[Function builders] Add support for function builders on stored struct properties

lib/SILGen/SILGenConstructor.cpp

@@ -18,6 +18,7 @@
 #include "SILGenFunctionBuilder.h"
 #include "Scope.h"
 #include "swift/AST/ASTMangler.h"
+#include "swift/AST/ForeignErrorConvention.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/ParameterList.h"
 #include "swift/AST/PropertyWrappers.h"
@@ -211,8 +212,24 @@ static void emitImplicitValueConstructor(SILGenFunction &SGF,
                "number of args does not match number of fields");
         (void)eltEnd;
         FullExpr scope(SGF.Cleanups, field->getParentPatternBinding());
+
+        RValue arg = std::move(*elti);
+
+        // If the stored property has an attached function builder and its
+        // type is not a function type, the argument is a noescape closure
+        // that needs to be called.
+        if (field->getFunctionBuilderType()) {
+          if (!field->getValueInterfaceType()
+                  ->lookThroughAllOptionalTypes()->is<AnyFunctionType>()) {
+            auto resultTy = cast<FunctionType>(arg.getType()).getResult();
+            arg = SGF.emitMonomorphicApply(
+                Loc, std::move(arg).getAsSingleValue(SGF, Loc), { }, resultTy,
+                resultTy, ApplyOptions::None, None, None);
+          }
+        }
+
         maybeEmitPropertyWrapperInitFromValue(SGF, Loc, field, subs,
-                                              std::move(*elti))
+                                              std::move(arg))
           .forwardInto(SGF, Loc, init.get());
         ++elti;
       } else {

lib/Sema/CodeSynthesis.cpp

@@ -261,6 +261,20 @@ static ConstructorDecl *createImplicitConstructor(NominalTypeDecl *decl,
         }
       }
 
+      Type functionBuilderType= var->getFunctionBuilderType();
+      if (functionBuilderType) {
+        // If the variable's type is structurally a function type, use that
+        // type. Otherwise, form a non-escaping function type for the function
+        // parameter.
+        bool isStructuralFunctionType =
+            varInterfaceType->lookThroughAllOptionalTypes()
+              ->is<AnyFunctionType>();
+        if (!isStructuralFunctionType) {
+          auto extInfo = ASTExtInfoBuilder().withNoEscape().build();
+          varInterfaceType = FunctionType::get({ }, varInterfaceType, extInfo);
+        }
+      }
+
       // Create the parameter.
       auto *arg = new (ctx)
           ParamDecl(SourceLoc(), Loc,
@@ -273,6 +287,14 @@ static ConstructorDecl *createImplicitConstructor(NominalTypeDecl *decl,
       // Don't allow the parameter to accept temporary pointer conversions.
       arg->setNonEphemeralIfPossible();
 
+      // Attach a function builder attribute if needed.
+      if (functionBuilderType) {
+        auto typeExpr = TypeExpr::createImplicit(functionBuilderType, ctx);
+        auto attr = CustomAttr::create(
+            ctx, SourceLoc(), typeExpr, /*implicit=*/true);
+        arg->getAttrs().add(attr);
+      }
+
       maybeAddMemberwiseDefaultArg(arg, var, params.size(), ctx);
 
       params.push_back(arg);

lib/Sema/TypeCheckAttr.cpp

@@ -2987,8 +2987,19 @@ void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
     } else if (auto storage = dyn_cast<AbstractStorageDecl>(D)) {
       decl = storage;
 
-      // Check whether this is a property without an explicit getter.
+      // Check whether this is a storage declaration that is not permitted
+      // to have a function builder attached.
       auto shouldDiagnose = [&]() -> bool {
+        // An uninitialized stored property in a struct can have a function
+        // builder attached.
+        if (auto var = dyn_cast<VarDecl>(decl)) {
+          if (var->isInstanceMember() &&
+              isa<StructDecl>(var->getDeclContext()) &&
+              !var->getParentInitializer()) {
+            return false;
+          }
+        }
+
         auto getter = storage->getParsedAccessor(AccessorKind::Get);
         if (!getter)
           return true;

test/Constraints/function_builder.swift

@@ -767,3 +767,24 @@ do {
 } catch {
   fatalError("Threw something else?")
 }
+
+// CHECK: testStoredProperties
+struct MyTupleStruct<T, U> {
+  @TupleBuilder let first: () -> T
+  @TupleBuilder let second: U
+}
+
+print("testStoredProperties")
+let ts1 = MyTupleStruct {
+  1
+  "hello"
+  if true {
+    "conditional"
+  }
+} second: {
+  3.14159
+  "blah"
+}
+
+// CHECK: MyTupleStruct<(Int, String, Optional<String>), (Double, String)>(first: (Function), second: (3.14159, "blah"))
+print(ts1)

test/SILGen/function_builder_memberwise.swift

@@ -0,0 +1,57 @@
+// RUN: %target-swift-emit-silgen %s | %FileCheck %s
+
+@_functionBuilder
+struct TupleBuilder {
+  static func buildBlock<T1>(_ t1: T1) -> (T1) {
+    return (t1)
+  }
+
+  static func buildBlock<T1, T2>(_ t1: T1, _ t2: T2) -> (T1, T2) {
+    return (t1, t2)
+  }
+
+  static func buildBlock<T1, T2, T3>(_ t1: T1, _ t2: T2, _ t3: T3)
+      -> (T1, T2, T3) {
+    return (t1, t2, t3)
+  }
+
+  static func buildBlock<T1, T2, T3, T4>(_ t1: T1, _ t2: T2, _ t3: T3, _ t4: T4)
+      -> (T1, T2, T3, T4) {
+    return (t1, t2, t3, t4)
+  }
+
+  static func buildBlock<T1, T2, T3, T4, T5>(
+    _ t1: T1, _ t2: T2, _ t3: T3, _ t4: T4, _ t5: T5
+  ) -> (T1, T2, T3, T4, T5) {
+    return (t1, t2, t3, t4, t5)
+  }
+
+  static func buildOptional<T>(_ value: T?) -> T? { return value }
+}
+
+struct MyTupleStruct<T, U> {
+  @TupleBuilder let first: () -> T
+  @TupleBuilder let second: U
+  // CHECK: init(@TupleBuilder first: @escaping () -> T, @TupleBuilder second: () -> U)
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s27function_builder_memberwise13MyTupleStructV5first6secondACyxq_Gxyc_q_yXEtcfC : $@convention(method) <T, U> (@owned @callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <T>, @noescape @callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <U>, @thin MyTupleStruct<T, U>.Type) -> @out MyTupleStruct<T, U> {
+// CHECK: bb0([[SELF:%.*]] : $*MyTupleStruct<T, U>, [[FIRST:%.*]] : @owned $@callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <T>, [[SECOND:%.*]] : $@noescape @callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <U>, [[META:%.*]] : $@thin MyTupleStruct<T, U>.Type):
+// CHECK-NEXT:   [[FIRST_ADDR:%.*]] = struct_element_addr [[SELF]] : $*MyTupleStruct<T, U>, #MyTupleStruct.first
+// CHECK-NEXT:   store [[FIRST]] to [init] [[FIRST_ADDR]] : $*@callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <T> 
+// CHECK-NEXT:   [[SECOND_ADDR:%.*]] = struct_element_addr [[SELF]] : $*MyTupleStruct<T, U>, #MyTupleStruct.second
+// CHECK-NEXT:   [[CALL_RESULT:%.*]] = alloc_stack $U
+// CHECK-NEXT:   apply [[SECOND]]([[CALL_RESULT]]) : $@noescape @callee_guaranteed @substituted <τ_0_0> () -> @out τ_0_0 for <U>
+// CHECK-NEXT:   copy_addr [take] [[CALL_RESULT]] to [initialization] [[SECOND_ADDR]] : $*U
+func trigger(cond: Bool) {
+  _ = MyTupleStruct {
+    1
+    "hello"
+    if cond {
+      "conditional"
+    }
+  } second: {
+    3.14159
+    "blah"
+  }
+}