Rust: Split getFunctionReturnPos into two predicates

Author: paldepind

rust/ql/lib/codeql/rust/elements/internal/ImplTraitTypeReprImpl.qll

@@ -23,10 +23,14 @@ module Impl {
    * ```
    */
   class ImplTraitTypeRepr extends Generated::ImplTraitTypeRepr {
-    /**
-     * Gets the function for which this impl trait type occurs in the return
-     * type, if any.
-     */
-    Function getFunctionReturnPos() { this.getParentNode*() = result.getRetType().getTypeRepr() }
+    /** Gets the function for which this impl trait type occurs, if any. */
+    Function getFunction() {
+      this.getParentNode*() = [result.getRetType().getTypeRepr(), result.getAParam().getTypeRepr()]
+    }
+
+    /** Holds if this impl trait type occurs in the return type of a function. */
+    predicate isInReturnPos() {
+      this.getParentNode*() = this.getFunction().getRetType().getTypeRepr()
+    }
   }
 }

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

@@ -60,7 +60,8 @@ newtype TType =
   TSliceTypeParameter()
 
 predicate implTraitTypeParam(ImplTraitTypeRepr implTrait, int i, TypeParam tp) {
-  tp = implTrait.getFunctionReturnPos().getGenericParamList().getTypeParam(i) and
+  implTrait.isInReturnPos() and
+  tp = implTrait.getFunction().getGenericParamList().getTypeParam(i) and
   // Only include type parameters of the function that occur inside the impl
   // trait type.
   exists(Path path | path.getParentNode*() = implTrait and resolvePath(path) = tp)
@@ -317,7 +318,7 @@ class DynTraitType extends Type, TDynTraitType {
 class ImplTraitReturnType extends ImplTraitType {
   private Function function;
 
-  ImplTraitReturnType() { function = impl.getFunctionReturnPos() }
+  ImplTraitReturnType() { impl.isInReturnPos() and function = impl.getFunction() }
 
   override Function getFunction() { result = function }
 }