bug#74386: Tree-sitter javascript indentation

[Yuan Fu <casouri@gmail.com>]

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> On Dec 1, 2024, at 2:33 PM, Dmitry Gutov <dmitry@gutov.dev> wrote:
> 
> On 01/12/2024 21:10, Yuan Fu wrote:
>> Ah, I see. That’s a good point, and I definitely prefer the indentation result of parent-bol here. The one produced by standalone-parent is just wrong. What we can do is make standalone-parent ignore “.” when checking for “standaloneness”. And perhaps make it configurable so it’s enabled only for modes that this waiver makes sense (C-like languages excluding C and C++).
> 
> Maybe not by hardcoding this in inside the 'standalone-parent' matcher, but writing this in the indentation rules? Different languages might have differing ASTs for such construct.
> 
> Or if you meant to do a text search, a period might start a method call, but it could also continue a "range" literal in some other language, or some struct initializer (I think?) in C/C++. Also, some languages allow (and style guides suggest) to have the previous at the end of the line, then followed by newline and then the method name.

Not hard-coded, but customizable, like this:

Yuan


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From 301e8a55a14f61258c505a48a973379ac3156079 Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Sun, 1 Dec 2024 18:26:40 -0800
Subject: [PATCH] Standalone predicate POC

---
 lisp/treesit.el | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/lisp/treesit.el b/lisp/treesit.el
index 2acb46ab105..513f58eeffd 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -1597,6 +1597,37 @@ treesit--indent-prev-line-node
       (back-to-indentation)
       (treesit--indent-largest-node-at (point)))))
 
+(defvar treesit-simple-indent-standalone-predicate nil
+  "Function used to determine if a node is \"standalone\".
+
+\"Standalone\" means the node starts on a new line.  For example, if we
+look at the opening bracket, then it's standalone in this case:
+
+    {            <-- Standalone.
+      return 1;
+    }
+
+but not in this case:
+
+    if (true) {  <-- Not standalone.
+      return 1;
+    }
+
+The value of this variable affects the `standalone-parent' indent preset
+for treesit-simple-indent.  If the value is nil, the standlone condition
+is as described.  Some major mode might want to relax the condition a
+little bit, so that it ignores some punctuation like \".\".  For
+example, a Javascript mode might want to consider the method call below
+to be standalone too:
+
+    obj
+    .method(() => {   <-- Consider \".method\" to be standalone,
+      return 1;       <-- so this line anchors on \".method\".
+    });
+
+The value should be a function that takes a node, and return t if it's
+standalone.")
+
 (defvar treesit-simple-indent-presets
   (list (cons 'match
               (lambda
@@ -1736,8 +1767,10 @@ treesit-simple-indent-presets
                   (catch 'term
                     (while parent
                       (goto-char (treesit-node-start parent))
-                      (when (looking-back (rx bol (* whitespace))
-                                          (line-beginning-position))
+                      (when (if (null treesit-simple-indent-standalone-predicate)
+                                (looking-back (rx bol (* whitespace))
+                                              (line-beginning-position))
+                              (funcall parent))
                         (throw 'term (point)))
                       (setq parent (treesit-node-parent parent)))))))
         (cons 'prev-sibling (lambda (node parent bol &rest _)
-- 
2.39.5 (Apple Git-151)