[VFS] Add property 'fallthrough' that controls fallback to real file …

…system.

Default property value 'true' preserves current behavior. Value 'false' can be
used to create VFS "root", file system that gives better control over which
files compiler can use during compilation as there are no unpredictable
accesses to real file system.

Non-fallthrough use case changes how we treat multiple VFS overlay
files. Instead of all of them being at the same level just above a real
file system, now they are nested and subsequent overlays can refer to
files in previous overlays.

Change is done both in LLVM and Clang, corresponding LLVM commit is r345431.

rdar://problem/39465552

Reviewers: bruno, benlangmuir

Reviewed By: bruno

Subscribers: dexonsmith, cfe-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D50539

llvm-svn: 345432

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3297,25 +3297,27 @@ IntrusiveRefCntPtr<llvm::vfs::FileSystem> createVFSFromCompilerInvocation(
   if (CI.getHeaderSearchOpts().VFSOverlayFiles.empty())
     return BaseFS;
 
-  IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem> Overlay(
-      new llvm::vfs::OverlayFileSystem(BaseFS));
+  IntrusiveRefCntPtr<llvm::vfs::FileSystem> Result = BaseFS;
   // earlier vfs files are on the bottom
   for (const auto &File : CI.getHeaderSearchOpts().VFSOverlayFiles) {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
-        BaseFS->getBufferForFile(File);
+        Result->getBufferForFile(File);
     if (!Buffer) {
       Diags.Report(diag::err_missing_vfs_overlay_file) << File;
       continue;
     }
 
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS = llvm::vfs::getVFSFromYAML(
-        std::move(Buffer.get()), /*DiagHandler*/ nullptr, File);
-    if (FS)
-      Overlay->pushOverlay(FS);
-    else
+        std::move(Buffer.get()), /*DiagHandler*/ nullptr, File,
+        /*DiagContext*/ nullptr, Result);
+    if (!FS) {
       Diags.Report(diag::err_invalid_vfs_overlay) << File;
+      continue;
+    }
+
+    Result = FS;
   }
-  return Overlay;
+  return Result;
 }
 
 } // namespace clang

clang/test/VFS/Inputs/Broken.framework/Headers/Error.h

@@ -0,0 +1,3 @@
+// Error.h
+
+#error Should not include this header in a module

clang/test/VFS/Inputs/Broken.framework/Modules/module.modulemap

@@ -0,0 +1,6 @@
+framework module Broken [extern_c] {
+  umbrella "Headers"
+  export *
+  module * { export * }
+}
+

clang/test/VFS/Inputs/Broken.framework/VFSHeaders/A.h

@@ -0,0 +1 @@
+// A.h

clang/test/VFS/Inputs/vfsroot.yaml

@@ -0,0 +1,55 @@
+{
+  'version': 0,
+  'use-external-names': false,
+  'fallthrough': false,
+  'roots': [
+    { 'name': '/tests', 'type': 'directory',
+      'contents': [
+        { 'name': 'vfsroot-include.c', 'type': 'file',
+          'external-contents': 'TEST_DIR/vfsroot-include.c'
+        },
+        { 'name': 'vfsroot-with-overlay.c', 'type': 'file',
+          'external-contents': 'TEST_DIR/vfsroot-with-overlay.c'
+        },
+        { 'name': 'vfsroot-module.m', 'type': 'file',
+          'external-contents': 'TEST_DIR/vfsroot-module.m'
+        }
+      ]
+    },
+    { 'name': '/direct-vfs-root-files', 'type': 'directory',
+      'contents': [
+        { 'name': 'not_real.h', 'type': 'file',
+          'external-contents': 'TEST_DIR/Inputs/actual_header.h'
+        },
+        { 'name': 'vfsoverlay.yaml', 'type': 'file',
+          'external-contents': 'OUT_DIR/vfsoverlay.yaml'
+        }
+      ]
+    },
+    { 'name': '/indirect-vfs-root-files', 'type': 'directory',
+      'contents': [
+        { 'name': 'actual_header.h', 'type': 'file',
+          'external-contents': 'TEST_DIR/Inputs/actual_header.h'
+        }
+      ]
+    },
+    { 'name': 'TEST_DIR/Inputs/Broken.framework', 'type': 'directory',
+      'contents': [
+        { 'name': 'Headers/A.h', 'type': 'file',
+          'external-contents': 'TEST_DIR/Inputs/Broken.framework/VFSHeaders/A.h'
+        },
+        { 'name': 'Modules/module.modulemap', 'type': 'file',
+          'external-contents': 'TEST_DIR/Inputs/Broken.framework/Modules/module.modulemap'
+        }
+      ]
+    },
+    # Locations for modules.
+    { 'name': 'OUT_DIR/cache', 'type': 'directory',
+      'contents': [
+        { 'name': 'Broken.pcm', 'type': 'file',
+          'external-contents': 'OUT_DIR/cache/Broken.pcm'
+        }
+      ]
+    }
+  ]
+}

clang/test/VFS/vfsroot-include.c

@@ -0,0 +1,17 @@
+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: sed -e "s:TEST_DIR:%S:g" -e "s:OUT_DIR:%t:g" %S/Inputs/vfsroot.yaml > %t.yaml
+// RUN: not %clang_cc1 -Werror -ivfsoverlay %t.yaml -I %S/Inputs -I /direct-vfs-root-files -fsyntax-only /tests/vfsroot-include.c 2>&1 | FileCheck %s
+// The line above tests that the compiler input file is looked up through VFS.
+
+// Test successful include through the VFS.
+#include "not_real.h"
+
+// Test that a file missing from the VFS root is not found, even if it is
+// discoverable through the real file system. Fatal error should be the last
+// in the file as it hides other errors.
+#include "actual_header.h"
+// CHECK: fatal error: 'actual_header.h' file not found
+// CHECK: 1 error generated.
+// CHECK-NOT: error

clang/test/VFS/vfsroot-module.m

@@ -0,0 +1,10 @@
+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: sed -e "s:TEST_DIR:%S:g" -e "s:OUT_DIR:%t:g" %S/Inputs/vfsroot.yaml > %t.yaml
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fdisable-module-hash -fmodules-cache-path=%t/cache -ivfsoverlay %t.yaml -F %S/Inputs -fsyntax-only /tests/vfsroot-module.m
+
+// Test that a file missing from the VFS root is not found, even if it is
+// discoverable through the real file system at location that is a part of
+// the framework.
+@import Broken;

clang/test/VFS/vfsroot-with-overlay.c

@@ -0,0 +1,12 @@
+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: sed -e "s:TEST_DIR:%S:g" -e "s:OUT_DIR:%t:g" %S/Inputs/vfsroot.yaml > %t.yaml
+// RUN: sed -e "s:INPUT_DIR:/indirect-vfs-root-files:g" -e "s:OUT_DIR:/overlay-dir:g" %S/Inputs/vfsoverlay.yaml > %t/vfsoverlay.yaml
+// RUN: %clang_cc1 -Werror -ivfsoverlay %t.yaml -ivfsoverlay /direct-vfs-root-files/vfsoverlay.yaml -I /overlay-dir -fsyntax-only /tests/vfsroot-with-overlay.c
+
+#include "not_real.h"
+
+void foo() {
+  bar();
+}