bug#46400: [BISECTED] Sporadically breaking newline-indentation in c-mode

[Alan Mackenzie]

Hello, Konstantin.

First of all, thanks for taking the trouble to report this bug, and
thanks even more for taking the diagnosis so far.

On Fri, Feb 12, 2021 at 17:08:19 +0300, Konstantin Kharlamov wrote:
> On Wed, 2021-02-10 at 01:13 +0300, Konstantin Kharlamov wrote:
> > I just bisected it to a commit 

> >     3096437593 CC Mode: introduce a new cache for brace structures.  This
> > fixes bug #45248

> > before this commit I couldn't reproduce it, and on this I reproduce it
> > immediately.

> > CCing the commit author.

> So, what's the plan here? Should I send a revert?

No, please don't do that - that was an essential fix for a performance
bug.

> CC: Alan Mackenzie (I know I already CCed, but I figured they might
> not know they were mentioned if they has mail filters for example,
> since I didn't write the name).

Sorry, I should have got back to you sooner, but I wanted to have
something to show.

I don't think the bug was introduced by the commit you cite, more likely
that commit triggered the bug which was lying in wait elsewhere.

I've been working on this bug for several hours, so far, and have found
that the "c-state-cache" (which records the positions of certain braces,
brackets and parentheses) becomes corrupt while running your `test'
function.  I'm trying to track down where and how this corruption
happens.

Also relevant is that the bug seems to be being triggered by the
apostrophe in

    bar("Couldn't open %s", to);
               ^

..  At least, if I take that apostrophe away, I don't see the bug
symptoms any more.

So, please bear with me some while longer.  I am working on the bug.

-- 
Alan Mackenzie (Nuremberg, Germany).