inccommand: auto-disable if folding is slow #9568

Fixes #9557

src/nvim/ex_cmds.c

@@ -4135,7 +4135,7 @@ skip:
   buf_T *preview_buf = NULL;
   size_t subsize = preview_lines.subresults.size;
   if (preview && !aborting()) {
-    if (got_quit) {  // Substitution is too slow, disable 'inccommand'.
+    if (got_quit || profile_passed_limit(timeout)) {  // Too slow, disable.
       set_string_option_direct((char_u *)"icm", -1, (char_u *)"", OPT_FREE,
                                SID_NONE);
     } else if (*p_icm != NUL &&  pat != NULL) {

test/functional/ui/inccommand_spec.lua

@@ -1151,6 +1151,39 @@ describe(":substitute, inccommand=split", function()
     eq("split", eval("&inccommand"))
   end)
 
+  it("deactivates if 'foldexpr' is slow #9557", function()
+    insert([[
+      a
+      a
+      a
+      a
+      a
+      a
+      a
+      a
+    ]])
+    source([[
+      function! Slowfold(lnum)
+        sleep 5m
+        return a:lnum % 3
+      endfun
+    ]])
+    command('set redrawtime=1 inccommand=split')
+    command('set foldmethod=expr foldexpr=Slowfold(v:lnum)')
+    feed(':%s/a/bcdef')
+
+    -- Assert that 'inccommand' is DISABLED in cmdline mode.
+    retry(nil, nil, function()
+      eq('', eval('&inccommand'))
+    end)
+
+    -- Assert that 'inccommand' is again ENABLED after leaving cmdline mode.
+    feed([[<C-\><C-N>]])
+    retry(nil, nil, function()
+      eq('split', eval('&inccommand'))
+    end)
+  end)
+
   it("clears preview if non-previewable command is edited #5585", function()
     -- Put a non-previewable command in history.
     feed_command("echo 'foo'")