ex_getln: Check prev_prompt_errors before running redrawcmdline

Otherwise there will be infinite recursion and shortly a crash. Running 
redrawcmdline recursively occurs under color_cmdline_error label.

2 files changed, 22 insertions, 6 deletions

diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 13bae4dadc..4be0dd0e0d 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -2364,6 +2364,12 @@ static bool color_cmdline(void)
   bool dgc_ret = true;
   bool tl_ret = true;
 
+  if (ccline.prompt_id != prev_prompt_id) {
+    prev_prompt_errors = 0;
+    prev_prompt_id = ccline.prompt_id;
+  } else if (prev_prompt_errors >= MAX_CB_ERRORS) {
+    goto color_cmdline_end;
+  }
   if (ccline.highlight_callback.type != kCallbackNone) {
     // Currently this should only happen while processing input() prompts.
     assert(ccline.input_fn);
@@ -2392,12 +2398,6 @@ static bool color_cmdline(void)
   if (color_cb.type == kCallbackNone) {
     goto color_cmdline_end;
   }
-  if (ccline.prompt_id != prev_prompt_id) {
-    prev_prompt_errors = 0;
-    prev_prompt_id = ccline.prompt_id;
-  } else if (prev_prompt_errors >= MAX_CB_ERRORS) {
-    goto color_cmdline_end;
-  }
   if (ccline.cmdbuff[ccline.cmdlen] != NUL) {
     arg_allocated = true;
     arg.vval.v_string = xmemdupz((const char *)ccline.cmdbuff,
diff --git a/test/functional/ui/cmdline_highlight_spec.lua b/test/functional/ui/cmdline_highlight_spec.lua
index 6698ced596..e12961039a 100644
--- a/test/functional/ui/cmdline_highlight_spec.lua
+++ b/test/functional/ui/cmdline_highlight_spec.lua
@@ -527,6 +527,22 @@ describe('Ex commands coloring support', function()
     eq('\nError detected while processing :\nE605: Exception not caught: 42',
        meths.command_output('messages'))
   end)
+  it('errors out when failing to get callback', function()
+    meths.set_var('Nvim_color_cmdline', 42)
+    feed(':#')
+    screen:expect([[
+      {EOB:~                                       }|
+      {EOB:~                                       }|
+      {EOB:~                                       }|
+      :                                       |
+      {ERR:E5408: Unable to get Nvim_color_cmdline }|
+      {ERR:callback from g:: Vim:E6000: Argument is}|
+      {ERR: not a function or function name}        |
+      :#^                                      |
+    ]])
+  end)
+end)
+describe('Expressions coloring support', function()
 end)
 
 -- TODO Specifically test for coloring in cmdline and expr modes