vim-patch:8.1.1591: on error garbage collection may free memory in use

Problem:    On error garbage collection may free memory in use.
Solution:   Reset may_garbage_collect when evaluating expression mapping.
            Add tests. (Ozaki Kiichi, closes vim/vim#4579)
vim/vim@7d491c4

src/nvim/getchar.c

@@ -2044,14 +2044,19 @@ static int vgetorpeek(bool advance)
              */
             if (mp->m_expr) {
               int save_vgetc_busy = vgetc_busy;
+              const bool save_may_garbage_collect = may_garbage_collect;
 
               vgetc_busy = 0;
+              may_garbage_collect = false;
+
               save_m_keys = vim_strsave(mp->m_keys);
               save_m_str = vim_strsave(mp->m_str);
               s = eval_map_expr(save_m_str, NUL);
               vgetc_busy = save_vgetc_busy;
-            } else
+              may_garbage_collect = save_may_garbage_collect;
+            } else {
               s = mp->m_str;
+            }
 
             /*
              * Insert the 'to' part in the typebuf.tb_buf.

src/nvim/testdir/test_mapping.vim

@@ -391,6 +391,42 @@ func Test_motionforce_omap()
   delfunc GetCommand
 endfunc
 
+func Test_error_in_map_expr()
+  if !has('terminal') || (has('win32') && has('gui_running'))
+    throw 'Skipped: cannot run Vim in a terminal window'
+  endif
+
+  let lines =<< trim [CODE]
+  func Func()
+    " fail to create list
+    let x = [
+  endfunc
+  nmap <expr> ! Func()
+  set updatetime=50
+  [CODE]
+  call writefile(lines, 'Xtest.vim')
+
+  let buf = term_start(GetVimCommandClean() .. ' -S Xtest.vim', {'term_rows': 8})
+  let job = term_getjob(buf)
+  call WaitForAssert({-> assert_notequal('', term_getline(buf, 8))})
+
+  " GC must not run during map-expr processing, which can make Vim crash.
+  call term_sendkeys(buf, '!')
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "\<CR>")
+  call term_wait(buf, 100)
+  call assert_equal('run', job_status(job))
+
+  call term_sendkeys(buf, ":qall!\<CR>")
+  call WaitFor({-> job_status(job) ==# 'dead'})
+  if has('unix')
+    call assert_equal('', job_info(job).termsig)
+  endif
+
+  call delete('Xtest.vim')
+  exe buf .. 'bwipe!'
+endfunc
+
 " Test for mapping errors
 func Test_map_error()
   call assert_fails('unmap', 'E474:')

src/nvim/testdir/test_timers.vim

@@ -340,6 +340,41 @@ func Test_nocatch_garbage_collect()
   delfunc FeedChar
 endfunc
 
+func Test_error_in_timer_callback()
+  if !has('terminal') || (has('win32') && has('gui_running'))
+    throw 'Skipped: cannot run Vim in a terminal window'
+  endif
+
+  let lines =<< trim [CODE]
+  func Func(timer)
+    " fail to create list
+    let x = [
+  endfunc
+  set updatetime=50
+  call timer_start(1, 'Func')
+  [CODE]
+  call writefile(lines, 'Xtest.vim')
+
+  let buf = term_start(GetVimCommandClean() .. ' -S Xtest.vim', {'term_rows': 8})
+  let job = term_getjob(buf)
+  call WaitForAssert({-> assert_notequal('', term_getline(buf, 8))})
+
+  " GC must not run during timer callback, which can make Vim crash.
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "\<CR>")
+  call term_wait(buf, 100)
+  call assert_equal('run', job_status(job))
+
+  call term_sendkeys(buf, ":qall!\<CR>")
+  call WaitFor({-> job_status(job) ==# 'dead'})
+  if has('unix')
+    call assert_equal('', job_info(job).termsig)
+  endif
+
+  call delete('Xtest.vim')
+  exe buf .. 'bwipe!'
+endfunc
+
 func Test_timer_invalid_callback()
   call assert_fails('call timer_start(0, "0")', 'E921')
 endfunc

src/nvim/testdir/test_vimscript.vim

@@ -1409,7 +1409,7 @@ func Test_compound_assignment_operators()
     let @/ = ''
 endfunc
 
-func! Test_funccall_garbage_collect()
+func Test_funccall_garbage_collect()
     func Func(x, ...)
         call add(a:x, a:000)
     endfunc