Make c-ts-mode tests pass even for older tree-sitter libraries

* lisp/progmodes/c-ts-mode.el (c-ts-mode--for-loop-indent-rule):
Use child index instead of field name.

1 files changed, 25 insertions, 14 deletions

diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index dec9411b87c..4cf0c6c405b 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -364,20 +364,31 @@ PARENT is the parent of the current node."
 
 NODE and PARENT as usual."
   (when (treesit-node-match-p parent "for_statement")
-    (pcase (treesit-node-field-name node)
-      ("initializer"
-       ;; Anchor is the opening paren.
-       (cons (treesit-node-start (treesit-node-child parent 1)) 1))
-      ((or "condition" "update")
-       (cons (treesit-node-start (treesit-node-prev-sibling node 'named))
-             0))
-      ("body"
-       (cons (c-ts-common--standalone-parent parent)
-             c-ts-mode-indent-offset))
-      (_ (if (treesit-node-match-p node ")")
-             ;; Anchor is the opening paren.
-             (cons (treesit-node-start (treesit-node-child parent 1)) 0)
-           nil)))))
+    ;; The first version of this function tests for the field name of
+    ;; NODE, which is a lot cleaner.  Alas, older tree-sitter library
+    ;; has a bug in treesit-node-field-name-for-child, which make it
+    ;; give the wrong field name for a child node.
+    (cond
+     ;; Body (Check if NODE is the last child, because when
+     ;; initializer/condition/update is empty, the index of body can
+     ;; change). Eg, for (;;) {...}
+     ((treesit-node-eq node (treesit-node-child parent -1 'named))
+      (cons (c-ts-common--standalone-parent parent)
+            c-ts-mode-indent-offset))
+     ;; Initializer.
+     ((and (treesit-node-check node 'named)
+           (eq (treesit-node-index node 'named) 0 ))
+      ;; Anchor is the opening paren.
+      (cons (treesit-node-start (treesit-node-child parent 1)) 1))
+     ;; Condition and update.
+     ((and (treesit-node-check node 'named)
+           (<= 1 (treesit-node-index node 'named) 2))
+      (cons (treesit-node-start (treesit-node-prev-sibling node 'named))
+            0))
+     ((treesit-node-match-p node ")")
+      ;; Anchor is the opening paren.
+      (cons (treesit-node-start (treesit-node-child parent 1)) 0))
+     (t nil))))
 
 (defvar c-ts-mode--preproc-indent-rules
   `(((node-is "preproc") column-0 0)