[sending] Fix parsing of sending results in closures.

The specific problem is that in the type checker where we validate that it is
legal to apply sending to a result, we attempt to use the TypeResolutionFlags...
but only given the previous implementation would get access to
TypeResolutionFlags::InContext.

To fix this I renamed the current TypeResolutionFlags::ClosureExpr ->
ClosureExprParameters and added a new flag
TypeResolutionFlags::ClosureExprResult. By not reusing ClosureExprParameters, I
am being more conservative to ensure my work here does not break parameters as
well.

Author: gottesmm

lib/Sema/CSGen.cpp

@@ -2543,7 +2543,7 @@ namespace {
 
           const auto resolvedTy = resolveTypeReferenceInExpression(
               closure->getExplicitResultTypeRepr(),
-              TypeResolverContext::InExpression, resultLocator);
+              TypeResolverContext::ClosureExprResult, resultLocator);
           if (resolvedTy)
             return resolvedTy;
         }

lib/Sema/TypeCheckDecl.cpp

@@ -2297,7 +2297,7 @@ static Type validateParameterType(ParamDecl *decl) {
   TypeResolutionOptions options(std::nullopt);
   OpenUnboundGenericTypeFn unboundTyOpener = nullptr;
   if (isa<AbstractClosureExpr>(dc)) {
-    options = TypeResolutionOptions(TypeResolverContext::ClosureExpr);
+    options = TypeResolutionOptions(TypeResolverContext::ClosureExprParameters);
     options |= TypeResolutionFlags::AllowUnspecifiedTypes;
     unboundTyOpener = [](auto unboundTy) {
       // FIXME: Don't let unbound generic types escape type resolution.

lib/Sema/TypeCheckType.cpp

@@ -159,7 +159,8 @@ static unsigned getGenericRequirementKind(TypeResolutionOptions options) {
   case TypeResolverContext::ForEachStmt:
   case TypeResolverContext::PatternBindingDecl:
   case TypeResolverContext::EditorPlaceholderExpr:
-  case TypeResolverContext::ClosureExpr:
+  case TypeResolverContext::ClosureExprParameters:
+  case TypeResolverContext::ClosureExprResult:
   case TypeResolverContext::VariadicFunctionInput:
   case TypeResolverContext::InoutFunctionInput:
   case TypeResolverContext::FunctionResult:
@@ -4971,7 +4972,8 @@ TypeResolver::resolveSendingTypeRepr(SendingTypeRepr *repr,
     return ErrorType::get(getASTContext());
   }
 
-  if (!options.is(TypeResolverContext::FunctionResult) &&
+  if (!options.is(TypeResolverContext::ClosureExprResult) &&
+      !options.is(TypeResolverContext::FunctionResult) &&
       (!options.is(TypeResolverContext::FunctionInput) ||
        options.hasBase(TypeResolverContext::EnumElementDecl))) {
     diagnoseInvalid(repr, repr->getSpecifierLoc(),
@@ -5193,7 +5195,8 @@ NeverNullType TypeResolver::resolveImplicitlyUnwrappedOptionalType(
   case TypeResolverContext::InExpression:
   case TypeResolverContext::EditorPlaceholderExpr:
   case TypeResolverContext::AbstractFunctionDecl:
-  case TypeResolverContext::ClosureExpr:
+  case TypeResolverContext::ClosureExprParameters:
+  case TypeResolverContext::ClosureExprResult:
   case TypeResolverContext::Inherited:
   case TypeResolverContext::GenericParameterInherited:
   case TypeResolverContext::AssociatedTypeInherited:

lib/Sema/TypeCheckType.h

@@ -119,7 +119,10 @@ enum class TypeResolverContext : uint8_t {
   SubscriptDecl,
 
   /// Whether we are checking the parameter list of a closure.
-  ClosureExpr,
+  ClosureExprParameters,
+
+  /// Whether we are checking the result of a closure.
+  ClosureExprResult,
 
   /// Whether we are in the input type of a function, or under one level of
   /// tuple type.  This is not set for multi-level tuple arguments.
@@ -272,7 +275,8 @@ class TypeResolutionOptions {
     case Context::ForEachStmt:
     case Context::PatternBindingDecl:
     case Context::EditorPlaceholderExpr:
-    case Context::ClosureExpr:
+    case Context::ClosureExprParameters:
+    case Context::ClosureExprResult:
       return true;
     case Context::None:
     case Context::ScalarGenericArgument:
@@ -332,7 +336,8 @@ class TypeResolutionOptions {
     case Context::ForEachStmt:
     case Context::PatternBindingDecl:
     case Context::EditorPlaceholderExpr:
-    case Context::ClosureExpr:
+    case Context::ClosureExprParameters:
+    case Context::ClosureExprResult:
     case Context::FunctionInput:
     case Context::VariadicFunctionInput:
     case Context::InoutFunctionInput:
@@ -376,7 +381,8 @@ class TypeResolutionOptions {
     case Context::ExplicitCastExpr:
     case Context::ForEachStmt:
     case Context::EditorPlaceholderExpr:
-    case Context::ClosureExpr:
+    case Context::ClosureExprParameters:
+    case Context::ClosureExprResult:
     case Context::InoutFunctionInput:
     case Context::FunctionResult:
     case Context::SubscriptDecl:
@@ -419,7 +425,8 @@ class TypeResolutionOptions {
     case Context::ForEachStmt:
     case Context::PatternBindingDecl:
     case Context::EditorPlaceholderExpr:
-    case Context::ClosureExpr:
+    case Context::ClosureExprParameters:
+    case Context::ClosureExprResult:
     case Context::VariadicFunctionInput:
     case Context::InoutFunctionInput:
     case Context::FunctionResult:

test/Concurrency/sending_closure_inference.swift

@@ -42,3 +42,7 @@ func testNamedTypeParameterSendingInference() {
 func testSendingResultInference() {
   let _: () -> sending String = { "" }
 }
+
+func testSendingResultOnClosure() {
+  let _ = { (x: String) -> sending String in x }
+}