Rust: Disambiguate types inferred from trait bounds

Author: hvitved

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

@@ -13,68 +13,105 @@ private import TypeMention
 private import TypeInference
 private import FunctionType
 
-pragma[nomagic]
-private Type resolveNonTypeParameterTypeAt(TypeMention tm, TypePath path) {
-  result = tm.getTypeAt(path) and
-  not result instanceof TypeParameter
-}
+private signature Type resolveTypeMentionAtSig(AstNode tm, TypePath path);
 
-bindingset[t1, t2]
-private predicate typeMentionEqual(TypeMention t1, TypeMention t2) {
-  forex(TypePath path, Type type | resolveNonTypeParameterTypeAt(t1, path) = type |
-    resolveNonTypeParameterTypeAt(t2, path) = type
-  )
-}
+/**
+ * Provides logic for identifying sibling implementations, parameterized over
+ * how to resolve type mentions (`PreTypeMention` vs. `TypeMention`).
+ */
+private module MkSiblingImpls<resolveTypeMentionAtSig/2 resolveTypeMentionAt> {
+  pragma[nomagic]
+  private Type resolveNonTypeParameterTypeAt(AstNode tm, TypePath path) {
+    result = resolveTypeMentionAt(tm, path) and
+    not result instanceof TypeParameter
+  }
 
-pragma[nomagic]
-private predicate implSiblingCandidate(
-  Impl impl, TraitItemNode trait, Type rootType, TypeMention selfTy
-) {
-  trait = impl.(ImplItemNode).resolveTraitTy() and
-  selfTy = impl.getSelfTy() and
-  rootType = selfTy.getType()
+  bindingset[t1, t2]
+  private predicate typeMentionEqual(AstNode t1, AstNode t2) {
+    forex(TypePath path, Type type | resolveNonTypeParameterTypeAt(t1, path) = type |
+      resolveNonTypeParameterTypeAt(t2, path) = type
+    )
+  }
+
+  pragma[nomagic]
+  private predicate implSiblingCandidate(
+    Impl impl, TraitItemNode trait, Type rootType, AstNode selfTy
+  ) {
+    trait = impl.(ImplItemNode).resolveTraitTy() and
+    selfTy = impl.getSelfTy() and
+    rootType = resolveTypeMentionAt(selfTy, TypePath::nil())
+  }
+
+  pragma[nomagic]
+  private predicate blanketImplSiblingCandidate(ImplItemNode impl, Trait trait) {
+    impl.isBlanketImplementation() and
+    trait = impl.resolveTraitTy()
+  }
+
+  /**
+   * Holds if `impl1` and `impl2` are sibling implementations of `trait`. We
+   * consider implementations to be siblings if they implement the same trait for
+   * the same type. In that case `Self` is the same type in both implementations,
+   * and method calls to the implementations cannot be resolved unambiguously
+   * based only on the receiver type.
+   */
+  pragma[inline]
+  predicate implSiblings(TraitItemNode trait, Impl impl1, Impl impl2) {
+    impl1 != impl2 and
+    (
+      exists(Type rootType, AstNode selfTy1, AstNode selfTy2 |
+        implSiblingCandidate(impl1, trait, rootType, selfTy1) and
+        implSiblingCandidate(impl2, trait, rootType, selfTy2) and
+        // In principle the second conjunct below should be superfluous, but we still
+        // have ill-formed type mentions for types that we don't understand. For
+        // those checking both directions restricts further. Note also that we check
+        // syntactic equality, whereas equality up to renaming would be more
+        // correct.
+        typeMentionEqual(selfTy1, selfTy2) and
+        typeMentionEqual(selfTy2, selfTy1)
+      )
+      or
+      blanketImplSiblingCandidate(impl1, trait) and
+      blanketImplSiblingCandidate(impl2, trait)
+    )
+  }
+
+  /**
+   * Holds if `impl` is an implementation of `trait` and if another implementation
+   * exists for the same type.
+   */
+  pragma[nomagic]
+  predicate implHasSibling(ImplItemNode impl, Trait trait) { implSiblings(trait, impl, _) }
+
+  pragma[nomagic]
+  predicate implHasAmbiguousSiblingAt(ImplItemNode impl, Trait trait, TypePath path) {
+    exists(ImplItemNode impl2, Type t1, Type t2 |
+      implSiblings(trait, impl, impl2) and
+      t1 = resolveTypeMentionAt(impl.getTraitPath(), path) and
+      t2 = resolveTypeMentionAt(impl2.getTraitPath(), path) and
+      t1 != t2
+    |
+      not t1 instanceof TypeParameter or
+      not t2 instanceof TypeParameter
+    )
+  }
 }
 
-pragma[nomagic]
-private predicate blanketImplSiblingCandidate(ImplItemNode impl, Trait trait) {
-  impl.isBlanketImplementation() and
-  trait = impl.resolveTraitTy()
+private Type resolvePreTypeMention(AstNode tm, TypePath path) {
+  result = tm.(PreTypeMention).getTypeAt(path)
 }
 
-/**
- * Holds if `impl1` and `impl2` are a sibling implementations of `trait`. We
- * consider implementations to be siblings if they implement the same trait for
- * the same type. In that case `Self` is the same type in both implementations,
- * and method calls to the implementations cannot be resolved unambiguously
- * based only on the receiver type.
- */
-pragma[inline]
-private predicate implSiblings(TraitItemNode trait, Impl impl1, Impl impl2) {
-  impl1 != impl2 and
-  (
-    exists(Type rootType, TypeMention selfTy1, TypeMention selfTy2 |
-      implSiblingCandidate(impl1, trait, rootType, selfTy1) and
-      implSiblingCandidate(impl2, trait, rootType, selfTy2) and
-      // In principle the second conjunct below should be superflous, but we still
-      // have ill-formed type mentions for types that we don't understand. For
-      // those checking both directions restricts further. Note also that we check
-      // syntactic equality, whereas equality up to renaming would be more
-      // correct.
-      typeMentionEqual(selfTy1, selfTy2) and
-      typeMentionEqual(selfTy2, selfTy1)
-    )
-    or
-    blanketImplSiblingCandidate(impl1, trait) and
-    blanketImplSiblingCandidate(impl2, trait)
-  )
+private module PreSiblingImpls = MkSiblingImpls<resolvePreTypeMention/2>;
+
+predicate preImplHasAmbiguousSiblingAt = PreSiblingImpls::implHasAmbiguousSiblingAt/3;
+
+private Type resolveTypeMention(AstNode tm, TypePath path) {
+  result = tm.(TypeMention).getTypeAt(path)
 }
 
-/**
- * Holds if `impl` is an implementation of `trait` and if another implementation
- * exists for the same type.
- */
-pragma[nomagic]
-private predicate implHasSibling(ImplItemNode impl, Trait trait) { implSiblings(trait, impl, _) }
+private module SiblingImpls = MkSiblingImpls<resolveTypeMention/2>;
+
+import SiblingImpls
 
 /**
  * Holds if `f` is a function declared inside `trait`, and the type of `f` at