[Sema] Fixes for mutability handling in property wrappers (swiftlang#76357)

Prevents a crash when a parameter references an invalid property wrapper. The original code assumed that mutability information would always be available, but this assumption fails when the property wrapper is invalid

Resolves swiftlang#65640

Author: janbaig

lib/Sema/TypeCheckStorage.cpp

@@ -2816,31 +2816,36 @@ static VarDecl *synthesizeLocalWrappedValueVar(VarDecl *var) {
   }
   Identifier name = ctx.getIdentifier(nameBuf);
 
-  VarDecl *localVar = new (ctx) VarDecl(/*IsStatic=*/false,
-                                        VarDecl::Introducer::Var,
-                                        var->getLoc(), name, dc);
-  localVar->setImplicit();
-  localVar->getAttrs() = var->getAttrs();
-  localVar->overwriteAccess(var->getFormalAccess());
-
+  std::optional<StorageImplInfo> mutability;
   if (var->hasImplicitPropertyWrapper()) {
     // FIXME: This can have a setter, but we need a resolved wrapper type
     // to figure it out.
-    localVar->setImplInfo(StorageImplInfo::getImmutableComputed());
+    mutability.emplace(StorageImplInfo::getImmutableComputed());
   } else {
-    auto mutability = *var->getPropertyWrapperMutability();
-    if (mutability.Getter == PropertyWrapperMutability::Mutating) {
+    auto possibleMutability = var->getPropertyWrapperMutability();
+    if (!possibleMutability)
+      return nullptr;
+
+    if (possibleMutability->Getter == PropertyWrapperMutability::Mutating) {
       ctx.Diags.diagnose(var->getLoc(), diag::property_wrapper_param_mutating);
       return nullptr;
     }
 
-    if (mutability.Setter == PropertyWrapperMutability::Nonmutating) {
-      localVar->setImplInfo(StorageImplInfo::getMutableComputed());
+    if (possibleMutability->Setter == PropertyWrapperMutability::Nonmutating) {
+      mutability.emplace(StorageImplInfo::getMutableComputed());
     } else {
-      localVar->setImplInfo(StorageImplInfo::getImmutableComputed());
+      mutability.emplace(StorageImplInfo::getImmutableComputed());
     }
   }
 
+  VarDecl *localVar = new (ctx) VarDecl(/*IsStatic=*/false,
+                                        VarDecl::Introducer::Var,
+                                        var->getLoc(), name, dc);
+  localVar->setImplicit();
+  localVar->getAttrs() = var->getAttrs();
+  localVar->overwriteAccess(var->getFormalAccess());
+  localVar->setImplInfo(*mutability);
+
   return localVar;
 }
 

validation-test/Sema/type_checker_crashers_fixed/issue-65640.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift -swift-version 5 -package-name myPkg
+
+// https://github.com/swiftlang/swift/issues/65640
+
+@propertyWrapper
+struct Wrapper {
+  // expected-error@-1{{property wrapper type 'Wrapper' does not contain a non-static property named 'wrappedValue'}}
+  init(wrappedValue: Int) {}
+}
+func test(@Wrapper x: Int) {}