keymap: Support <D-...> (super/command key).

Adds support for:
  - api:vim_input("<D-a>")
  - ":nnoremap <C-D-S-...>" and permutations thereof

UIs must capture the modifier and send it as "<D-...>" to vim_input().

Note: Before this commit, any arbitrary ":nnoremap <{foo}-{bar}>"
mapping could already be invoked with feedkeys("\<{foo}-{bar}>"). This
commit supports "D-" as a modifier that can be combined with "C-", "A-",
"S-" in any order.

For non-GUI (terminal) support, user must:
  :set <D-a>={CSI sequence}
then send the {CSI sequence} from their terminal. But this does not work
yet (regression #2204).

Closes #2190

1 files changed, 7 insertions, 9 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index d3b556f669..a983fa5772 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -4947,15 +4947,10 @@ int get_literal(void)
   return cc;
 }
 
-/*
- * Insert character, taking care of special keys and mod_mask
- */
-static void
-insert_special (
-    int c,
-    int allow_modmask,
-    int ctrlv                  /* c was typed after CTRL-V */
-)
+/// Insert character, taking care of special keys and mod_mask
+///
+/// @param ctrlv `c` was typed after CTRL-V
+static void insert_special(int c, int allow_modmask, int ctrlv)
 {
   char_u  *p;
   int len;
@@ -4967,6 +4962,9 @@ insert_special (
    * Only use mod_mask for special keys, to avoid things like <S-Space>,
    * unless 'allow_modmask' is TRUE.
    */
+  if (mod_mask & MOD_MASK_CMD) {  // Command-key never produces a normal key.
+    allow_modmask = true;
+  }
   if (IS_SPECIAL(c) || (mod_mask && allow_modmask)) {
     p = get_special_key_name(c, mod_mask);
     len = (int)STRLEN(p);