--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/VFS/directory.c	Tue Jun 08 06:07:14 2021 +0900
@@ -0,0 +1,48 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/Underlying
+// RUN: mkdir -p %t/Overlay
+// RUN: mkdir -p %t/Middle
+// RUN: echo '// B.h in Underlying' > %t/Underlying/B.h
+// RUN: echo '#ifdef NESTED' >> %t/Underlying/B.h
+// RUN: echo '#include "C.h"' >> %t/Underlying/B.h
+// RUN: echo '#endif' >> %t/Underlying/B.h
+// RUN: echo '// C.h in Underlying' > %t/Underlying/C.h
+// RUN: echo '// C.h in Middle' > %t/Middle/C.h
+// RUN: echo '// C.h in Overlay' > %t/Overlay/C.h
+
+// 1) Underlying -> Overlay (C.h found, B.h falling back to Underlying)
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}/Overlay@g" -e "s@OUT_DIR@%{/t:regex_replacement}/Underlying@g" %S/Inputs/vfsoverlay-directory.yaml > %t/vfs.yaml
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=DIRECT %s
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -fsyntax-only -DNESTED -E -C %s 2>&1 | FileCheck --check-prefix=DIRECT %s
+// RUN: sed -e "s@INPUT_DIR@Overlay@g" -e "s@OUT_DIR@%{/t:regex_replacement}/Underlying@g" %S/Inputs/vfsoverlay-directory-relative.yaml > %t/vfs-relative.yaml
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs-relative.yaml -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=DIRECT %s
+
+// DIRECT: {{^}}// B.h in Underlying
+// DIRECT: {{^}}// C.h in Overlay
+
+// 2) Underlying -> Middle -> Overlay (C.h found, B.h falling back to Underlying)
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}/Overlay@g" -e "s@OUT_DIR@%{/t:regex_replacement}/Middle@g" %S/Inputs/vfsoverlay-directory.yaml > %t/vfs.yaml
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}/Middle@g" -e "s@OUT_DIR@%{/t:regex_replacement}/Underlying@g" %S/Inputs/vfsoverlay-directory.yaml > %t/vfs2.yaml
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -ivfsoverlay %t/vfs2.yaml -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=DIRECT %s
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -ivfsoverlay %t/vfs2.yaml -DNESTED -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=DIRECT %s
+
+// Same as direct above
+
+// 3) Underlying -> Middle -> Overlay (C.h falling back to Middle, B.h falling back to Underlying)
+// RUN: rm -f %t/Overlay/C.h
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -ivfsoverlay %t/vfs2.yaml -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=FALLBACK %s
+
+// FALLBACK: {{^}}// B.h in Underlying
+// FALLBACK: {{^}}// C.h in Middle
+
+// 3) Underlying -> Middle -> Overlay (C.h falling back to Underlying, B.h falling back to Underlying)
+// RUN: rm -f %t/Middle/C.h
+// RUN: %clang_cc1 -Werror -I %t/Underlying -ivfsoverlay %t/vfs.yaml -ivfsoverlay %t/vfs2.yaml -fsyntax-only -E -C %s 2>&1 | FileCheck --check-prefix=FALLBACK2 %s
+
+// FALLBACK2: {{^}}// B.h in Underlying
+// FALLBACK2: {{^}}// C.h in Underlying
+
+#include "B.h"
+#ifndef NESTED
+#include "C.h"
+#endif