bug#68493: Got to be a better way to customize c-ts-mode indentation

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Bj=C3=B6rn Lindqvist <[email protected]> writes:

> Den m=C3=A5n 3 aug. 2026 kl 14:46 skrev Tomas Nordin <[email protected]>:
>> Is the following description this bug? Or should I talk more about it in
>> some other or new report?
>>
>> Its about indentation of concatanated strings like this (in a c-buffer)
>>
>> char *lines =3D
>>   "line1\n"
>>   "line2\n"
>>
>> The above is what I "get" with c-mode (in emacs -Q). If I switch over to
>> c-ts-mode and say C-x h and TAB, I get
>>
>> char *lines =3D
>>   "line1\n"
>>     "line2\n"
>>
>> Further literals will align with "line2\n". I would like it to be
>> aligned as with c-mode. Is there a setting for this?
>>
>> This has been observed with
>>
>> GNU Emacs 31.0.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.49, c=
airo version 1.18.4) of 2026-07-02
>
> Hello Tomas,
>
> I can confirm the bug in 32.0.50. However, my c-ts-mode config I
> posted on emacs-devel fixes it:
>
> https://gist.github.com/bjourne/31f53043c72728cb4d8b90feedd0625b
>
> You can take inspiration from that. Specifically, you need to prepend the
> rule ((parent-is "concatenated_string") parent 0) to
> treesit-simple-indent-rules.

Thanks for inspiration. I spent time trying to understand this stuff
better. After that time I don't understand it much better, but maybe a
little bit. With shotgun programming I arrived at the attached patch. It
fixes the problem I reported, and here are two examples where I get what
I want:

    helpexit (argc, argv, 0, 2,
              "Usage: toks [--help] [<delims> [<startchar>]]\n"
              "Read lines from stdin and print tokens.");

and

    char *lines =3D
        "line1\n"
        "line2\n";

The patch was made on top of todays emacs-31. I re-built the whole thing
(patch applied) and will now run with it for some time and see if it
holds.


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diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 5f064716a89..fa09cb21b34 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -503,7 +503,8 @@ c-ts-mode--simple-indent-rules
                                 "enum_specifier"
                                 "union_specifier"
                                 "function_declarator"
-                                "template_declaration")))
+                                "template_declaration"
+                                "concatenated_string")))
             standalone-parent 0)
            ;; This is for the trailing-star stype:  int *
            ;;                                       func()

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