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From: Yuan Fu <casouri@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: "Björn Lindqvist" <bjourne@gmail.com>,
	"Emacs Devel" <emacs-devel@gnu.org>
Subject: Re: How does c-ts-mode, tree-sitter indentation, and preprocessor directives work?
Date: Thu, 28 Nov 2024 02:03:44 -0800	[thread overview]
Message-ID: <946BE9A2-08E8-466F-BD0A-39D504B09CE9@gmail.com> (raw)
In-Reply-To: <86plmferwu.fsf@gnu.org>

[-- Attachment #1: Type: text/plain, Size: 2197 bytes --]



> On Nov 27, 2024, at 11:30 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Björn Lindqvist <bjourne@gmail.com>
>> Date: Thu, 28 Nov 2024 00:27:17 +0100
>> 
>> I've been trying to get c-ts-mode to indent like I want, but I'm
>> running into problems related to preprocessor directives.
> 
> Preprocessor directives are difficult because the tree-sitter C/C++
> grammars include only partial support for them.
> 
>> For
>> example, consider a type definition nested in two #ifdefs:
>> 
>>    #ifdef X
>>    #ifdef Y
>>    typedef int foo;
>>    #endif
>>    #endif
>> 
>> Since both the parent and grand parent of the type_definition is a
>> preproc_ifdef no rule matches.
> 
> But if you go back (up) the parent-child hierarchy, you will
> eventually find a node which is not a preproc_SOMETHING, and can go
> from there, no?
> 
>> Another issue is that I want my
>> preprocessor directives kept at column 0, which unfortunately screws
>> up all rules that refer to the parent. E.g.:
>> 
>>    ((parent-is "if_statement") standalone-parent 4)
>> 
>> Doesn't work for
>> 
>>    int main() {
>>        if (true)
>>    #ifdef A
>>            prutt();
>>    #else
>>            fis();
>>    #endif
>>    }
>> 
>> The rule I'd like to express is "take the indent of the closest
>> *indenting* parent and add one indent". That rule would match whether
>> that parent is a "while_statement", "if_statement", "for_statement",
>> etc. You can't express such rules with tree-sitter, can you?
> 
> Not sure, but Yuan will know.

Everything is possible, it’s just elisp. The only problem is how generic you can make the rule. Here’s a POC that only works for this example; specifically, it only works for if statements and #ifdef directives. It should be extendable to for statement, while statement, etc, and maybe other directives too.

Speaking of indent, we need to do something with c-ts-mode’s indentation rules. It’s getting too long and too complex. But I don’t have any great idea at this point. Maybe we can replace the rules with a hand-rolled function so it has more structure, or try nvim’s query approach.

Yuan



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From 25de026b3eb32e7457270cd199fe0902876a2715 Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Thu, 28 Nov 2024 01:51:44 -0800
Subject: [PATCH] Preproc indent POC

---
 lisp/progmodes/c-ts-mode.el | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index c815ee35501..313dcfb5c05 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -435,6 +435,24 @@ c-ts-mode--indent-styles
            ((parent-is "labeled_statement")
             c-ts-mode--standalone-grandparent c-ts-mode-indent-offset)
 
+           ,(let (anchor)
+              (list
+               (lambda (_node parent &rest _)
+                 (let ((anchor-node
+                        (cond
+                         ((treesit-node-match-p parent "preproc_ifdef")
+                          (treesit-node-prev-sibling parent))
+                         ((treesit-node-match-p parent "preproc_else")
+                          (treesit-node-prev-sibling
+                           (treesit-node-parent parent))))))
+                   (when anchor-node
+                     (setq anchor (treesit-node-start anchor-node))
+                     ;; If parent is preproc and previous sibling is
+                     ;; if_statement, set anchor and return t.
+                     (treesit-node-match-p anchor-node "if_statement"))))
+               (lambda (&rest _) anchor)
+               c-ts-mode-indent-offset))
+
            ;; Preproc directives
            ((node-is "preproc") column-0 0)
            ((node-is "#endif") column-0 0)
-- 
2.39.5 (Apple Git-151)


  reply	other threads:[~2024-11-28 10:03 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-11-27 23:27 How does c-ts-mode, tree-sitter indentation, and preprocessor directives work? Björn Lindqvist
2024-11-28  7:30 ` Eli Zaretskii
2024-11-28 10:03   ` Yuan Fu [this message]
2024-11-28 18:30   ` Filippo Argiolas
2024-12-01  6:18     ` Yuan Fu
2024-12-01  8:36       ` Filippo Argiolas
2024-12-01  9:32         ` Yuan Fu

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