[vte] parser: cat: Make linter warn on unsupported RLogin DECGCI extension

[Christian Persch <chpe src gnome org>]

commit 9936d4d75b30793ca9f4f1baeda9270fa95562ee
Author: Christian Persch <chpe src gnome org>
Date:   Thu Feb 4 18:40:51 2021 +0100

    parser: cat: Make linter warn on unsupported RLogin DECGCI extension

 src/parser-cat.cc | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/src/parser-cat.cc b/src/parser-cat.cc
index 564ab739..fec7d1b1 100644
--- a/src/parser-cat.cc
+++ b/src/parser-cat.cc
@@ -836,6 +836,12 @@ public:
                                         break;
                                 }
 
+                                case 3: /* RGB truecolour.
+                                         * This is an RLogin extension and not supported by VTE.
+                                         */
+                                        warn("DECGCI RGB truecolour extension is not supported");
+                                        break;
+
                                 case 0:
                                 default:
                                         warn("DECGCI unknown colour coordinate system %d", seq.param(1));