[BuilderTransform] Lift all restrictions from variable decls when AST transform is enabled

Result builders would be able to declare:
  - uninitialized variables
  - variables with property wrappers (with and without explicit initializer)
  - default initializable variables i.e. `var x: Int?`
  - computed variables
  - `lazy` variables

Author: xedin

lib/Sema/BuilderTransform.cpp

@@ -1015,22 +1015,14 @@ class ResultBuilderTransform
 
       if (auto *decl = element.dyn_cast<Decl *>()) {
         switch (decl->getKind()) {
-        case DeclKind::PatternBinding: {
-          if (!isValidPatternBinding(cast<PatternBindingDecl>(decl)))
-            return failTransform(decl);
-
-          LLVM_FALLTHROUGH;
-        }
-
         // Just ignore #if; the chosen children should appear in
         // the surrounding context.  This isn't good for source
         // tools but it at least works.
         case DeclKind::IfConfig:
         // Skip #warning/#error; we'll handle them when applying
         // the builder.
         case DeclKind::PoundDiagnostic:
-        // Ignore variable declarations, because they're always
-        // handled within their enclosing pattern bindings.
+        case DeclKind::PatternBinding:
         case DeclKind::Var:
         case DeclKind::Param:
           newBody.push_back(element);
@@ -1567,30 +1559,6 @@ class ResultBuilderTransform
     return DoStmt::createImplicit(ctx, LabeledStmtInfo(), doBody);
   }
 
-  bool isValidPatternBinding(PatternBindingDecl *PB) {
-    // Enforce some restrictions on local variables inside a result builder.
-    for (unsigned i : range(PB->getNumPatternEntries())) {
-      // The pattern binding must have an initial value expression.
-      if (!PB->isExplicitlyInitialized(i))
-        return false;
-
-      // Each variable bound by the pattern must be stored, and cannot
-      // have observers.
-      SmallVector<VarDecl *, 8> variables;
-      PB->getPattern(i)->collectVariables(variables);
-
-      for (auto *var : variables) {
-        if (!var->getImplInfo().isSimpleStored())
-          return false;
-
-        // Also check for invalid attributes.
-        TypeChecker::checkDeclAttributes(var);
-      }
-    }
-
-    return true;
-  }
-
   UNSUPPORTED_STMT(Throw)
   UNSUPPORTED_STMT(Return)
   UNSUPPORTED_STMT(Yield)

test/Constraints/result_builder_ast_transform.swift

@@ -0,0 +1,165 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -enable-experimental-feature ResultBuilderASTTransform -module-name main -I %t -L %t %s -o %t/main %target-rpath(%t)
+// RUN: %target-codesign %t/main
+// RUN: %target-run %t/main | %FileCheck %s
+
+// REQUIRES: executable_test
+
+@propertyWrapper
+struct Wrapper<Value> {
+  public var value: Value
+
+  init(wrappedValue: Value) {
+    self.value = wrappedValue
+  }
+
+  var projectedValue: Self { return self }
+
+  var wrappedValue: Value {
+    get { self.value }
+    set { self.value = newValue }
+  }
+
+  func test() -> Int { 42 }
+}
+
+extension Wrapper where Value: ExpressibleByNilLiteral {
+  init() {
+    self.value = nil
+  }
+}
+
+enum Either<T,U> {
+  case first(T)
+  case second(U)
+}
+
+@resultBuilder
+struct TupleBuilder {
+  static func buildBlock() -> () { }
+
+  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 buildDo<T>(_ value: T) -> T { return value }
+  static func buildOptional<T>(_ value: T?) -> T? { return value }
+
+  static func buildEither<T,U>(first value: T) -> Either<T,U> {
+    return .first(value)
+  }
+  static func buildEither<T,U>(second value: U) -> Either<T,U> {
+    return .second(value)
+  }
+}
+
+func tuplify<T>(_ cond: Bool, @TupleBuilder body: (Bool) -> T) {
+  print(body(cond))
+}
+
+tuplify(true) { cond in
+  @Wrapper var x: Int?
+  x
+  x = 42
+  x
+}
+// CHECK: (nil, (), Optional(42))
+
+tuplify(true) { cond in
+  @Wrapper var x: Int = 42
+  x
+  if cond {
+    $x
+  }
+}
+// CHECK: (42, Optional(main.Wrapper<Swift.Int>(value: 42)))
+
+tuplify(true) { cond in
+  @Wrapper(wrappedValue: 42) var x: Int
+
+  if cond && x == 42 {
+    x = 30
+    $x
+  }
+
+  x
+}
+// CHECK: (Optional(((), main.Wrapper<Swift.Int>(value: 30))), 30)
+
+tuplify(true) { cond in
+  if cond {
+    @Wrapper(wrappedValue: 42) var x: Int
+    if $x.test() > 0 {
+      x
+    }
+  }
+
+  ""
+}
+// CHECK: (Optional(Optional(42)), "")
+
+tuplify(true) { cond in
+  var x: Int?
+
+  if cond {
+    var y: Int?
+    x = 1
+    y = x
+    y
+  } else {
+    x = 0
+  }
+
+  x
+}
+// CHECK: (main.Either<((), (), Swift.Optional<Swift.Int>), ()>.first((), (), Optional(1)), Optional(1))
+
+tuplify(true) { cond in
+  ""
+
+  var x: Int {
+    get { 42 }
+  }
+
+  if cond {
+    x
+  }
+
+  ""
+}
+// CHECK: ("", Optional(42), "")
+
+tuplify(true) { cond in
+  lazy var x: Int = {
+    42
+  }()
+
+  if cond {
+    x
+    x = 0
+    x
+  }
+
+  ""
+}
+// CHECK: (Optional((42, (), 0)), "")