Rust: Apply inherent method prioritization inside type inference loop

Author: hvitved

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

@@ -699,7 +699,7 @@ private module CallExprBaseMatchingInput implements MatchingInputSig {
     }
 
     Declaration getTarget() {
-      result = inferMethodCallTarget(this) // mutual recursion; resolving method calls requires resolving types and vice versa
+      result = resolveMethodCallTarget(this) // mutual recursion; resolving method calls requires resolving types and vice versa
       or
       result = CallExprImpl::getResolvedFunction(this)
     }
@@ -1178,14 +1178,14 @@ private predicate methodCandidateTrait(Type type, Trait trait, string name, int
   methodCandidate(type, name, arity, impl)
 }
 
-private module IsInstantiationOfInput implements IsInstantiationOfInputSig<MethodCall> {
-  pragma[nomagic]
-  private predicate isMethodCall(MethodCall mc, Type rootType, string name, int arity) {
-    rootType = mc.getTypeAt(TypePath::nil()) and
-    name = mc.getMethodName() and
-    arity = mc.getNumberOfArguments()
-  }
+pragma[nomagic]
+private predicate isMethodCall(MethodCall mc, Type rootType, string name, int arity) {
+  rootType = mc.getTypeAt(TypePath::nil()) and
+  name = mc.getMethodName() and
+  arity = mc.getNumberOfArguments()
+}
 
+private module IsInstantiationOfInput implements IsInstantiationOfInputSig<MethodCall> {
   pragma[nomagic]
   predicate potentialInstantiationOf(MethodCall mc, TypeAbstraction impl, TypeMention constraint) {
     exists(Type rootType, string name, int arity |
@@ -1334,17 +1334,46 @@ private predicate methodResolutionDependsOnArgument(
   )
 }
 
+/**
+ * Holds if the method call `mc` has no inherent target, i.e., it does not
+ * resolve to a method in an `impl` block for the type of the receiver.
+ */
+pragma[nomagic]
+private predicate methodCallHasNoInherentTarget(MethodCall mc) {
+  exists(Type rootType, string name, int arity |
+    isMethodCall(mc, rootType, name, arity) and
+    forall(Impl impl |
+      methodCandidate(rootType, name, arity, impl) and
+      not impl.hasTrait()
+    |
+      IsInstantiationOf<MethodCall, IsInstantiationOfInput>::isNotInstantiationOf(mc, impl, _)
+    )
+  )
+}
+
+pragma[nomagic]
+private predicate methodCallHasImplCandidate(MethodCall mc, Impl impl) {
+  IsInstantiationOf<MethodCall, IsInstantiationOfInput>::isInstantiationOf(mc, impl, _) and
+  if impl.hasTrait() and not exists(mc.getTrait())
+  then
+    // inherent methods take precedence over trait methods, so only allow
+    // trait methods when there are no matching inherent methods
+    methodCallHasNoInherentTarget(mc)
+  else any()
+}
+
 /** Gets a method from an `impl` block that matches the method call `mc`. */
+pragma[nomagic]
 private Function getMethodFromImpl(MethodCall mc) {
-  exists(Impl impl |
-    IsInstantiationOf<MethodCall, IsInstantiationOfInput>::isInstantiationOf(mc, impl, _) and
-    result = getMethodSuccessor(impl, mc.getMethodName())
+  exists(Impl impl, string name |
+    methodCallHasImplCandidate(mc, impl) and
+    name = mc.getMethodName() and
+    result = getMethodSuccessor(impl, name)
   |
-    not methodResolutionDependsOnArgument(impl, _, _, _, _, _) and
-    result = getMethodSuccessor(impl, mc.getMethodName())
+    not methodResolutionDependsOnArgument(impl, _, _, _, _, _)
     or
     exists(int pos, TypePath path, Type type |
-      methodResolutionDependsOnArgument(impl, mc.getMethodName(), result, pos, path, type) and
+      methodResolutionDependsOnArgument(impl, name, result, pos, path, type) and
       inferType(mc.getPositionalArgument(pos), path) = type
     )
   )
@@ -1356,22 +1385,6 @@ private Function getTraitMethod(ImplTraitReturnType trait, string name) {
   result = getMethodSuccessor(trait.getImplTraitTypeRepr(), name)
 }
 
-/**
- * Gets a method that the method call `mc` resolves to based on type inference,
- * if any.
- */
-private Function inferMethodCallTarget(MethodCall mc) {
-  // The method comes from an `impl` block targeting the type of the receiver.
-  result = getMethodFromImpl(mc)
-  or
-  // The type of the receiver is a type parameter and the method comes from a
-  // trait bound on the type parameter.
-  result = getTypeParameterMethod(mc.getTypeAt(TypePath::nil()), mc.getMethodName())
-  or
-  // The type of the receiver is an `impl Trait` type.
-  result = getTraitMethod(mc.getTypeAt(TypePath::nil()), mc.getMethodName())
-}
-
 cached
 private module Cached {
   private import codeql.rust.internal.CachedStages
@@ -1400,47 +1413,18 @@ private module Cached {
     )
   }
 
-  private predicate isInherentImplFunction(Function f) {
-    f = any(Impl impl | not impl.hasTrait()).(ImplItemNode).getAnAssocItem()
-  }
-
-  private predicate isTraitImplFunction(Function f) {
-    f = any(Impl impl | impl.hasTrait()).(ImplItemNode).getAnAssocItem()
-  }
-
-  private Function resolveMethodCallTargetFrom(MethodCall mc, boolean fromSource) {
-    result = inferMethodCallTarget(mc) and
-    (if result.fromSource() then fromSource = true else fromSource = false) and
-    (
-      // prioritize inherent implementation methods first
-      isInherentImplFunction(result)
-      or
-      not isInherentImplFunction(inferMethodCallTarget(mc)) and
-      (
-        // then trait implementation methods
-        isTraitImplFunction(result)
-        or
-        not isTraitImplFunction(inferMethodCallTarget(mc)) and
-        (
-          // then trait methods with default implementations
-          result.hasBody()
-          or
-          // and finally trait methods without default implementations
-          not inferMethodCallTarget(mc).hasBody()
-        )
-      )
-    )
-  }
-
   /** Gets a method that the method call `mc` resolves to, if any. */
   cached
   Function resolveMethodCallTarget(MethodCall mc) {
-    // Functions in source code also gets extracted as library code, due to
-    // this duplication we prioritize functions from source code.
-    result = resolveMethodCallTargetFrom(mc, true)
+    // The method comes from an `impl` block targeting the type of the receiver.
+    result = getMethodFromImpl(mc)
+    or
+    // The type of the receiver is a type parameter and the method comes from a
+    // trait bound on the type parameter.
+    result = getTypeParameterMethod(mc.getTypeAt(TypePath::nil()), mc.getMethodName())
     or
-    not exists(resolveMethodCallTargetFrom(mc, true)) and
-    result = resolveMethodCallTargetFrom(mc, false)
+    // The type of the receiver is an `impl Trait` type.
+    result = getTraitMethod(mc.getTypeAt(TypePath::nil()), mc.getMethodName())
   }
 
   pragma[inline]

rust/ql/test/library-tests/dataflow/sources/CONSISTENCY/PathResolutionConsistency.expected

@@ -10,6 +10,9 @@ multipleCallTargets
 | test.rs:168:26:168:111 | ...::_print(...) |
 | test.rs:178:30:178:68 | ...::_print(...) |
 | test.rs:187:26:187:105 | ...::_print(...) |
+| test.rs:228:22:228:72 | ... .read_to_string(...) |
+| test.rs:482:22:482:50 | file.read_to_end(...) |
+| test.rs:488:22:488:53 | file.read_to_string(...) |
 | test.rs:609:18:609:38 | ...::_print(...) |
 | test.rs:614:18:614:45 | ...::_print(...) |
 | test.rs:618:25:618:49 | address.to_socket_addrs() |

rust/ql/test/library-tests/type-inference/CONSISTENCY/PathResolutionConsistency.expected

@@ -1,9 +1,9 @@
 multipleCallTargets
 | dereference.rs:61:15:61:24 | e1.deref() |
-| main.rs:1963:13:1963:31 | ...::from(...) |
-| main.rs:1964:13:1964:31 | ...::from(...) |
-| main.rs:1965:13:1965:31 | ...::from(...) |
-| main.rs:1970:13:1970:31 | ...::from(...) |
-| main.rs:1971:13:1971:31 | ...::from(...) |
-| main.rs:1972:13:1972:31 | ...::from(...) |
-| main.rs:2006:21:2006:43 | ...::from(...) |
+| main.rs:2032:13:2032:31 | ...::from(...) |
+| main.rs:2033:13:2033:31 | ...::from(...) |
+| main.rs:2034:13:2034:31 | ...::from(...) |
+| main.rs:2040:13:2040:31 | ...::from(...) |
+| main.rs:2041:13:2041:31 | ...::from(...) |
+| main.rs:2042:13:2042:31 | ...::from(...) |
+| main.rs:2078:21:2078:43 | ...::from(...) |