[CodeSynthesis] Make sure that LazyInitializerExpr has a type

Currently when `LazyInitializerExpr` is added to the AST it's not
given an explicit type. Because of that constraint solver silently
fails in contraint generator without diagnostic. But since
sub-expression associated with `LazyInitializerExpr` is already
type-checked it makes sense to set its type explicitly.

Author: xedin

lib/Sema/CSApply.cpp

@@ -3885,8 +3885,8 @@ namespace {
     }
 
     Expr *visitLazyInitializerExpr(LazyInitializerExpr *expr) {
-      simplifyExprType(expr);
-      assert(expr->getType()->isEqual(expr->getSubExpr()->getType()));
+      expr = simplifyExprType(expr);
+      assert(cs.getType(expr)->isEqual(expr->getSubExpr()->getType()));
       return expr;
     }
 

lib/Sema/CSGen.cpp

@@ -2918,7 +2918,9 @@ namespace {
     }
 
     Type visitLazyInitializerExpr(LazyInitializerExpr *expr) {
-      return expr->getType();
+      auto type = expr->getType();
+      assert(type && "LazyInitializerExpr should always have type set");
+      return type;
     }
 
     Type visitEditorPlaceholderExpr(EditorPlaceholderExpr *E) {

lib/Sema/CodeSynthesis.cpp

@@ -1294,7 +1294,9 @@ static void synthesizeLazyGetterBody(AbstractFunctionDecl *fn, void *context) {
   // FIXME: we should really have stronger invariants than this.  Leaving it
   // unwrapped may expose both expressions to naive walkers
   if (wasInitializerChecked) {
+    auto initType = InitValue->getType();
     InitValue = new (Ctx) LazyInitializerExpr(InitValue);
+    InitValue->setType(initType);
   }
 
   Pattern *Tmp2PBDPattern = new (Ctx) NamedPattern(Tmp2VD, /*implicit*/true);