Do not type check lazy accessor bodies eagerly.

Start chipping away at cross-file type checker performance issues by
avoiding type checking of lazy property accessor bodies when the type in
question is defined in a different file and the lazy property is a typed
pattern.

We still type check these in the file they are defined in when we go to
type check the types defined within that file.

Resolves rdar://problem/26894118.

Author: rudkx

lib/Sema/CodeSynthesis.cpp

@@ -1625,6 +1625,7 @@ void TypeChecker::completeLazyVarImplementation(VarDecl *VD) {
 
   // Now that we've got the storage squared away, synthesize the getter.
   auto *Get = completeLazyPropertyGetter(VD, Storage, *this);
+  validateDecl(Get);
 
   // The setter just forwards on to storage without materializing the initial
   // value.
@@ -1643,12 +1644,6 @@ void TypeChecker::completeLazyVarImplementation(VarDecl *VD) {
   Storage->setImplicit();
   Storage->setAccessibility(Accessibility::Private);
   Storage->setSetterAccessibility(Accessibility::Private);
-
-  typeCheckDecl(Get, true);
-  typeCheckDecl(Get, false);
-
-  typeCheckDecl(Set, true);
-  typeCheckDecl(Set, false);
 }
 
 

test/Sema/Inputs/forbid_typecheck_2.swift

@@ -8,4 +8,5 @@ class NOTYPECHECK_cls {}
 
 class ClsSec {
   let member : Int = NOTYPECHECK_member
+  lazy var lazymember: Int = NOTYPECHECK_lazymember
 }