Rust: Take internal IDs of a smaller class

Author: paldepind

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

@@ -69,11 +69,18 @@ private module Input1 implements InputSig1<Location> {
     apos.asMethodTypeArgumentPosition() = ppos.asTypeParam().getPosition()
   }
 
+  private import codeql.rust.elements.internal.generated.Synth
+
+  private class TTypeParameterAstNode = Synth::TTypeParam or Synth::TTrait;
+
+  /** An `AstNode` that might correspond to a `TypeParameter`. */
+  private class TypeParameterAstNode extends AstNode, TTypeParameterAstNode { }
+
   private predicate id(Raw::AstNode x, Raw::AstNode y) { x = y }
 
   private predicate idOfRaw(Raw::AstNode x, int y) = equivalenceRelation(id/2)(x, y)
 
-  private int idOf(AstNode node) { idOfRaw(Synth::convertAstNodeToRaw(node), result) }
+  private int idOf(TypeParameterAstNode node) { idOfRaw(Synth::convertAstNodeToRaw(node), result) }
 
   int getTypeParameterId(TypeParameter tp) {
     tp =
@@ -83,7 +90,7 @@ private module Input1 implements InputSig1<Location> {
         id = 0
         or
         kind = 1 and
-        exists(AstNode node | id = idOf(node) |
+        exists(TypeParameterAstNode node | id = idOf(node) |
           node = tp0.(TypeParamTypeParameter).getTypeParam() or
           node = tp0.(SelfTypeParameter).getTrait()
         )