Rust: Fix QL4QL finding

Author: hvitved

rust/ql/lib/codeql/rust/internal/TypeInference.qll

@@ -2615,8 +2615,8 @@ private Type inferMethodCallTypeSelf(
     path = selfPath and
     not result instanceof TypeParameter
     or
-    exists(TypeParameter tp, TypePath pathToTypeParam, TypePath suffix |
-      impl.targetTypeParameterAt(tp, pathToTypeParam) and
+    exists(TypePath pathToTypeParam, TypePath suffix |
+      impl.targetHasTypeParameterAt(pathToTypeParam) and
       path0 = pathToTypeParam.appendInverse(suffix) and
       result = t0 and
       path = selfPath.append(suffix)

rust/ql/lib/codeql/rust/internal/typeinference/DerefChain.qll

@@ -20,12 +20,13 @@ class DerefImplItemNode extends ImplItemNode {
   Type resolveSelfTypeAt(TypePath path) { result = resolveImplSelfTypeAt(this, path) }
 
   /**
-   * Holds if the target type of the dereference implemention mentions type
-   * parameter `tp` at `path`.
+   * Holds if the target type of the dereference implemention mentions a type
+   * parameter at `path`.
    */
   pragma[nomagic]
-  predicate targetTypeParameterAt(TypeParameter tp, TypePath path) {
-    tp = this.getAssocItem("Target").(TypeAlias).getTypeRepr().(TypeMention).resolveTypeAt(path)
+  predicate targetHasTypeParameterAt(TypePath path) {
+    this.getAssocItem("Target").(TypeAlias).getTypeRepr().(TypeMention).resolveTypeAt(path)
+      instanceof TypeParameter
   }
 
   /** Gets the first type parameter of the type being implemented, if any. */