[llvm] Use the VFS to make path absolute

Author: jansvoboda11

llvm/lib/Support/VirtualFileSystem.cpp

@@ -2204,7 +2204,7 @@ RedirectingFileSystem::create(std::unique_ptr<MemoryBuffer> Buffer,
     //  FS->OverlayFileDir => /<absolute_path_to>/dummy.cache/vfs
     //
     SmallString<256> OverlayAbsDir = sys::path::parent_path(YAMLFilePath);
-    std::error_code EC = llvm::sys::fs::make_absolute(OverlayAbsDir);
+    std::error_code EC = ExternalFS->makeAbsolute(OverlayAbsDir);
     assert(!EC && "Overlay dir final path must be absolute");
     (void)EC;
     FS->setOverlayFileDir(OverlayAbsDir);

llvm/unittests/Support/VirtualFileSystemTest.cpp

@@ -1941,6 +1941,29 @@ TEST_F(VFSFromYAMLTest, ReturnsExternalPathVFSHit) {
   EXPECT_EQ(0, NumDiagnostics);
 }
 
+TEST_F(VFSFromYAMLTest, RelativeFileDirWithOverlayRelativeSetting) {
+  auto Lower = makeIntrusiveRefCnt<DummyFileSystem>();
+  Lower->addDirectory("//root/foo/bar");
+  Lower->addRegularFile("//root/foo/bar/a");
+  Lower->setCurrentWorkingDirectory("//root/foo");
+  IntrusiveRefCntPtr<vfs::FileSystem> FS =
+      getFromYAMLString("{\n"
+                        "  'case-sensitive': false,\n"
+                        "  'overlay-relative': true,\n"
+                        "  'roots': [\n"
+                        "    { 'name': '//root/foo/bar/b', 'type': 'file',\n"
+                        "      'external-contents': 'a'\n"
+                        "    }\n"
+                        "  ]\n"
+                        "}",
+                        Lower, "bar/overlay");
+
+  ASSERT_NE(FS.get(), nullptr);
+  ErrorOr<vfs::Status> S = FS->status("//root/foo/bar/b");
+  ASSERT_FALSE(S.getError());
+  EXPECT_EQ("//root/foo/bar/a", S->getName());
+}
+
 TEST_F(VFSFromYAMLTest, RootRelativeToOverlayDirTest) {
   auto Lower = makeIntrusiveRefCnt<DummyFileSystem>();
   Lower->addDirectory("//root/foo/bar");