From 31c73f0cf01e1d0bdcd1435136b010c1c1ab442c Mon Sep 17 00:00:00 2001
From: Craig Barnes <craigbarnes@protonmail.com>
Date: Sun, 29 Nov 2020 04:04:57 +0000
Subject: [PATCH] csi: add new private mode that makes the Escape key emit
 "\E[27;1;27~"

This mode can be set by client programs with the DECSET, DECRST,
XTSAVE and XTRESTORE sequences by using 27127 as the parameter.

The sequence "\E[27;1;27~" is encoded in the same way as is done by
xterm's "modifyOtherKeys" mode. Even though xterm itself never emits
such a sequence for the Escape key, many programs already have
support for parsing this style of key sequence.
---
 csi.c      | 6 ++++++
 input.c    | 8 +++++++-
 terminal.c | 1 +
 terminal.h | 2 ++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/csi.c b/csi.c
index e4975583..f70c58b2 100644
--- a/csi.c
+++ b/csi.c
@@ -536,6 +536,10 @@ decset_decrst(struct terminal *term, unsigned param, bool enable)
         term->bracketed_paste = enable;
         break;
 
+    case 27127:
+        term->modify_escape_key = enable;
+        break;
+
     default:
         UNHANDLED();
         break;
@@ -583,6 +587,7 @@ xtsave(struct terminal *term, unsigned param)
     case 1042: term->xtsave.bell_is_urgent = term->bell_is_urgent; break;
     case 1049: term->xtsave.alt_screen = term->grid == &term->alt; break;
     case 2004: term->xtsave.bracketed_paste = term->bracketed_paste; break;
+    case 27127: term->xtsave.modify_escape_key = term->modify_escape_key; break;
     }
 }
 
@@ -616,6 +621,7 @@ xtrestore(struct terminal *term, unsigned param)
     case 1042: enable = term->xtsave.bell_is_urgent; break;
     case 1049: enable = term->xtsave.alt_screen; break;
     case 2004: enable = term->xtsave.bracketed_paste; break;
+    case 27127: enable = term->xtsave.modify_escape_key; break;
 
     default: return;
     }
diff --git a/input.c b/input.c
index 61f1d004..191a3de9 100644
--- a/input.c
+++ b/input.c
@@ -891,7 +891,13 @@ key_press_release(struct seat *seat, struct terminal *term, uint32_t serial,
     keymap_mods |= seat->kbd.ctrl ? MOD_CTRL : MOD_NONE;
     keymap_mods |= seat->kbd.meta ? MOD_META : MOD_NONE;
 
-    const struct key_data *keymap = keymap_lookup(seat, term, sym, keymap_mods);
+    const struct key_data *keymap;
+    if (sym == XKB_KEY_Escape && keymap_mods == MOD_NONE && term->modify_escape_key) {
+        static const struct key_data esc = {.seq = "\033[27;1;27~"};
+        keymap = &esc;
+    } else
+        keymap = keymap_lookup(seat, term, sym, keymap_mods);
+
     if (keymap != NULL) {
         term_to_slave(term, keymap->seq, strlen(keymap->seq));
 
diff --git a/terminal.c b/terminal.c
index 6a20056c..3bb41d12 100644
--- a/terminal.c
+++ b/terminal.c
@@ -1523,6 +1523,7 @@ term_reset(struct terminal *term, bool hard)
     term->insert_mode = false;
     term->bracketed_paste = false;
     term->focus_events = false;
+    term->modify_escape_key = false;
     term->mouse_tracking = MOUSE_NONE;
     term->mouse_reporting = MOUSE_NORMAL;
     term->charsets.selected = 0;
diff --git a/terminal.h b/terminal.h
index ea49edf2..4eca0aa9 100644
--- a/terminal.h
+++ b/terminal.h
@@ -236,6 +236,7 @@ struct terminal {
     bool bracketed_paste;
     bool focus_events;
     bool alt_scrolling;
+    bool modify_escape_key;
     enum cursor_origin origin;
     enum cursor_keys cursor_keys_mode;
     enum keypad_keys keypad_keys_mode;
@@ -296,6 +297,7 @@ struct terminal {
         uint32_t num_lock_modifier:1;
         uint32_t bell_is_urgent:1;
         uint32_t alt_screen:1;
+        uint32_t modify_escape_key:1;
     } xtsave;
 
     char *window_title;