[Sema] Fix issue 65330 Unhelpful error when missing contextually requ…

lib/Sema/CSDiagnostics.cpp

@@ -2577,7 +2577,6 @@ bool ContextualFailure::diagnoseAsError() {
     }
     return false;
   }
-
   case ConstraintLocator::UnresolvedMemberChainResult: {
     auto &solution = getSolution();
 
@@ -3528,6 +3527,66 @@ ContextualFailure::getDiagnosticFor(ContextualTypePurpose context,
   return None;
 }
 
+bool NonClassTypeToAnyObjectConversionFailure::diagnoseAsError() {
+  auto locator = getLocator();
+  if (locator->isForContextualType()) {
+    return ContextualFailure::diagnoseAsError();
+  }
+
+  auto fromType = getFromType();
+  auto toType = getToType();
+  assert(fromType);
+  assert(toType);
+  if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
+    ArgumentMismatchFailure failure(getSolution(), fromType, toType, locator);
+    return failure.diagnoseAsError();
+  }
+
+  Optional<Diag<Type, Type>> diagnostic;
+
+  bool forProtocol = toType->isConstraintType();
+  auto rawAnchor = getRawAnchor();
+
+  if (isExpr<ArrayExpr>(rawAnchor)) {
+    diagnostic = forProtocol ? diag::cannot_convert_array_element_protocol
+                             : diag::cannot_convert_array_element;
+  } else if (isExpr<DictionaryExpr>(rawAnchor)) {
+    auto lastElem = locator->getLastElementAs<LocatorPathElt::TupleElement>();
+    if (lastElem && lastElem->getIndex() == 0) {
+      diagnostic = forProtocol ? diag::cannot_convert_dict_key_protocol
+                               : diag::cannot_convert_dict_key;
+    } else {
+      diagnostic = forProtocol ? diag::cannot_convert_dict_value_protocol
+                               : diag::cannot_convert_dict_value;
+    }
+  } else if (toType->isAnyObject()) {
+    diagnostic = diag::cannot_convert_initializer_value_anyobject;
+  }
+
+  if (diagnostic.hasValue()) {
+    emitDiagnostic(*diagnostic, fromType, toType);
+    return true;
+  }
+
+  return false;
+}
+
+bool NonClassTypeToAnyObjectConversionFailure::diagnoseAsNote() {
+  auto *locator = getLocator();
+
+  if (locator->isForContextualType()) {
+    return ContextualFailure::diagnoseAsNote();
+  }
+
+  if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
+    ArgumentMismatchFailure failure(getSolution(), getFromType(), getToType(),
+                                    getLocator());
+    return failure.diagnoseAsNote();
+  }
+
+  return false;
+}
+
 bool TupleContextualFailure::diagnoseAsError() {
   Diag<Type, Type> diagnostic;
   auto purpose = getContextualTypePurpose();

lib/Sema/CSDiagnostics.h

@@ -804,6 +804,19 @@ class ContextualFailure : public FailureDiagnostic {
   }
 };
 
+class NonClassTypeToAnyObjectConversionFailure final
+    : public ContextualFailure {
+
+public:
+  NonClassTypeToAnyObjectConversionFailure(const Solution &solution, Type lhs,
+                                           Type rhs, ConstraintLocator *locator)
+      : ContextualFailure(solution, lhs, rhs, locator, FixBehavior::Error) {}
+
+  bool diagnoseAsError() override;
+
+  bool diagnoseAsNote() override;
+};
+
 /// Diagnose errors related to using an array literal where a
 /// dictionary is expected.
 class ArrayLiteralToDictionaryConversionFailure final : public ContextualFailure {

lib/Sema/CSFix.cpp

@@ -1934,18 +1934,10 @@ bool AllowNonClassTypeToConvertToAnyObject::diagnose(const Solution &solution,
                                                      bool asNote) const {
   auto *locator = getLocator();
 
-  if (locator->isForContextualType()) {
-    ContextualFailure failure(solution, getFromType(), getToType(), locator);
-    return failure.diagnose(asNote);
-  }
+  NonClassTypeToAnyObjectConversionFailure failure(solution, getFromType(),
+                                                   getToType(), locator);
 
-  if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
-    ArgumentMismatchFailure failure(solution, getFromType(), getToType(),
-                                    locator);
-    return failure.diagnose(asNote);
-  }
-
-  return false;
+  return failure.diagnose(asNote);
 }
 
 AllowNonClassTypeToConvertToAnyObject *

test/Sema/contextual-conversion-error-for-structural-position.swift

@@ -0,0 +1,9 @@
+// RUN: %target-typecheck-verify-swift
+
+let _: AnyObject = "a" // expected-error {{value of type 'String' expected to be instance of class or class-constrained type}}
+
+let _: [AnyObject] = ["a"] // expected-error {{cannot convert value of type 'String' to expected element type 'AnyObject'}}
+let _: [String: AnyObject] = ["a": "a"] // expected-error {{cannot convert value of type 'String' to expected dictionary value type 'AnyObject'}}
+let _: [AnyObject: String] = ["a": "a"] // expected-error {{type 'AnyObject' does not conform to protocol 'Hashable'}}
+// expected-error@-1 {{cannot convert value of type 'String' to expected dictionary key type 'AnyObject'}}
+let _: (AnyObject, Void) = ("a", ()) // expected-error {{value of type 'String' expected to be instance of class or class-constrained type}}

test/Sema/generic-subscript.swift

@@ -1,16 +1,13 @@
 // RUN: %target-typecheck-verify-swift
 
 protocol P {
-  subscript<Value>(x: Value) -> Int  // expected-note {{protocol requires subscript with type '<Value> (Value) -> Int'; do you want to add a stub?}}
-  {
+  subscript<Value>(x: Value) -> Int { // expected-note {{protocol requires subscript with type '<Value> (Value) -> Int'; do you want to add a stub?}}
     get
   }
 }
 
-struct S: P  // expected-error {{type 'S' does not conform to protocol 'P'}}
-{
-  subscript<Value>(x: Int) -> Value  // expected-note {{candidate has non-matching type '<Value> (Int) -> Value'}}
-  {
+struct S : P { // expected-error {{type 'S' does not conform to protocol 'P'}}
+  subscript<Value>(x: Int) -> Value { // expected-note {{candidate has non-matching type '<Value> (Int) -> Value'}}
   }  // expected-error {{missing return in subscript expected to return 'Value'}}
 }
 
@@ -21,8 +18,7 @@ struct S2: P {
 }
 
 protocol P2 {
-  subscript(x: Int) -> Int
-  {
+  subscript(x: Int) -> Int {
     get
   }
 }