[AST] Properties can be explicitly initialized via their wrapper.

The computation for "is explicitly initialized" on a pattern binding
entry didn't account for explicit initialization via the property
wrapper (e.g. @wrapper(closure: { ... })), which lead to a crash for
properties with optional type. Fixes rdar://problem/57411331.

Author: DougGregor

include/swift/AST/Decl.h

@@ -1889,7 +1889,10 @@ class PatternBindingEntry {
   void setPattern(Pattern *P) { PatternAndFlags.setPointer(P); }
 
   /// Whether the given pattern binding entry is initialized.
-  bool isInitialized() const;
+  ///
+  /// \param onlyExplicit Only consider explicit initializations (rather
+  /// than implicitly-generated ones).
+  bool isInitialized(bool onlyExplicit = false) const;
 
   Expr *getInit() const {
     if (PatternAndFlags.getInt().contains(Flags::Removed) ||

lib/AST/Decl.cpp

@@ -1539,9 +1539,9 @@ void PatternBindingEntry::setOriginalInit(Expr *E) {
                              PatternFlags::IsText);
 }
 
-bool PatternBindingEntry::isInitialized() const {
+bool PatternBindingEntry::isInitialized(bool onlyExplicit) const {
   // Directly initialized.
-  if (getInit())
+  if (getInit() && (!onlyExplicit || getEqualLoc().isValid()))
     return true;
 
   // Initialized via a property wrapper.
@@ -1833,7 +1833,7 @@ bool PatternBindingDecl::isComputingPatternBindingEntry(
 
 bool PatternBindingDecl::isExplicitlyInitialized(unsigned i) const {
   const auto &entry = getPatternList()[i];
-  return entry.isInitialized() && entry.getEqualLoc().isValid();
+  return entry.isInitialized(/*onlyExplicit=*/true);
 }
 
 SourceLoc PatternBindingDecl::getEqualLoc(unsigned i) const {

test/decl/var/property_wrappers.swift

@@ -1809,3 +1809,25 @@ func test_rdar56350060() {
     }
   }
 }
+
+// rdar://problem/57411331 - crash due to incorrectly synthesized "nil" default
+// argument.
+@propertyWrapper
+struct Blah<Value> {
+  init(blah _: Int) { }
+
+  var wrappedValue: Value {
+    let val: Value? = nil
+    return val!
+  }
+}
+
+struct UseRdar57411331 {
+  let x = Rdar57411331(other: 5)
+}
+
+struct Rdar57411331 {
+  @Blah(blah: 17) var something: Int?
+
+  var other: Int
+}