[ConstraintSystem] A few improvements to key path handling and diagnostics

include/swift/Sema/CSFix.h

@@ -393,10 +393,6 @@ enum class FixKind : uint8_t {
   /// is marked as `inout`.
   AllowConversionThroughInOut,
 
-  /// Ignore either capability (read/write) or type mismatch in conversion
-  /// between two key path types.
-  IgnoreKeyPathContextualMismatch,
-
   /// Ignore a type mismatch between deduced element type and externally
   /// imposed one.
   IgnoreCollectionElementContextualMismatch,
@@ -1167,36 +1163,6 @@ class GenericArgumentsMismatch final
   }
 };
 
-/// Detect situations where key path doesn't have capability required
-/// by the context e.g. read-only vs. writable, or either root or value
-/// types are incorrect e.g.
-///
-/// ```swift
-/// struct S { let foo: Int }
-/// let _: WritableKeyPath<S, Int> = \.foo
-/// ```
-///
-/// Here context requires a writable key path but `foo` property is
-/// read-only.
-class KeyPathContextualMismatch final : public ContextualMismatch {
-  KeyPathContextualMismatch(ConstraintSystem &cs, Type lhs, Type rhs,
-                            ConstraintLocator *locator)
-      : ContextualMismatch(cs, FixKind::IgnoreKeyPathContextualMismatch, lhs,
-                           rhs, locator) {}
-
-public:
-  std::string getName() const override {
-    return "fix key path contextual mismatch";
-  }
-
-  static KeyPathContextualMismatch *
-  create(ConstraintSystem &cs, Type lhs, Type rhs, ConstraintLocator *locator);
-
-  static bool classof(const ConstraintFix *fix) {
-    return fix->getKind() == FixKind::IgnoreKeyPathContextualMismatch;
-  }
-};
-
 /// Detect situations when argument of the @autoclosure parameter is itself
 /// marked as @autoclosure and is not applied. Form a fix which suggests a
 /// proper way to forward such arguments, e.g.:

lib/Sema/CSBindings.cpp

@@ -2060,8 +2060,15 @@ bool TypeVarBindingProducer::computeNext() {
 
       for (auto supertype : enumerateDirectSupertypes(type)) {
         // If we're not allowed to try this binding, skip it.
-        if (auto simplifiedSuper = checkTypeOfBinding(TypeVar, supertype))
-          addNewBinding(binding.withType(*simplifiedSuper));
+        if (auto simplifiedSuper = checkTypeOfBinding(TypeVar, supertype)) {
+          auto supertype = *simplifiedSuper;
+          // A key path type cannot be bound to type-erased key path variants.
+          if (TypeVar->getImpl().isKeyPathType() &&
+              (supertype->isPartialKeyPath() || supertype->isAnyKeyPath()))
+            continue;
+
+          addNewBinding(binding.withType(supertype));
+        }
       }
     }
   }

lib/Sema/CSDiagnostics.cpp

@@ -1493,10 +1493,10 @@ bool MemberAccessOnOptionalBaseFailure::diagnoseAsError() {
     } else {
       emitDiagnostic(diag::invalid_optional_inferred_keypath_root, baseType,
                      Member, unwrappedBaseType);
-      emitDiagnostic(diag::optional_key_path_root_base_chain, Member)
-          .fixItInsert(sourceRange.End, "?.");
-      emitDiagnostic(diag::optional_key_path_root_base_unwrap, Member)
-          .fixItInsert(sourceRange.End, "!.");
+      // Note that unwrapping fix-its cannot be suggested in this case
+      // because neither `.?` nor `.!` can be used to start a key path
+      // literal. Suggesting an explicit type here won't work either
+      // because contextual root is going to be optional still.
     }
   } else {
     // Check whether or not the base of this optional unwrap is implicit self

lib/Sema/CSFix.cpp

@@ -1296,13 +1296,6 @@ AllowInvalidRefInKeyPath::create(ConstraintSystem &cs, RefKind kind,
       AllowInvalidRefInKeyPath(cs, kind, member, locator);
 }
 
-KeyPathContextualMismatch *
-KeyPathContextualMismatch::create(ConstraintSystem &cs, Type lhs, Type rhs,
-                                  ConstraintLocator *locator) {
-  return new (cs.getAllocator())
-      KeyPathContextualMismatch(cs, lhs, rhs, locator);
-}
-
 bool RemoveAddressOf::diagnose(const Solution &solution, bool asNote) const {
   InvalidUseOfAddressOf failure(solution, getFromType(), getToType(),
                                 getLocator());

lib/Sema/CSSimplify.cpp

@@ -5958,14 +5958,6 @@ bool ConstraintSystem::repairFailures(
     if (repairViaBridgingCast(*this, lhs, rhs, conversionsOrFixes, locator))
       break;
 
-    // If both types are key path, the only differences
-    // between them are mutability and/or root, value type mismatch.
-    if (isKnownKeyPathType(lhs) && isKnownKeyPathType(rhs)) {
-      auto *fix = KeyPathContextualMismatch::create(
-          *this, lhs, rhs, getConstraintLocator(locator));
-      conversionsOrFixes.push_back(fix);
-    }
-
     if (lhs->is<FunctionType>() && !rhs->is<AnyFunctionType>() &&
         isExpr<ClosureExpr>(anchor)) {
       auto *fix = ContextualMismatch::create(*this, lhs, rhs,
@@ -6608,8 +6600,20 @@ bool ConstraintSystem::repairFailures(
     if (hasFixFor(lastCompLoc, FixKind::AllowTypeOrInstanceMember))
       return true;
 
+    auto *keyPathLoc = getConstraintLocator(anchor);
+
+    if (hasFixFor(keyPathLoc))
+      return true;
+
+    if (auto contextualInfo = getContextualTypeInfo(anchor)) {
+      if (hasFixFor(getConstraintLocator(
+              keyPathLoc,
+              LocatorPathElt::ContextualType(contextualInfo->purpose))))
+        return true;
+    }
+
     conversionsOrFixes.push_back(IgnoreContextualType::create(
-        *this, lhs, rhs, getConstraintLocator(anchor)));
+        *this, lhs, rhs, keyPathLoc));
     break;
   }
   default:
@@ -10841,6 +10845,12 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
       if (result.ViableCandidates.empty() && result.UnviableCandidates.empty())
         return fixMissingMember(origBaseTy, memberTy, locator);
 
+      bool baseIsKeyPathRootType = [&]() {
+        auto keyPathComponent =
+            locator->getLastElementAs<LocatorPathElt::KeyPathComponent>();
+        return keyPathComponent && keyPathComponent->getIndex() == 0;
+      }();
+
       // The result of the member access can either be the expected member type
       // (for '!' or optional members with '?'), or the original member type
       // with one extra level of optionality ('?' with non-optional members).
@@ -10854,13 +10864,17 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
           *this, ConstraintKind::Bind,
           UnwrapOptionalBase::create(*this, member, baseObjTy, locator),
           memberTy, innerTV, locator);
-      auto optionalResult = Constraint::createFixed(
-          *this, ConstraintKind::Bind,
-          UnwrapOptionalBase::createWithOptionalResult(*this, member,
-                                                       baseObjTy, locator),
-          optTy, memberTy, locator);
       optionalities.push_back(nonoptionalResult);
-      optionalities.push_back(optionalResult);
+
+      if (!baseIsKeyPathRootType) {
+        auto optionalResult = Constraint::createFixed(
+            *this, ConstraintKind::Bind,
+            UnwrapOptionalBase::createWithOptionalResult(*this, member,
+                                                         baseObjTy, locator),
+            optTy, memberTy, locator);
+        optionalities.push_back(optionalResult);
+      }
+
       addDisjunctionConstraint(optionalities, locator);
 
       // Look through one level of optional.
@@ -11636,6 +11650,13 @@ bool ConstraintSystem::resolveKeyPath(TypeVariableType *typeVar,
         contextualType = BoundGenericType::get(
             keyPathTy->getDecl(), keyPathTy->getParent(), {root, value});
       }
+    } else if (contextualType->isPlaceholder()) {
+      auto root = simplifyType(getKeyPathRootType(keyPath));
+      if (!(root->isTypeVariableOrMember() || root->isPlaceholder())) {
+        auto value = getKeyPathValueType(keyPath);
+        contextualType =
+            BoundGenericType::get(ctx.getKeyPathDecl(), Type(), {root, value});
+      }
     }
   }
 
@@ -12150,12 +12171,14 @@ ConstraintSystem::simplifyKeyPathConstraint(
     }
 
     if (boundRoot &&
-        matchTypes(boundRoot, rootTy, ConstraintKind::Bind, subflags, locator)
+        matchTypes(rootTy, boundRoot, ConstraintKind::Bind, subflags,
+                   locator.withPathElement(ConstraintLocator::KeyPathRoot))
             .isFailure())
       return false;
 
     if (boundValue &&
-        matchTypes(boundValue, valueTy, ConstraintKind::Bind, subflags, locator)
+        matchTypes(valueTy, boundValue, ConstraintKind::Bind, subflags,
+                   locator.withPathElement(ConstraintLocator::KeyPathValue))
             .isFailure())
       return false;
 
@@ -12206,6 +12229,16 @@ ConstraintSystem::simplifyKeyPathConstraint(
                  tv->getImpl().canBindToHole();
         })) {
       (void)tryMatchRootAndValueFromType(keyPathTy);
+
+      // If the type of the key path is not yet resolved simplifying this
+      // constraint would disconnect it from root and value, let's bind it
+      // to a placeholder type to make sure this doesn't happen.
+      if (auto *typeVar = keyPathTy->getAs<TypeVariableType>()) {
+        return matchTypes(keyPathTy, PlaceholderType::get(Context, typeVar),
+                          ConstraintKind::Bind, subflags,
+                          locator.getBaseLocator());
+      }
+
       return SolutionKind::Solved;
     }
   }
@@ -12364,21 +12397,58 @@ ConstraintSystem::simplifyKeyPathConstraint(
       kpDecl = getASTContext().getWritableKeyPathDecl();
   }
 
+  auto formUnsolved = [&]() {
+    addUnsolvedConstraint(Constraint::create(
+        *this, ConstraintKind::KeyPath, keyPathTy, rootTy, valueTy,
+        locator.getBaseLocator(), componentTypeVars));
+  };
+
   auto loc = locator.getBaseLocator();
   if (definitelyFunctionType) {
     increaseScore(SK_FunctionConversion, locator);
     return SolutionKind::Solved;
   } else if (!anyComponentsUnresolved ||
              (definitelyKeyPathType && capability == ReadOnly)) {
-    auto resolvedKPTy =
-      BoundGenericType::get(kpDecl, nullptr, {rootTy, valueTy});
-    return matchTypes(resolvedKPTy, keyPathTy, ConstraintKind::Bind, subflags,
-                      loc);
+    // If key path is connected to a disjunction (i.e. through coercion
+    // or used as an argument to a function/subscipt call) it cannot be
+    // bound until the choice is selected because it's undetermined
+    // until then whether key path is implicitly converted to a function
+    // type or not.
+    //
+    // \code
+    // struct Data {
+    //   var value: Int = 42
+    // }
+    //
+    // func test<S: Sequence>(_: S, _: (S.Element) -> Int) {}
+    // func test<C: Collection>(_: C, _: (C.Element) -> Int) {}
+    //
+    // func test(arr: [Data]) {
+    //  test(arr, \Data.value)
+    // }
+    // \endcode
+    //
+    // In this example if we did allow to bind the key path before
+    // an overload of `test` is selected, we'd end up with no solutions
+    // because the type of the key path expression is actually: '(Data) -> Int'
+    // and not 'WritableKeyPath<Data, Int>`.
+    auto *typeVar = keyPathTy->getAs<TypeVariableType>();
+    if (typeVar && findConstraintThroughOptionals(
+                       typeVar, OptionalWrappingDirection::Unwrap,
+                       [&](Constraint *match, TypeVariableType *) {
+                         return match->getKind() ==
+                                    ConstraintKind::ApplicableFunction ||
+                                match->getKind() == ConstraintKind::Disjunction;
+                       })) {
+      formUnsolved();
+    } else {
+      auto resolvedKPTy =
+          BoundGenericType::get(kpDecl, nullptr, {rootTy, valueTy});
+      return matchTypes(resolvedKPTy, keyPathTy, ConstraintKind::Bind,
+                        subflags, loc);
+    }
   } else {
-    addUnsolvedConstraint(Constraint::create(*this, ConstraintKind::KeyPath,
-                                             keyPathTy, rootTy, valueTy,
-                                             locator.getBaseLocator(),
-                                             componentTypeVars));
+    formUnsolved();
   }
   return SolutionKind::Solved;
 }
@@ -14987,7 +15057,6 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::RemoveExtraneousArguments:
   case FixKind::SpecifyTypeForPlaceholder:
   case FixKind::AllowAutoClosurePointerConversion:
-  case FixKind::IgnoreKeyPathContextualMismatch:
   case FixKind::NotCompileTimeConst:
   case FixKind::RenameConflictingPatternVariables:
   case FixKind::MustBeCopyable:

test/Constraints/keypath.swift

@@ -255,9 +255,11 @@ func rdar32101765() {
   }
 
   let _: KeyPath<R32101765, Float> = \.prop32101765
-  // expected-error@-1 {{key path value type 'Int' cannot be converted to contextual type 'Float'}}
+  // expected-error@-1 {{cannot assign value of type 'KeyPath<R32101765, Int>' to type 'KeyPath<R32101765, Float>'}}
+  // expected-note@-2 {{arguments to generic parameter 'Value' ('Int' and 'Float') are expected to be equal}}
   let _: KeyPath<R32101765, Float> = \R32101765.prop32101765
-  // expected-error@-1 {{key path value type 'Int' cannot be converted to contextual type 'Float'}}
+  // expected-error@-1 {{cannot assign value of type 'KeyPath<R32101765, Int>' to type 'KeyPath<R32101765, Float>'}}
+  // expected-note@-2 {{arguments to generic parameter 'Value' ('Int' and 'Float') are expected to be equal}}
   let _: KeyPath<R32101765, Float> = \.prop32101765.unknown
   // expected-error@-1 {{type 'Int' has no member 'unknown'}}
   let _: KeyPath<R32101765, Float> = \R32101765.prop32101765.unknown

test/expr/unary/keypath/keypath.swift

@@ -794,9 +794,11 @@ func test_keypath_with_method_refs() {
   }
 
   let _: KeyPath<S, Int> = \.foo // expected-error {{key path cannot refer to instance method 'foo()'}}
-  // expected-error@-1 {{key path value type '() -> Int' cannot be converted to contextual type 'Int'}}
+  // expected-error@-1 {{cannot assign value of type 'KeyPath<S, () -> Int>' to type 'KeyPath<S, Int>'}}
+  // expected-note@-2 {{arguments to generic parameter 'Value' ('() -> Int' and 'Int') are expected to be equal}}
   let _: KeyPath<S, Int> = \.bar // expected-error {{key path cannot refer to static method 'bar()'}}
-  // expected-error@-1 {{key path value type '() -> Int' cannot be converted to contextual type 'Int'}}
+  // expected-error@-1 {{cannot assign value of type 'KeyPath<S, () -> Int>' to type 'KeyPath<S, Int>'}}
+  // expected-note@-2 {{arguments to generic parameter 'Value' ('() -> Int' and 'Int') are expected to be equal}}
   let _ = \S.Type.bar // expected-error {{key path cannot refer to static method 'bar()'}}
 
   struct A {
@@ -1008,16 +1010,10 @@ func testMemberAccessOnOptionalKeyPathComponent() {
   func kp(_: KeyPath<String?, Int>) {}
 
   kp(\.count) // expected-error {{key path root inferred as optional type 'String?' must be unwrapped to refer to member 'count' of unwrapped type 'String'}}
-  // expected-note@-1 {{chain the optional using '?.' to access unwrapped type member 'count'}} {{8-8=?.}}
-  // expected-note@-2 {{unwrap the optional using '!.' to access unwrapped type member 'count'}} {{8-8=!.}}
   let _ : KeyPath<String?, Int> = \.count // expected-error {{key path root inferred as optional type 'String?' must be unwrapped to refer to member 'count' of unwrapped type 'String'}}
-  // expected-note@-1 {{chain the optional using '?.' to access unwrapped type member 'count'}} {{37-37=?.}}
-  // expected-note@-2 {{unwrap the optional using '!.' to access unwrapped type member 'count'}} {{37-37=!.}}
 
   let _ : KeyPath<String?, Int> = \.utf8.count 
   // expected-error@-1 {{key path root inferred as optional type 'String?' must be unwrapped to refer to member 'utf8' of unwrapped type 'String'}}
-  // expected-note@-2 {{chain the optional using '?.' to access unwrapped type member 'utf8'}} {{37-37=?.}}
-  // expected-note@-3 {{unwrap the optional using '!.' to access unwrapped type member 'utf8'}} {{37-37=!.}}
 }
 
 func testSyntaxErrors() {
@@ -1067,8 +1063,9 @@ func f_56996() {
 // https://github.com/apple/swift/issues/55805
 // Key-path missing optional crashes compiler: Inactive constraints left over?
 func f_55805() {
-  let _: KeyPath<String?, Int?> = \.utf8.count // expected-error {{value of optional type 'String.UTF8View?' must be unwrapped to refer to member 'count' of wrapped base type 'String.UTF8View'}}
-  // expected-note@-1 {{chain the optional using '?' to access member 'count' only for non-'nil' base values}}
+  let _: KeyPath<String?, Int?> = \.utf8.count
+  // expected-error@-1 {{key path root inferred as optional type 'String?' must be unwrapped to refer to member 'utf8' of unwrapped type 'String'}}
+  // expected-error@-2 {{key path value type 'Int' cannot be converted to contextual type 'Int?'}}
 }
 
 // rdar://74711236 - crash due to incorrect member access in key path
@@ -1202,3 +1199,28 @@ func test_keypath_inference_from_existentials() {
   test(\.other, 42)  // Ok
   test(\.member, "") // Ok
 }
+
+// rdar://116376651 - key path type is bound before context is fully resolved.
+func keypath_to_func_conversion_as_arg_to_overloaded_func() {
+  struct Data {
+    var value: Int = 42
+  }
+
+  func test<S: Sequence>(_: S, _: (S.Element) -> Int) {}
+  func test<C: Collection>(_: C, _: (C.Element) -> Int) {}
+
+  func test(arr: [Data]) {
+    test(arr, \Data.value) // Ok
+  }
+}
+
+// https://github.com/apple/swift/issues/55436
+func test_keypath_coercion_to_function() {
+  struct User {
+    let email: String
+  }
+
+  let users = [User]()
+  let fn = \User.email as (User) -> String // Ok
+  _ = users.map(fn) // Ok
+}

test/expr/unary/keypath/salvage-with-other-type-errors.swift

@@ -6,7 +6,7 @@
 struct P<T: K> { }
 
 struct S {
-    init<B>(_ a: P<B>) { // expected-note {{in call to initializer}}
+    init<B>(_ a: P<B>) { // expected-note {{where 'B' = 'String'}}
         fatalError()
     }
 }
@@ -27,9 +27,8 @@ struct A {
 }
 
 extension A: K {
-  static let j = S(\A.id + "id") // expected-error {{generic parameter 'B' could not be inferred}}
-  // expected-error@-1 {{binary operator '+' cannot be applied to operands of type 'KeyPath<A, String>' and 'String'}}
-  // expected-note@-2 {{overloads for '+' exist with these partially matching parameter lists: (String, String)}}
+  static let j = S(\A.id + "id")
+  // expected-error@-1 {{initializer 'init(_:)' requires that 'String' conform to 'K'}}
 }
 
 // https://github.com/apple/swift/issues/47610