[PropertyWrappers] When finding the initial value for the property, properly handle the situation where we have multiple attached property wrappers

If a property has multiple property wrappers attached, we'll have multiple nested calls, where each call's argument is a call to construct the next wrapper in the chain. However, when we use multiple wrappers consecutively, we cannot just rely on the call's type matching the innermost wrapper's type, because it will match the first wrapper in the sequence of consective wrappers and we'll end up crashing in SILGen. So, we should check if the call's argument is another call and look into that before checking the types.

Author: theblixguy

lib/AST/Decl.cpp

@@ -6127,13 +6127,25 @@ Expr *swift::findOriginalPropertyWrapperInitialValue(VarDecl *var,
         if (!call->isImplicit())
           return { true, E };
 
-        // ... producing a value of the same nominal type as the innermost
-        // property wrapper.
+        // ... which may call the constructor of another property
+        // wrapper if there are multiple wrappers attached to the
+        // property.
+        if (auto tuple = dyn_cast<TupleExpr>(call->getArg())) {
+          if (tuple->getNumElements() > 0) {
+            auto elem = tuple->getElement(0);
+            if (elem->isImplicit() && isa<CallExpr>(elem)) {
+              return { true, E };
+            }
+          }
+        }
+
+        // ... producing a value of the same nominal type as the
+        // innermost property wrapper.
         if (!call->getType() ||
             call->getType()->getAnyNominal() != innermostNominal)
-          return { true, E };
+          return { false, E };
 
-        // Find the implicit initialValue argument.
+        // Find the implicit initialValue/wrappedValue argument.
         if (auto tuple = dyn_cast<TupleExpr>(call->getArg())) {
           ASTContext &ctx = innermostNominal->getASTContext();
           for (unsigned i : range(tuple->getNumElements())) {

validation-test/compiler_crashers_2_fixed/sr10937.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-frontend -emit-sil %s
+
+@propertyWrapper
+struct Foo<T> {
+  init(wrappedValue: T) {
+    self.wrappedValue = wrappedValue
+  }
+
+  var wrappedValue: T
+}
+
+@propertyWrapper
+struct Bar<T> {
+  init(wrappedValue: T) {
+    self.wrappedValue = wrappedValue
+  }
+
+  var wrappedValue: T
+}
+
+struct Container {
+  @Foo @Foo var x: Int = 0
+  @Foo @Foo @Bar @Bar var y: Int = 1
+  @Foo @Bar @Foo @Foo var z: Int = 2
+}
+
+_ = Container()