emacs-29 28dd602138 1/2: Fix c-ts-mode indentation for 2nd line in block comment (bug#60270)

[Yuan Fu]

branch: emacs-29
commit 28dd60213846a04d3f8c4006bd4ec252bd883ed0
Author: Yuan Fu <casouri@gmail.com>
Commit: Yuan Fu <casouri@gmail.com>

    Fix c-ts-mode indentation for 2nd line in block comment (bug#60270)
    
    If the first line is "/*" or "/*   ", indent like this:
    
    /*
       aaa
    
    If the first line is "/*   some text", indent like this:
    
    /*   some text
         aaa
    
    * lisp/progmodes/c-ts-mode.el (c-ts-mode--indent-styles):
    (c-ts-mode--looking-at-star): Minor refactor.
    (c-ts-mode--comment-2nd-line-matcher)
    (c-ts-mode--comment-2nd-line-anchor): New functions.
    * lisp/treesit.el (treesit-simple-indent-presets):
    prev-adaptive-prefix doesn't handle the comment-start-skip case (i.e,
    2nd line) anymore.  (Handled by the new matcher.)
---
 lisp/progmodes/c-ts-mode.el | 38 +++++++++++++++++++++++++++++++++-----
 lisp/treesit.el             | 25 +++++++++++--------------
 2 files changed, 44 insertions(+), 19 deletions(-)

diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 772b259d59..898b89b9fc 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -122,6 +122,9 @@ MODE is either `c' or `cpp'."
            ((node-is "else") parent-bol 0)
            ((node-is "case") parent-bol 0)
            ((node-is "preproc_arg") no-indent)
+           (c-ts-mode--comment-2nd-line-matcher
+            c-ts-mode--comment-2nd-line-anchor
+            1)
            ((and (parent-is "comment") c-ts-mode--looking-at-star)
             c-ts-mode--comment-start-after-first-star -1)
            ((parent-is "comment") prev-adaptive-prefix 0)
@@ -227,11 +230,8 @@ beginning of grandparent."
 
 (defun c-ts-mode--looking-at-star (_n _p bol &rest _)
   "A tree-sitter simple indent matcher.
-Matches if there is a \"*\" after point (ignoring whitespace in
-between)."
-  (save-excursion
-    (goto-char bol)
-    (looking-at (rx (* (syntax whitespace)) "*"))))
+Matches if there is a \"*\" after BOL."
+  (eq (char-after bol) ?*))
 
 (defun c-ts-mode--comment-start-after-first-star (_n parent &rest _)
   "A tree-sitter simple indent anchor.
@@ -243,6 +243,34 @@ Assumes PARENT is a comment node."
         (match-end 0)
       (point))))
 
+(defun c-ts-mode--comment-2nd-line-matcher (_n parent &rest _)
+  "Matches if point is at the second line of a block comment.
+PARENT should be a comment node."
+  (save-excursion
+    (forward-line -1)
+    (back-to-indentation)
+    (eq (point) (treesit-node-start parent))))
+
+(defun c-ts-mode--comment-2nd-line-anchor (&rest _)
+  "Return appropriate anchor for the second line of a comment.
+
+If the first line is /* alone, return the position right after
+the star; if the first line is /* followed by some text, return
+the position right before the text minus 1.
+
+Use an offset of 1 with this anchor."
+  (save-excursion
+    (forward-line -1)
+    (back-to-indentation)
+    (when (looking-at comment-start-skip)
+      (goto-char (match-end 0))
+      (if (looking-at (rx (* (or " " "\t")) eol))
+          ;; Only /* at the first line.
+          (progn (skip-chars-backward " \t")
+                 (point))
+        ;; There is something after /* at the first line.
+        (1- (point))))))
+
 ;;; Font-lock
 
 (defvar c-ts-mode--preproc-keywords
diff --git a/lisp/treesit.el b/lisp/treesit.el
index 7a604121c4..5b30635446 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -1143,20 +1143,17 @@ See `treesit-simple-indent-presets'.")
                   (point))))
         (cons 'prev-adaptive-prefix
               (lambda (_n parent &rest _)
-                (save-excursion
-                  (re-search-backward
-                   (rx (not (or " " "\t" "\n"))) nil t)
-                  (beginning-of-line)
-                  (and (>= (point) (treesit-node-start parent))
-                       ;; `adaptive-fill-regexp' will not match "/*",
-                       ;; so we need to also try `comment-start-skip'.
-                       (or (and adaptive-fill-regexp
-                                (looking-at adaptive-fill-regexp)
-                                (> (- (match-end 0) (match-beginning 0)) 0)
-                                (match-end 0))
-                           (and comment-start-skip
-                                (looking-at comment-start-skip)
-                                (match-end 0)))))))
+                (let ((comment-start-bol
+                       (save-excursion
+                         (goto-char (treesit-node-start parent))
+                         (line-beginning-position))))
+                  (save-excursion
+                    (forward-line -1)
+                    (and (>= (point) comment-start-bol)
+                         adaptive-fill-regexp
+                         (looking-at adaptive-fill-regexp)
+                         (> (match-end 0) (match-beginning 0))
+                         (match-end 0))))))
         ;; TODO: Document.
         (cons 'grand-parent
               (lambda (_n parent &rest _)