Rust: Query for missing elements.

rust/ql/src/queries/diagnostics/MissingElements.ql

@@ -0,0 +1,26 @@
+/**
+ * @name Missing Elements
+ * @description List all elements that weren't extracted due to unimplemented features or parse errors.
+ * @kind diagnostic
+ * @id rust/diagnostics/missing-elements
+ */
+
+import rust
+
+query predicate listUnimplemented(AstNode n, string msg) {
+  // not extracted yet
+  n instanceof Unimplemented and
+  msg = "Not yet implemented."
+}
+
+query predicate listMissingExpr(Expr e, string msg) {
+  // gaps in the AST due to parse errors
+  e instanceof MissingExpr and
+  msg = "Missing expression."
+}
+
+query predicate listMissingPat(Pat p, string msg) {
+  // gaps in the AST due to parse errors
+  p instanceof MissingPat and
+  msg = "Missing pattern."
+}