[Type checker] Fix multi-file crasher for property wrapper backing storage.

Fixes rdar://problem/51810057

Author: DougGregor

lib/Sema/CodeSynthesis.cpp

@@ -1721,6 +1721,11 @@ PropertyWrapperBackingPropertyInfoRequest::evaluate(Evaluator &evaluator,
   Type storageInterfaceType = wrapperType;
   Type storageType = dc->mapTypeIntoContext(storageInterfaceType);
 
+  if (!var->hasInterfaceType()) {
+    auto &tc = *static_cast<TypeChecker *>(ctx.getLazyResolver());
+    tc.validateDecl(var);
+  }
+
   // Make sure that the property type matches the value of the
   // wrapper type.
   if (!storageInterfaceType->hasError()) {
@@ -1771,9 +1776,6 @@ PropertyWrapperBackingPropertyInfoRequest::evaluate(Evaluator &evaluator,
   if (parentPBD->isInitialized(patternNumber) &&
       !parentPBD->isInitializerChecked(patternNumber)) {
     auto &tc = *static_cast<TypeChecker *>(ctx.getLazyResolver());
-    if (!var->hasType())
-      tc.validateDecl(var);
-
     tc.typeCheckPatternBinding(parentPBD, patternNumber);
   }
 

test/multifile/Inputs/sr10933a.swift

@@ -0,0 +1,14 @@
+@propertyWrapper
+class Wrapper<T> {
+  private var _value: T
+  
+  var wrappedValue: T {
+    get { _value }
+    set { _value = newValue }
+  }
+  
+  init(defaultValue: T) {
+    self._value = defaultValue
+  }
+  
+}

test/multifile/Inputs/sr10933b.swift

@@ -0,0 +1,8 @@
+@propertyWrapper
+final class IntWrapper: Wrapper<Int> {
+  override var value: Int {
+    get { super.value }
+    set { super.value = newValue }
+  }
+}
+

test/multifile/property-wrappers-sr10933.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-frontend -typecheck -primary-file %s %S/Inputs/sr10933a.swift %S/Inputs/sr10933b.swift
+
+// SR-10933: crash involving multiple files
+class Holder {
+  @IntWrapper(defaultValue: 100) var int: Int
+}
+
+func main() {
+  let h = Holder()
+}