From 5ce35abae6427dac7ac2b147bae8f16adcd8ddff Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Thu, 4 Nov 2021 21:43:05 +0800
Subject: [PATCH] fix(input): never reinterpret unmapped ALT- chrods in
 Terminal mode (#16222)

---
 src/nvim/getchar.c                       |  3 ++-
 test/functional/editor/meta_key_spec.lua | 28 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index a3744067162170..a04914efd5559a 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -1579,7 +1579,8 @@ int vgetc(void)
       // If mappings are enabled (i.e., not Ctrl-v) and the user directly typed
       // something with a meta- or alt- modifier that was not mapped, interpret
       // <M-x> as <Esc>x rather than as an unbound meta keypress. #8213
-      if (!no_mapping && KeyTyped
+      // In Terminal mode, however, this is not desirable. #16220
+      if (!no_mapping && KeyTyped && !(State & TERM_FOCUS)
           && (mod_mask == MOD_MASK_ALT || mod_mask == MOD_MASK_META)) {
         mod_mask = 0;
         ins_char_typebuf(c);
diff --git a/test/functional/editor/meta_key_spec.lua b/test/functional/editor/meta_key_spec.lua
index c2192044090b4a..2280f5bb24cd7c 100644
--- a/test/functional/editor/meta_key_spec.lua
+++ b/test/functional/editor/meta_key_spec.lua
@@ -1,6 +1,8 @@
 local helpers = require('test.functional.helpers')(after_each)
 local clear, feed, insert = helpers.clear, helpers.feed, helpers.insert
 local command = helpers.command
+local exec_lua = helpers.exec_lua
+local eval = helpers.eval
 local expect = helpers.expect
 local funcs = helpers.funcs
 local eq = helpers.eq
@@ -61,4 +63,30 @@ describe('meta-keys #8226 #13042', function()
     feed('u')
     expect('hello')
   end)
+
+  it('ALT/META terminal-mode', function()
+    exec_lua([[
+      _G.input_data = ''
+      vim.api.nvim_open_term(0, { on_input = function(_, _, _, data)
+        _G.input_data = _G.input_data .. vim.fn.strtrans(data)
+      end })
+    ]])
+    -- Mapped ALT-chord behaves as mapped.
+    command('tnoremap <M-l> meta-l')
+    command('tnoremap <A-j> alt-j')
+    feed('i<M-l> xxx <A-j>')
+    eq('meta-l xxx alt-j', exec_lua([[return _G.input_data]]))
+    -- Unmapped ALT-chord is sent to terminal as-is. #16220
+    exec_lua([[_G.input_data = '']])
+    command('tunmap <M-l>')
+    feed('<M-l>')
+    local meta_l_seq = exec_lua([[return _G.input_data]])
+    command('tnoremap <Esc> <C-\\><C-N>')
+    feed('yyy<M-l><A-j>')
+    eq(meta_l_seq .. 'yyy' .. meta_l_seq .. 'alt-j', exec_lua([[return _G.input_data]]))
+    eq('t', eval('mode(1)'))
+    feed('<Esc>j')
+    eq({ 0, 2, 1, 0, }, funcs.getpos('.'))
+    eq('nt', eval('mode(1)'))
+  end)
 end)