[Sema] Prevent the initializer being double check by its backing storage.

Author: hank121314

include/swift/AST/Decl.h

@@ -1589,6 +1589,9 @@ class PatternBindingEntry {
   /// Values captured by this initializer.
   CaptureInfo Captures;
 
+  /// Whether the initializer is synthesized by type check.
+  bool IsSynthesized = false;
+
   friend class Parser;
   friend class PatternBindingInitializer;
   friend class PatternBindingDecl;
@@ -1702,6 +1705,9 @@ class PatternBindingEntry {
     PatternAndFlags.setInt(PatternAndFlags.getInt() | Flags::Subsumed);
   }
 
+  bool isInitializerSynthesized() const { return IsSynthesized; }
+  void setInitializerSynthesized(bool value = true) { IsSynthesized = value; }
+
   /// Returns \c true if the debugger created this pattern binding entry.
   bool isFromDebugger() const {
     return InitContextAndFlags.getInt().contains(PatternFlags::IsFromDebugger);
@@ -1942,7 +1948,15 @@ class PatternBindingDecl final : public Decl,
   void setInitializerSubsumed(unsigned i) {
     getMutablePatternList()[i].setInitializerSubsumed();
   }
-  
+
+  bool isInitializerSynthesized(unsigned i) const {
+    return getPatternList()[i].isInitializerSynthesized();
+  }
+
+  void setInitializerSynthesized(unsigned i) {
+    getMutablePatternList()[i].setInitializerSynthesized();
+  }
+
   /// Does this binding declare something that requires storage?
   bool hasStorage() const;
 

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2159,12 +2159,23 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
         if (!DC->isLocalContext() &&
             !(PBD->getSingleVar() &&
               PBD->getSingleVar()->hasAttachedPropertyWrapper())) {
-          auto *initContext = cast_or_null<PatternBindingInitializer>(
-              PBD->getInitContext(i));
+          // Check whether `var` is a backing storage property and its
+          // initializer is already synthesized by storage check.
+          if (auto var = PBD->getSingleVar()) {
+            if (auto original = var->getOriginalWrappedProperty(
+                    PropertyWrapperSynthesizedPropertyKind::Backing)) {
+              auto parentPBD = original->getParentPatternBinding();
+              if (parentPBD->isInitializerSynthesized(i))
+                continue;
+            }
+          }
+          auto *initContext =
+              cast_or_null<PatternBindingInitializer>(PBD->getInitContext(i));
           if (initContext) {
             TypeChecker::contextualizeInitializer(initContext, init);
             checkInitializerActorIsolation(initContext, init);
             TypeChecker::checkInitializerEffects(initContext, init);
+            PBD->setInitializerSynthesized(0);
           }
         }
       }

lib/Sema/TypeCheckStorage.cpp

@@ -2982,6 +2982,7 @@ PropertyWrapperInitializerInfoRequest::evaluate(Evaluator &evaluator,
         typeCheckSynthesizedWrapperInitializer(var, defaultInit);
         parentPBD->setInit(0, defaultInit);
         parentPBD->setInitializerChecked(0);
+        parentPBD->setInitializerSynthesized(0);
       }
     }
 
@@ -3000,6 +3001,7 @@ PropertyWrapperInitializerInfoRequest::evaluate(Evaluator &evaluator,
         typeCheckSynthesizedWrapperInitializer(var, defaultInit);
         pbd->setInit(0, defaultInit);
         pbd->setInitializerChecked(0);
+        pbd->setInitializerSynthesized(0);
 
         // If a static, global, or local wrapped property has a default
         // initializer, this is the only initializer that will be used.

test/Sema/property_wrapper_parameter.swift

@@ -137,3 +137,14 @@ func takesWrapperClosure<T>(_: ProjectionWrapper<[S<T>]>, closure: (ProjectionWr
 func testGenericPropertyWrapper<U>(@ProjectionWrapper wrappers: [S<U>]) {
   takesWrapperClosure($wrappers) { $wrapper in }
 }
+
+@propertyWrapper
+public class SR_15940Bar<Value> {
+  public init(wrappedValue: @autoclosure () -> Value) {}
+  public var wrappedValue: Value {} // expected-error {{missing return in accessor expected to return 'Value'}}
+}
+
+// SR-15940
+class SR_15940 {
+  @SR_15940Bar var a: Bool?
+}