rust-ts-mode: handle invalid rust syntax without signaling

Don't signal an error when encountering invalid rust syntax.  Without
this patch, invalid rust code would prevent a chunk of the buffer from
being highlighted (bug#79272).

* lisp/progmodes/rust-ts-mode.el (rust-ts-mode--fontify-scope):
(rust-ts-mode--fontify-pattern): Avoid calling `string-match-p' on nil
when a node is missing a parent.
* test/lisp/progmodes/rust-ts-mode-resources/font-lock-no-parent.rs:
Rust file that reproduces the issue.
* test/lisp/progmodes/rust-ts-mode-tests.el: Test case to reproduce the
issue.

3 files changed, 19 insertions, 4 deletions

diff --git a/lisp/progmodes/rust-ts-mode.el b/lisp/progmodes/rust-ts-mode.el
index a5c217c0a4b..a98d621af65 100644
--- a/lisp/progmodes/rust-ts-mode.el
+++ b/lisp/progmodes/rust-ts-mode.el
@@ -366,7 +366,8 @@ See https://doc.rust-lang.org/reference/tokens.html#suffixes.")
              tail-p
              (string-match-p
               "\\`\\(?:use_list\\|call_expression\\|use_as_clause\\|use_declaration\\)\\'"
-              (treesit-node-type (treesit-node-parent (treesit-node-parent node)))))
+              (or (treesit-node-type (treesit-node-parent (treesit-node-parent node)))
+                  "no_parent")))
             nil)
            (t 'font-lock-constant-face))))
     (when face
@@ -387,9 +388,9 @@ See https://doc.rust-lang.org/reference/tokens.html#suffixes.")
                        ,(treesit-query-compile 'rust '((identifier) @id
                                                        (shorthand_field_identifier) @id)))))
         (pcase-dolist (`(_name . ,id) captures)
-          (unless (string-match-p "\\`scoped_\\(?:type_\\)?identifier\\'"
-                                  (treesit-node-type
-                                   (treesit-node-parent id)))
+          (unless (string-match-p
+                   "\\`scoped_\\(?:type_\\)?identifier\\'"
+                   (or (treesit-node-type (treesit-node-parent id)) "no_parent"))
             (treesit-fontify-with-override
              (treesit-node-start id) (treesit-node-end id)
              'font-lock-variable-name-face override start end)))))))
diff --git a/test/lisp/progmodes/rust-ts-mode-resources/font-lock-no-parent.rs b/test/lisp/progmodes/rust-ts-mode-resources/font-lock-no-parent.rs
new file mode 100644
index 00000000000..85d0ccc9bf3
--- /dev/null
+++ b/test/lisp/progmodes/rust-ts-mode-resources/font-lock-no-parent.rs
@@ -0,0 +1,7 @@
++// intentionally invalid syntax
++const THING: [u8; 48] = [];
+
+// should recover here and highlight the text below
+trait Foo() {
+// ^ font-lock-keyword-face
+}
diff --git a/test/lisp/progmodes/rust-ts-mode-tests.el b/test/lisp/progmodes/rust-ts-mode-tests.el
index d2e28dcfbd7..32d64260a87 100644
--- a/test/lisp/progmodes/rust-ts-mode-tests.el
+++ b/test/lisp/progmodes/rust-ts-mode-tests.el
@@ -39,6 +39,13 @@
     (ert-font-lock-test-file (ert-resource-file "font-lock-number.rs")
                              'rust-ts-mode)))
 
+(ert-deftest rust-ts-test-no-parent ()
+  (skip-unless (treesit-ready-p 'rust))
+  (let ((treesit-font-lock-level 4)
+        (rust-ts-mode-fontify-number-suffix-as-type t))
+    (ert-font-lock-test-file (ert-resource-file "font-lock-no-parent.rs")
+                             'rust-ts-mode)))
+
 (provide 'rust-ts-mode-tests)
 
 ;;; rust-ts-mode-tests.el ends here