Editing C source files has been slower since `3fe5ff6`

[chabulhwi]

Describe your issue

After 21166d118449ea3ca07334748453bf8151704b25, it became much slower to add or edit declarations of array variables with initializers in C.

commit 21166d118449ea3ca07334748453bf8151704b25
Author: Henrik Lissner <git@henrik.io>
Date:   Tue Jun 23 19:09:38 2026 -0400

    bump: sources/doom+
    
    doomemacs/modules@5a44cf7bdb74 -> doomemacs/modules@4fcb2b1a5063

Steps to reproduce

1. In the ~/.config/emacs directory, run git checkout 21166d1 and reinstall Doom Emacs.
2. Open Doom Emacs and try writing the following C code by hand. The input lag should be noticeable.

int main(void)
{
	int a = 10;

	int b[] = {1, 2, 3};

	int c[] = {4, 5, 6, 7};

	int d[] = {8, 9, 10, 11, 12};

	double e[] = {1.2, 3.4, 5.6};

	return 0;
}

3. In the previous directory, run git checkout HEAD~1 and reinstall Doom Emacs.
4. Try writing the C code above again. Typing would be much faster than before.

System information

doom-info.txt

Disclosures

• This issue was written with/by AI.

[hlissner]

I'm not experiencing any difference (or any slowness at all) between the two commits.

Your doom-info also says you're on ab8e54bfc, which is nearly 2 months old?

It also says you have lsp-enable-on-type-formatting enabled (in $DOOMDIR/custom.el). Try disabling this, as it causes lsp-mode to apply formatting as you type.

Nothing else comes to mind.

[hlissner]

Try profiling the issue.

[chabulhwi]

Your doom-info also says you're on doomemacs/core@ab8e54b, which is nearly 2 months old?

ab8e54bfc7f78160dc2884c719edf80ad0a622cb is the commit right before 21166d118449ea3ca07334748453bf8151704b25.

chabulhwi@desktop ~/.c/emacs (master)> git log -2 21166d1
commit 21166d118449ea3ca07334748453bf8151704b25
Author: Henrik Lissner <git@henrik.io>
Date:   Tue Jun 23 19:09:38 2026 -0400

    bump: sources/doom+
    
    doomemacs/modules@5a44cf7bdb74 -> doomemacs/modules@4fcb2b1a5063

commit ab8e54bfc7f78160dc2884c719edf80ad0a622cb
Author: Henrik Lissner <git@henrik.io>
Date:   Tue Jun 23 23:57:07 2026 -0400

    fix(lib): doom/info: envvar file detector

It also says you have lsp-enable-on-type-formatting enabled (in $DOOMDIR/custom.el). Try disabling this, as it causes lsp-mode to apply formatting as you type.

Sorry, I forgot to tell you that I'd moved all of my Doom configuration files to ~/Projects/doom-config while I used git bisect to pinpoint the commit that caused typing lag. I've restored these files afterward.

[chabulhwi]

Try profiling the issue.

Here's the report from the profiler: https://paste.sr.ht/~chabulhwi/a8d0b611d9d18245f15f1a75a1d50a0a5b9d21ac.

[hlissner]

It's a tree. You can expand each function call stack by move the cursor over it and pressing tab.

Do that to drill down into the top functions in the profiler output to see where it's really spending most of its time.

[chabulhwi]

I've modified my previous comment.

[hlissner]

Does disabling smartparens-mode speed it up? I.e M-x smartparens-mode in the C buffer.

[chabulhwi]

No, not really.

[chabulhwi]

Using git bisect, I've found that 3fe5ff6 caused typing lag.

commit 3fe5ff6cd9cc1c5887f7ecf8653cbcd85a0498d1
Author: Henrik Lissner <git@henrik.io>
Date:   Tue Jun 23 18:41:41 2026 -0400

    bump: :ui
    
    dgutov/diff-hl@902d082d70b9 -> dgutov/diff-hl@2f1623d98a29
    jdtsmith/ultra-scroll@f38653053b5c -> jdtsmith/ultra-scroll@5be267d2d92c
    seagle0128/doom-modeline@0b660ed93a18 -> seagle0128/doom-modeline@4e8df6362ea0