vim-patch:9.0.0806: 'langmap' works differently when there are modifiers

Problem:    'langmap' works differently when there are modifiers.
Solution:   Only apply 'langmap' to a character where modifiers have no
            effect. (closes vim/vim#11395, closes vim/vim#11404)
49660f5139
(cherry picked from commit e8877c4d7b)

src/nvim/getchar.c

@@ -1959,16 +1959,28 @@ static int handle_mapping(int *keylenp, bool *timedout, int *mapdepth)
       if (mp->m_keys[0] == tb_c1 && (mp->m_mode & local_State)
           && ((mp->m_mode & MODE_LANGMAP) == 0 || typebuf.tb_maplen == 0)) {
         int nomap = nolmaplen;
-        int c2;
+        int modifiers = 0;
         // find the match length of this mapping
         for (mlen = 1; mlen < typebuf.tb_len; mlen++) {
-          c2 = typebuf.tb_buf[typebuf.tb_off + mlen];
+          int c2 = typebuf.tb_buf[typebuf.tb_off + mlen];
           if (nomap > 0) {
+            if (nomap == 2 && c2 == KS_MODIFIER) {
+              modifiers = 1;
+            } else if (nomap == 1 && modifiers == 1) {
+              modifiers = c2;
+            }
             nomap--;
-          } else if (c2 == K_SPECIAL) {
-            nomap = 2;
           } else {
-            LANGMAP_ADJUST(c2, true);
+            if (c2 == K_SPECIAL) {
+              nomap = 2;
+            } else if (merge_modifiers(c2, &modifiers) == c2) {
+              // Only apply 'langmap' if merging modifiers into
+              // the key will not result in another character,
+              // so that 'langmap' behaves consistently in
+              // different terminals and GUIs.
+              LANGMAP_ADJUST(c2, true);
+            }
+            modifiers = 0;
           }
           if (mp->m_keys[mlen] != c2) {
             break;

src/nvim/testdir/test_langmap.vim

@@ -49,6 +49,41 @@ func Test_langmap()
   call feedkeys(';', 'tx')
   call assert_equal(5, col('.'))
 
+  set langmap=RL
+  let g:counter = 0
+  nnoremap L;L <Cmd>let g:counter += 1<CR>
+  nnoremap <C-L> <Cmd>throw 'This mapping shoud not be triggered'<CR>
+
+  " 'langmap' is applied to keys without modifiers when matching a mapping
+  call feedkeys('R;R', 'tx')
+  call assert_equal(1, g:counter)
+  nunmap L;L
+  unlet g:counter
+
+  delete
+  call assert_equal('', getline(1))
+  undo
+  call assert_equal('Hello World', getline(1))
+  " 'langmap' does not change Ctrl-R to Ctrl-L for consistency
+  call feedkeys("\<*C-R>", 'tx')
+  call assert_equal('', getline(1))
+
+  set langmap=6L
+  undo
+  setlocal bufhidden=hide
+  let oldbuf = bufnr()
+  enew
+  call assert_notequal(oldbuf, bufnr())
+  " 'langmap' does not change Ctrl-6 to Ctrl-L for consistency
+  " Ctrl-6 becomes Ctrl-^ after merging the Ctrl modifier
+  call feedkeys("\<*C-6>", 'tx')
+  call assert_equal(oldbuf, bufnr())
+  setlocal bufhidden&
+
+  nunmap <C-L>
+
   set langmap&
   quit!
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab