if we don't see a
+			// number, since the semicolon makes it obvious that a value should
+			// be there.
+			p.hasParam = true
 		} else if b == ':' {
 			p.params.Extend(p.param)
 			p.param = 0
+			p.hasParam = false
 		} else {
 			p.param = smulu16(p.param, 10)
 			p.param = saddu16(p.param, uint16((b - '0')))
+			p.hasParam = true
 		}
 
 	case ClearAction:
 		// Reset everything on ESC/CSI/DCS entry
 		p.intermediateIdx = 0
 		p.ignoring = false
 		p.param = 0
+		p.hasParam = false
 
 		p.params.Clear()
 

parser_csi_test.go

@@ -58,6 +58,24 @@ func TestCsiParamsIgnoreLong(t *testing.T) {
 	assert.Equal(t, expected, dispatcher.dispatched[0])
 }
 
+func TestCsiNoParams(t *testing.T) {
+	expected := testCsiSequence{
+		intermediates: []byte{},
+		ignore:        false,
+		rune:          'C',
+	}
+
+	dispatcher := &testDispatcher{}
+	parser := NewParser(dispatcher)
+
+	for _, b := range []byte("\x1b[C") {
+		parser.Advance(b)
+	}
+
+	assert.Equal(t, 1, len(dispatcher.dispatched))
+	assert.Equal(t, expected, dispatcher.dispatched[0])
+}
+
 func TestCsiParamsTrailingSemicolon(t *testing.T) {
 	expected := testCsiSequence{
 		params:        [][]uint16{{4}, {0}},