Key encoding: in legacy mode use legacy encoding for a few more combinations

Some legacy terminal applications get confused seeing CSI u escape
codes. Since it is relatively common to press ctrl or shift and
space/enter/tab/backspace, emit the same bytes as traditional terminals
do for these common keys.

docs/keyboard-protocol.rst

@@ -415,17 +415,18 @@ mode* (the ``smkx/rmkx`` terminfo capabilities). This form is used only in
     "F11",       "kf11",       "CSI 23 ~"
     "F12",       "kf12",       "CSI 24 ~"
 
-There are a few more functional keys that have special cased legacy
+There are a few more functional keys that have special cased legacy encodings.
-encodings:
+These are present because they are commonly used and for the sake of legacy
+terminal applications that get confused when seeing CSI u escape codes:
 
 .. csv-table:: C0 controls
-    :header: "Key", "Encodings"
+    :header: "Key", "No mods", "Ctrl", "Alt", "Shift", "Ctrl + Shift", "Alt + Shift", "Ctrl + Alt"
 
-    "Enter",     "Plain - 0xd,  alt+Enter - 0x1b 0x1d"
+    "Enter",     "0xd",  "0xd",  "0x1b 0xd",  "0xd",   "0xd",   "0x1b 0xd",   "0x1b 0xd"
-    "Escape",    "Plain - 0x1b, alt+Esc - 0x1b 0x1b"
+    "Escape",    "0x1b", "0x1b", "0x1b 0x1b", "0x1b",  "0x1b",  "0x1b 0x1b",  "0x1b 0x1b"
-    "Backspace", "Plain - 0x7f, alt+Backspace - 0x1b 0x7f, ctrl+Backspace - 0x08"
+    "Backspace", "0x7f", "0x8",  "0x1b 0x7f", "0x7f",  "0x8",   "0x1b 0x7f",  "0x1b 0x8"
-    "Space",     "Plain - 0x20, ctrl+Space - 0x0, alt+space - 0x1b 0x20"
+    "Tab",       "0x9",  "0x9",  "0x1b 0x9",  "CSI Z", "CSI Z", "0x1b CSI Z", "0x1b 0x9"
-    "Tab",       "Plain - 0x09, shift+Tab - CSI Z"
+    "Space",     "0x20", "0x0",  "0x1b 0x20", "0x20",  "0x0",   "0x1b 0x20",  "0x1b 0x0"
 
 Note that :kbd:`Backspace` and :kbd:`ctrl+Backspace` are swapped in some
 terminals, this can be detected using the ``kbs`` terminfo property that

kitty/key_encoding.c

@@ -126,6 +126,34 @@ convert_kp_key_to_normal_key(uint32_t key_number) {
     return key_number;
 }
 
+static int
+legacy_functional_key_encoding_with_modifiers(uint32_t key_number, const KeyEvent *ev, char *output) {
+    const char *prefix = ev->mods.value & ALT ? "\x1b" : "";
+    const char *main = "";
+    switch (key_number) {
+        case GLFW_FKEY_ENTER:
+            main = "\x0d";
+            break;
+        case GLFW_FKEY_ESCAPE:
+            main = "\x1b";
+            break;
+        case GLFW_FKEY_BACKSPACE:
+            main = ev->mods.value & CTRL ? "\x08" : "\x7f";
+            break;
+        case GLFW_FKEY_TAB:
+            if (ev->mods.value & SHIFT) {
+                prefix = ev->mods.value & ALT ? "\x1b\x1b" : "\x1b";
+                main = "[Z";
+            } else {
+                main = "\t";
+            }
+            break;
+        default:
+            return -1;
+    }
+    return snprintf(output, KEY_BUFFER_SIZE, "%s%s", prefix, main);
+}
+
 static int
 encode_function_key(const KeyEvent *ev, char *output) {
 #define SIMPLE(val) return snprintf(output, KEY_BUFFER_SIZE, "%s", val);
@@ -158,18 +186,11 @@ encode_function_key(const KeyEvent *ev, char *output) {
                 default: break;
             }
         }
+    } else if (legacy_mode) {
+        int num = legacy_functional_key_encoding_with_modifiers(key_number, ev, output);
+        if (num > -1) return num;
     }
-    if (ev->mods.value == ALT && !ev->disambiguate) {
-        switch(key_number) {
-            case GLFW_FKEY_TAB: SIMPLE("\x1b\t");
-            case GLFW_FKEY_ENTER: SIMPLE("\x1b\r");
-            case GLFW_FKEY_BACKSPACE: SIMPLE("\x1b\x7f");
-        }
-    }
-    if (ev->mods.value == SHIFT && key_number == GLFW_FKEY_TAB && !ev->disambiguate) { SIMPLE("\x1b[Z"); }
-    if (ev->mods.value == CTRL && key_number == GLFW_FKEY_BACKSPACE && !ev->disambiguate) { SIMPLE("\x08"); }
 #undef SIMPLE
-
 #define S(number, trailer) key_number = number; csi_trailer = trailer; break
     switch(key_number) {
         /* start special numbers (auto generated by gen-key-constants.py do not edit) */
@@ -288,6 +309,10 @@ encode_printable_ascii_key_legacy(const KeyEvent *ev, char *output) {
         return snprintf(output, KEY_BUFFER_SIZE, "%c", ctrled_key(key));
     if (mods == (CTRL | ALT))
         return snprintf(output, KEY_BUFFER_SIZE, "\x1b%c", ctrled_key(key));
+    if (key == ' ') {
+        if (mods == (CTRL | SHIFT)) return snprintf(output, KEY_BUFFER_SIZE, "%c", ctrled_key(key));
+        if (mods == (ALT  | SHIFT)) return snprintf(output, KEY_BUFFER_SIZE, "\x1b%c", key);
+    }
     return 0;
 }
 

kitty_tests/keys.py

@@ -60,29 +60,32 @@ class TestKeys(BaseTest):
 
             def a(a, b):
                 ae(a, b, f"{a.encode('ascii')} != {b.encode('ascii')}")
-            a(e(), plain or c())
-            a(e(mods=defines.GLFW_MOD_SHIFT), shift or c(defines.GLFW_MOD_SHIFT))
-            a(e(mods=defines.GLFW_MOD_CONTROL), ctrl or c(defines.GLFW_MOD_CONTROL))
-            a(e(mods=defines.GLFW_MOD_ALT | defines.GLFW_MOD_CONTROL), calt or c(defines.GLFW_MOD_ALT | defines.GLFW_MOD_CONTROL))
-            a(e(mods=defines.GLFW_MOD_SHIFT | defines.GLFW_MOD_CONTROL), cshift or c(defines.GLFW_MOD_CONTROL | defines.GLFW_MOD_SHIFT))
-            a(e(mods=defines.GLFW_MOD_SHIFT | defines.GLFW_MOD_ALT), ashift or c(defines.GLFW_MOD_ALT | defines.GLFW_MOD_SHIFT))
 
-        mods_test(defines.GLFW_FKEY_ENTER, '\x0d', alt='\033\x0d', csi_num=ord('\r'))
+            def w(a, b):
-        mods_test(defines.GLFW_FKEY_KP_ENTER, '\x0d', alt='\033\x0d', csi_num=ord('\r'))
+                return c(b) if a is None else a
-        mods_test(defines.GLFW_FKEY_ESCAPE, '\x1b', alt='\033\033', csi_num=27)
+
-        mods_test(defines.GLFW_FKEY_BACKSPACE, '\x7f', alt='\033\x7f', ctrl='\x08', csi_num=127)
+            a(e(), plain or c())
-        mods_test(defines.GLFW_FKEY_TAB, '\t', alt='\033\t', shift='\x1b[Z', csi_num=ord('\t'))
+            a(e(mods=defines.GLFW_MOD_SHIFT), w(shift, defines.GLFW_MOD_SHIFT))
-        mods_test(defines.GLFW_FKEY_INSERT, csi_num=2, trailer='~')
+            a(e(mods=defines.GLFW_MOD_CONTROL), w(ctrl, defines.GLFW_MOD_CONTROL))
-        mods_test(defines.GLFW_FKEY_KP_INSERT, csi_num=2, trailer='~')
+            a(e(mods=defines.GLFW_MOD_ALT | defines.GLFW_MOD_CONTROL), w(calt, defines.GLFW_MOD_ALT | defines.GLFW_MOD_CONTROL))
-        mods_test(defines.GLFW_FKEY_DELETE, csi_num=3, trailer='~')
+            a(e(mods=defines.GLFW_MOD_SHIFT | defines.GLFW_MOD_CONTROL), w(cshift, defines.GLFW_MOD_CONTROL | defines.GLFW_MOD_SHIFT))
-        mods_test(defines.GLFW_FKEY_KP_DELETE, csi_num=3, trailer='~')
+            a(e(mods=defines.GLFW_MOD_SHIFT | defines.GLFW_MOD_ALT), w(ashift, defines.GLFW_MOD_ALT | defines.GLFW_MOD_SHIFT))
-        mods_test(defines.GLFW_FKEY_PAGE_UP, csi_num=5, trailer='~')
+
-        mods_test(defines.GLFW_FKEY_KP_PAGE_UP, csi_num=5, trailer='~')
+        def mkp(name, *a, **kw):
-        mods_test(defines.GLFW_FKEY_KP_PAGE_DOWN, csi_num=6, trailer='~')
+            for x in (f'GLFW_FKEY_{name}', f'GLFW_FKEY_KP_{name}'):
-        mods_test(defines.GLFW_FKEY_HOME, csi_num=1, trailer='H')
+                k = getattr(defines, x)
-        mods_test(defines.GLFW_FKEY_KP_HOME, csi_num=1, trailer='H')
+                mods_test(k, *a, **kw)
-        mods_test(defines.GLFW_FKEY_END, csi_num=1, trailer='F')
+
-        mods_test(defines.GLFW_FKEY_KP_END, csi_num=1, trailer='F')
+        mkp('ENTER', '\x0d', alt='\033\x0d', ctrl='\x0d', shift='\x0d', ashift='\033\x0d', calt='\033\x0d', cshift='\x0d')
+        mods_test(defines.GLFW_FKEY_ESCAPE, '\x1b', alt='\033\033', ctrl='\x1b', shift='\x1b', calt='\x1b\x1b', cshift='\x1b', ashift='\x1b\x1b')
+        mods_test(defines.GLFW_FKEY_BACKSPACE, '\x7f', alt='\033\x7f', ctrl='\x08', shift='\x7f', ashift='\033\x7f', cshift='\x08', calt='\x1b\x08')
+        mods_test(defines.GLFW_FKEY_TAB, '\t', alt='\033\t', shift='\x1b[Z', ctrl='\t', ashift='\x1b\x1b[Z', cshift='\x1b[Z', calt='\x1b\t')
+        mkp('INSERT', csi_num=2, trailer='~')
+        mkp('DELETE', csi_num=3, trailer='~')
+        mkp('PAGE_UP', csi_num=5, trailer='~')
+        mkp('PAGE_DOWN', csi_num=6, trailer='~')
+        mkp('HOME', csi_num=1, trailer='H')
+        mkp('END', csi_num=1, trailer='F')
         mods_test(defines.GLFW_FKEY_F1, csi_num=1, trailer='P')
         mods_test(defines.GLFW_FKEY_F2, csi_num=1, trailer='Q')
         mods_test(defines.GLFW_FKEY_F3, csi_num=1, trailer='R')
@@ -95,14 +98,10 @@ class TestKeys(BaseTest):
         mods_test(defines.GLFW_FKEY_F10, csi_num=21, trailer='~')
         mods_test(defines.GLFW_FKEY_F11, csi_num=23, trailer='~')
         mods_test(defines.GLFW_FKEY_F12, csi_num=24, trailer='~')
-        mods_test(defines.GLFW_FKEY_UP, csi_num=1, trailer='A')
+        mkp('UP', csi_num=1, trailer='A')
-        mods_test(defines.GLFW_FKEY_KP_UP, csi_num=1, trailer='A')
+        mkp('DOWN', csi_num=1, trailer='B')
-        mods_test(defines.GLFW_FKEY_DOWN, csi_num=1, trailer='B')
+        mkp('RIGHT', csi_num=1, trailer='C')
-        mods_test(defines.GLFW_FKEY_KP_DOWN, csi_num=1, trailer='B')
+        mkp('LEFT', csi_num=1, trailer='D')
-        mods_test(defines.GLFW_FKEY_RIGHT, csi_num=1, trailer='C')
-        mods_test(defines.GLFW_FKEY_KP_RIGHT, csi_num=1, trailer='C')
-        mods_test(defines.GLFW_FKEY_LEFT, csi_num=1, trailer='D')
-        mods_test(defines.GLFW_FKEY_KP_LEFT, csi_num=1, trailer='D')
 
         # legacy key tests {{{
         # start legacy letter tests (auto generated by gen-key-constants.py do not edit)
@@ -397,6 +396,10 @@ class TestKeys(BaseTest):
         ae(enc(key=ord(' ')), ' ')
         ae(enc(key=ord(' '), mods=ctrl), '\0')
         ae(enc(key=ord(' '), mods=alt), '\x1b ')
+        ae(enc(key=ord(' '), mods=shift), ' ')
+        ae(enc(key=ord(' '), mods=ctrl | alt), '\x1b\0')
+        ae(enc(key=ord(' '), mods=ctrl | shift), '\0')
+        ae(enc(key=ord(' '), mods=alt | shift), '\x1b ')
         ae(enc(key=ord('i'), mods=ctrl | shift), csi(ctrl | shift, ord('i')))
         ae(enc(key=defines.GLFW_FKEY_LEFT_SHIFT), '')
         ae(enc(key=defines.GLFW_FKEY_CAPS_LOCK), '')