Rust: Small refactor in TypeMention.qll

Author: hvitved

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

@@ -39,8 +39,8 @@ predicate pathTypeAsTraitAssoc(
 /**
  * Holds if `assoc` is accessed on `tp` in `path`.
  *
- * That is, this is the case when `path` is of the form `<tp as
- * Trait>::AssocType` or `tp::AssocType`; and `AssocType` resolves to `assoc`.
+ * That is, this is the case when `path` is of the form `<tp as Trait>::AssocType`
+ * or `tp::AssocType`; and `AssocType` resolves to `assoc`.
  */
 predicate tpAssociatedType(TypeParam tp, AssocType assoc, Path path) {
   resolvePath(path.getQualifier()) = tp and

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

@@ -699,9 +699,13 @@ class PreTypeMention = PreTypeMention::TypeMention;
 /**
  * Holds if `path` accesses an associated type `alias` from `trait` on a
  * concrete type given by `tm`.
+ *
+ * `implOrTmTrait` is either the mention that resolves to `trait` when `path`
+ * is of the form `<Type as Trait>::AssocType`, or the enclosing `impl` block
+ * when `path` is of the form `Self::AssocType`.
  */
 private predicate pathConcreteTypeAssocType(
-  Path path, PreTypeMention tm, TraitItemNode trait, PreTypeMention tmTrait, TypeAlias alias
+  Path path, PreTypeMention tm, TraitItemNode trait, AstNode implOrTmTrait, TypeAlias alias
 ) {
   exists(Path qualifier |
     qualifier = path.getQualifier() and
@@ -710,19 +714,19 @@ private predicate pathConcreteTypeAssocType(
     // path of the form `<Type as Trait>::AssocType`
     //                    ^^^ tm          ^^^^^^^^^ name
     exists(string name |
-      pathTypeAsTraitAssoc(path, tm, tmTrait, trait, name) and
+      pathTypeAsTraitAssoc(path, tm, implOrTmTrait, trait, name) and
       getTraitAssocType(trait, name) = alias
     )
     or
     // path of the form `Self::AssocType` within an `impl` block
     //                tm ^^^^  ^^^^^^^^^ name
-    exists(ImplItemNode impl |
-      alias = resolvePath(path) and
-      qualifier = impl.getASelfPath() and
-      tm = impl.(Impl).getSelfTy() and
-      trait.getAnAssocItem() = alias and
-      tmTrait = impl.getTraitPath()
-    )
+    implOrTmTrait =
+      any(ImplItemNode impl |
+        alias = resolvePath(path) and
+        qualifier = impl.getASelfPath() and
+        tm = impl.(Impl).getSelfTy() and
+        trait.getAnAssocItem() = alias
+      )
   )
 }
 
@@ -741,21 +745,26 @@ private module PathSatisfiesConstraint =
  */
 private Type getPathConcreteAssocTypeAt(Path path, TypePath typePath) {
   exists(
-    PreTypeMention tm, ImplItemNode impl, TraitItemNode trait, TraitType t, PreTypeMention tmTrait,
+    PreTypeMention tm, ImplItemNode impl, TraitItemNode trait, TraitType t, AstNode implOrTmTrait,
     TypeAlias alias, TypePath path0
   |
-    pathConcreteTypeAssocType(path, tm, trait, tmTrait, alias) and
+    pathConcreteTypeAssocType(path, tm, trait, implOrTmTrait, alias) and
     t = TTrait(trait) and
     PathSatisfiesConstraint::satisfiesConstraintTypeThrough(tm, impl, t, path0, result) and
     path0.isCons(TAssociatedTypeTypeParameter(trait, alias), typePath)
   |
-    tmTrait.getTypeAt(TypePath::nil()) != t
+    implOrTmTrait instanceof Impl
     or
-    not exists(TypePath path1, Type t1 |
-      t1 = impl.getTraitPath().(PreTypeMention).getTypeAt(path1) and
-      not t1 instanceof TypeParameter and
-      t1 != tmTrait.getTypeAt(path1)
-    )
+    // When `path` is of the form `<Type as Trait>::AssocType` we need to check
+    // that `impl` is not more specific than the mentioned trait
+    implOrTmTrait =
+      any(PreTypeMention tmTrait |
+        not exists(TypePath path1, Type t1 |
+          t1 = impl.getTraitPath().(PreTypeMention).getTypeAt(path1) and
+          not t1 instanceof TypeParameter and
+          t1 != tmTrait.getTypeAt(path1)
+        )
+      )
   )
 }