Fix c-ts-mode indentation after if/else (bug#67417)

* lisp/progmodes/c-ts-mode.el:
(c-ts-mode--prev-line-match): New function.
(c-ts-mode--indent-styles): Add a rule for the empty line after
if/else/for/etc.

1 files changed, 16 insertions, 0 deletions

diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 5975057518e..1a7424db5d9 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -355,11 +355,27 @@ PARENT, BOL, ARGS are the same as other anchor functions."
   (apply (alist-get 'standalone-parent treesit-simple-indent-presets)
          parent (treesit-node-parent parent) bol args))
 
+(defun c-ts-mode--prev-line-match (regexp)
+  "An indentation matcher that matches if prev line matches REGEXP."
+  (lambda (_n _p bol &rest _)
+    (save-excursion
+      (goto-char bol)
+      (forward-line -1)
+      (back-to-indentation)
+      (looking-at-p regexp))))
+
 (defun c-ts-mode--indent-styles (mode)
   "Indent rules supported by `c-ts-mode'.
 MODE is either `c' or `cpp'."
   (let ((common
          `((c-ts-mode--for-each-tail-body-matcher prev-line c-ts-mode-indent-offset)
+           ;; If the user types "if (...)" and hit return, they expect
+           ;; the point on the empty line to be indented, this rule
+           ;; does that.
+           ((and no-node
+                 (c-ts-mode--prev-line-match
+                  ,(rx (or "if" "else" "while" "do" "for"))))
+            prev-line c-ts-mode-indent-offset)
 
            ((parent-is "translation_unit") column-0 0)
            ((query "(ERROR (ERROR)) @indent") column-0 0)