AST: Fix mangling of unvalidated declarations

This is again just a temporary workaround until getInterfaceType() can
kick off a request.

Author: slavapestov

lib/AST/ASTMangler.cpp

@@ -20,6 +20,7 @@
 #include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericSignature.h"
 #include "swift/AST/Initializer.h"
+#include "swift/AST/LazyResolver.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/Ownership.h"
 #include "swift/AST/ParameterList.h"
@@ -2323,6 +2324,12 @@ CanType ASTMangler::getDeclTypeForMangling(
   parentGenericSig = nullptr;
 
   auto &C = decl->getASTContext();
+  if (!decl->hasInterfaceType() && !decl->getDeclContext()->isLocalContext()) {
+    if (auto *resolver = C.getLazyResolver()) {
+      resolver->resolveDeclSignature(const_cast<ValueDecl *>(decl));
+    }
+  }
+
   if (!decl->hasInterfaceType() || decl->getInterfaceType()->is<ErrorType>()) {
     if (isa<AbstractFunctionDecl>(decl))
       return CanFunctionType::get({AnyFunctionType::Param(C.TheErrorType)},

test/IRGen/Inputs/vtable_multi_file_helper.swift

@@ -9,7 +9,7 @@ class SillySequence : Sequence, IteratorProtocol {
   var storedProperty: Int = 0
 
   func makeIterator() -> SillySequence {
-    return sel
+    return self
   }
 
   func next() -> Int? {
@@ -21,4 +21,8 @@ class Holder {
   func getSillySequence() -> SillySequence {
     return SillySequence()
   }
+}
+
+class Base {
+  func method() {}
 }

test/IRGen/vtable_multi_file.swift

@@ -2,6 +2,12 @@
 
 // REQUIRES: CPU=x86_64
 
+// CHECK-LABEL: @"$s17vtable_multi_file7DerivedCMf" = internal global
+// CHECK-SAME: @"$s17vtable_multi_file4BaseC6methodyyF"
+class Derived : Base {
+  func another() {}
+}
+
 func markUsed<T>(_ t: T) {}
 
 // CHECK-LABEL: define hidden swiftcc void @"$s17vtable_multi_file36baseClassVtablesIncludeImplicitInitsyyF"() {{.*}} {