[TypeChecker] Avoid checking lazy property accessors if they haven't been synthesized yet

Ttheir availability is going to match the property itself.
This is a workaround for lazy type-checking because synthesis
of accessors for such properties requires a reference to
`self` which won't be available because pattern binding
for the variable was skipped.

Resolves: rdar://129359362
Resolves: rdar://159463230
Resolves: swiftlang#84041

Author: xedin

lib/Sema/TypeCheckAvailability.cpp

@@ -2707,6 +2707,25 @@ class ExprAvailabilityWalker : public BaseDiagnosticWalker {
       return;
     }
 
+    // Avoid checking lazy property accessors if they haven't been
+    // synthesized yet, their availability is going to match the
+    // property itself. This is a workaround for lazy type-checking
+    // because synthesis of accessors for such properties requires
+    // a reference to `self` which won't be available because pattern
+    // binding for the variable was skipped.
+    //
+    // TODO: To fix this properly `getParentPatternBinding()`
+    // has to be refactored into a request to help establish association
+    // between a variable declaration and its pattern binding on demand
+    // instead of by using `typeCheckPatternBinding` called from the
+    // declaration checker.
+    if (D->getAttrs().hasAttribute<LazyAttr>()) {
+      auto *DC = D->getDeclContext();
+      if (DC->isTypeContext() && !(D->getAccessor(AccessorKind::Get) &&
+                                   D->getAccessor(AccessorKind::Set)))
+        return;
+    }
+
     DeclAvailabilityFlags flags;
     if (InInOutExpr)
       flags |= DeclAvailabilityFlag::ForInout;

test/Inputs/lazy_typecheck.swift

@@ -402,3 +402,7 @@ extension PublicStruct {
     lhs = rhs
   }
 }
+
+public class LazyPropertyWithClosureType {
+  public lazy var lazyVar: Int = { 2 }()
+}

test/Inputs/lazy_typecheck_client.swift

@@ -142,3 +142,8 @@ func testOperators() {
   var a: PublicStruct
   a <<< PublicStruct(x: 2)
 }
+
+func testLazyPropertyWithInitClosureReference(t: LazyPropertyWithClosureType) {
+  _ = t.lazyVar
+  t.lazyVar = 42
+}