[cxx-interop] Fix test for linux; bail if we didn't load the overlay.

Author: zoecarver

lib/Sema/CSDiagnostics.cpp

@@ -3767,6 +3767,10 @@ void MissingMemberFailure::diagnoseUnsafeCxxMethod(SourceLoc loc,
     auto conformsToRACollection = [&](auto baseType) {
       auto raCollectionProto =
           ctx.getProtocol(KnownProtocolKind::CxxRandomAccessCollection);
+      // We didn't load the overlay.
+      if (raCollectionProto == nullptr)
+        return false;
+
       SmallVector<ProtocolConformance *, 2> scratch;
       return baseType->getAnyNominal()->lookupConformance(raCollectionProto,
                                                           scratch);

test/Interop/Cxx/class/fixits-for-std-vector.swift

@@ -1,10 +1,9 @@
-// TODO: why can't we run this on linux?
-// REQUIRES: OS=macosx
-
 // RUN: rm -rf %t
 // RUN: split-file %s %t
 // RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop 2>&1 | %FileCheck %s
 
+// REQUIRES: OS=macosx || OS=linux-gnu
+
 //--- Inputs/module.modulemap
 module Test {
     header "test.h"
@@ -19,7 +18,7 @@ using V = std::vector<int>;
 //--- test.swift
 
 import Test
-import CxxStdlib.vector
+import CxxStdlib
 
 public func test(v: V) {
   // CHECK: note: C++ method 'begin' that returns an iterator is unavailable