From cabcc615c1b22101ce30121fcedee457a61559da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Tue, 14 Jul 2020 10:47:17 +0200
Subject: [PATCH] vt: change HT (horizontal tab) to *not* clear LCF

According to the specification, HT **should** clear LCF. However,
nearly all emulators do not. In particular, XTerm doesn't. So we
follow suite.
---
 CHANGELOG.md | 2 ++
 vt.c         | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bd172a47..1d18d1f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -96,6 +96,8 @@
   (https://codeberg.org/dnkl/foot/issues/35).
 * `C0::VT` to be processed as `C0::LF`. Previously, `C0::VT` would
   only move the cursor down, but never scroll.
+* HT (_Horizontal Tab_, or `\t`) no longer clears `LCF` (_Last Column
+  Flag_).
 
 
 ### Security
diff --git a/vt.c b/vt.c
index 1254d28b..8d9d6cfa 100644
--- a/vt.c
+++ b/vt.c
@@ -142,7 +142,13 @@ action_execute(struct terminal *term, uint8_t c)
             }
         }
         assert(new_col >= term->grid->cursor.point.col);
+
+        /* According to the specification, HT _should_ cancel LCF. But
+         * XTerm, and nearly all other emulators, don't. So we follow
+         * suite */
+        bool lcf = term->grid->cursor.lcf;
         term_cursor_right(term, new_col - term->grid->cursor.point.col);
+        term->grid->cursor.lcf = lcf;
         break;
     }