insert-mode: interpret unmapped META as ESC

closes #2454
closes #8213
ref #7972

3 files changed, 18 insertions, 12 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index b772a944f4..117d89d24c 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -847,7 +847,7 @@ static int insert_handle_key(InsertState *s)
 
 
   case ' ':
-    if (mod_mask != 4) {
+    if (mod_mask != MOD_MASK_CTRL) {
       goto normalchar;
     }
   // FALLTHROUGH
@@ -1180,6 +1180,14 @@ static int insert_handle_key(InsertState *s)
 
 normalchar:
     // Insert a normal character.
+
+    if (mod_mask == MOD_MASK_ALT || mod_mask == MOD_MASK_META) {
+      // Unmapped ALT/META chord behaves like ESC+c. #8213
+      stuffcharReadbuff(ESC);
+      stuffcharReadbuff(s->c);
+      break;
+    }
+
     if (!p_paste) {
       // Trigger InsertCharPre.
       char_u *str = do_insert_char_pre(s->c);
@@ -1432,7 +1440,7 @@ static void ins_ctrl_v(void)
      * line and will not removed by the redraw */
     edit_unputchar();
   clear_showcmd();
-  insert_special(c, FALSE, TRUE);
+  insert_special(c, true, true);
   revins_chars++;
   revins_legal++;
 }
@@ -5054,13 +5062,11 @@ static void insert_special(int c, int allow_modmask, int ctrlv)
   char_u  *p;
   int len;
 
-  /*
-   * Special function key, translate into "<Key>". Up to the last '>' is
-   * inserted with ins_str(), so as not to replace characters in replace
-   * mode.
-   * Only use mod_mask for special keys, to avoid things like <S-Space>,
-   * unless 'allow_modmask' is TRUE.
-   */
+  // Special function key, translate into "<Key>". Up to the last '>' is
+  // inserted with ins_str(), so as not to replace characters in replace
+  // mode.
+  // 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;
   }
diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index 5d4e61d56a..03929a58b6 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -1577,7 +1577,7 @@ vungetc ( /* unget one character (can only be done once!) */
   old_mouse_col = mouse_col;
 }
 
-/// get a character:
+/// Gets a character:
 /// 1. from the stuffbuffer
 ///    This is used for abbreviated commands like "D" -> "d$".
 ///    Also used to redo a command for ".".
@@ -1595,7 +1595,7 @@ vungetc ( /* unget one character (can only be done once!) */
 /// if "advance" is FALSE (vpeekc()):
 ///    just look whether there is a character available.
 ///
-/// When "no_mapping" is zero, checks for mappings in the current mode.
+/// When `no_mapping` (global) is zero, checks for mappings in the current mode.
 /// Only returns one byte (of a multi-byte character).
 /// K_SPECIAL and CSI may be escaped, need to get two more bytes then.
 static int vgetorpeek(int advance)
diff --git a/src/nvim/keymap.h b/src/nvim/keymap.h
index 00e9cf6ed3..c64691e8ea 100644
--- a/src/nvim/keymap.h
+++ b/src/nvim/keymap.h
@@ -443,7 +443,7 @@ enum key_extra {
 #define MOD_MASK_2CLICK     0x20        // use MOD_MASK_MULTI_CLICK
 #define MOD_MASK_3CLICK     0x40        // use MOD_MASK_MULTI_CLICK
 #define MOD_MASK_4CLICK     0x60        // use MOD_MASK_MULTI_CLICK
-#define MOD_MASK_CMD        0x80        // "super" key (OSX/Mac: command-key)
+#define MOD_MASK_CMD        0x80        // "super" key (macOS: command-key)
 
 #define MOD_MASK_MULTI_CLICK    (MOD_MASK_2CLICK|MOD_MASK_3CLICK| \
                                  MOD_MASK_4CLICK)