feat(defaults): limit syntax cost on CmdwinEnter #15401

Add a new default autocommand to limit syntax highlighting
synchronization in the command window. This refactors the nvim_terminal
autocommand out of main() and into a new init_default_autocmds()
function, which is now part of the startup process and can be further
extended with more default autocommands down the road.

ref #6289 #6399

2 files changed, 30 insertions, 18 deletions

diff --git a/src/nvim/aucmd.c b/src/nvim/aucmd.c
index 32c77fa288..8544a3d2e0 100644
--- a/src/nvim/aucmd.c
+++ b/src/nvim/aucmd.c
@@ -8,6 +8,7 @@
 #include "nvim/ui.h"
 #include "nvim/aucmd.h"
 #include "nvim/eval.h"
+#include "nvim/ex_docmd.h"
 #include "nvim/ex_getln.h"
 #include "nvim/buffer.h"
 
@@ -35,6 +36,30 @@ void do_autocmd_uienter(uint64_t chanid, bool attached)
   recursive = false;
 }
 
+void init_default_autocmds(void)
+{
+  // open terminals when opening files that start with term://
+#define PROTO "term://"
+  do_cmdline_cmd("augroup nvim_terminal");
+  do_cmdline_cmd("autocmd!");
+  do_cmdline_cmd("autocmd BufReadCmd " PROTO "* ++nested "
+                 "if !exists('b:term_title')|call termopen("
+                 // Capture the command string
+                 "matchstr(expand(\"<amatch>\"), "
+                 "'\\c\\m" PROTO "\\%(.\\{-}//\\%(\\d\\+:\\)\\?\\)\\?\\zs.*'), "
+                 // capture the working directory
+                 "{'cwd': expand(get(matchlist(expand(\"<amatch>\"), "
+                 "'\\c\\m" PROTO "\\(.\\{-}\\)//'), 1, ''))})"
+                 "|endif");
+  do_cmdline_cmd("augroup END");
+#undef PROTO
+
+  // limit syntax synchronization in the command window
+  do_cmdline_cmd("augroup nvim_cmdwin");
+  do_cmdline_cmd("autocmd! CmdWinEnter [:>] exe 'syntax sync minlines=1 maxlines='..&cmdwinheight");
+  do_cmdline_cmd("augroup END");
+}
+
 static void focusgained_event(void **argv)
 {
   bool *gainedp = argv[0];
diff --git a/src/nvim/main.c b/src/nvim/main.c
index 9fc82a75af..b73f5aad76 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -309,9 +309,6 @@ int main(int argc, char **argv)
   init_highlight(true, false);  // Default highlight groups.
   TIME_MSG("init highlight");
 
-  init_default_mappings();  // Default mappings.
-  TIME_MSG("init default mappings");
-
   // Set the break level after the terminal is initialized.
   debug_break_level = params.use_debug_break_level;
 
@@ -340,21 +337,11 @@ int main(int argc, char **argv)
     TIME_MSG("initialized screen early for UI");
   }
 
-  // open terminals when opening files that start with term://
-#define PROTO "term://"
-  do_cmdline_cmd("augroup nvim_terminal");
-  do_cmdline_cmd("autocmd!");
-  do_cmdline_cmd("autocmd BufReadCmd " PROTO "* nested "
-                 ":if !exists('b:term_title')|call termopen( "
-                 // Capture the command string
-                 "matchstr(expand(\"<amatch>\"), "
-                 "'\\c\\m" PROTO "\\%(.\\{-}//\\%(\\d\\+:\\)\\?\\)\\?\\zs.*'), "
-                 // capture the working directory
-                 "{'cwd': expand(get(matchlist(expand(\"<amatch>\"), "
-                 "'\\c\\m" PROTO "\\(.\\{-}\\)//'), 1, ''))})"
-                 "|endif");
-  do_cmdline_cmd("augroup END");
-#undef PROTO
+  init_default_mappings();  // Default mappings.
+  TIME_MSG("init default mappings");
+
+  init_default_autocmds();
+  TIME_MSG("init default autocommands");
 
   // Reset 'loadplugins' for "-u NONE" before "--cmd" arguments.
   // Allows for setting 'loadplugins' there.