[llvm][vfs] Make vfs::FileSystem::exists() virtual NFC

llvm/include/llvm/Support/VirtualFileSystem.h

@@ -300,8 +300,9 @@ class FileSystem : public llvm::ThreadSafeRefCountedBase<FileSystem>,
   virtual std::error_code getRealPath(const Twine &Path,
                                       SmallVectorImpl<char> &Output);
 
-  /// Check whether a file exists. Provided for convenience.
-  bool exists(const Twine &Path);
+  /// Check whether \p Path exists. By default this uses \c status(), but
+  /// filesystems may provide a more efficient implementation if available.
+  virtual bool exists(const Twine &Path);
 
   /// Is the file mounted on a local filesystem?
   virtual std::error_code isLocal(const Twine &Path, bool &Result);
@@ -386,6 +387,7 @@ class OverlayFileSystem : public RTTIExtends<OverlayFileSystem, FileSystem> {
   void pushOverlay(IntrusiveRefCntPtr<FileSystem> FS);
 
   llvm::ErrorOr<Status> status(const Twine &Path) override;
+  bool exists(const Twine &Path) override;
   llvm::ErrorOr<std::unique_ptr<File>>
   openFileForRead(const Twine &Path) override;
   directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override;
@@ -439,6 +441,7 @@ class ProxyFileSystem : public RTTIExtends<ProxyFileSystem, FileSystem> {
   llvm::ErrorOr<Status> status(const Twine &Path) override {
     return FS->status(Path);
   }
+  bool exists(const Twine &Path) override { return FS->exists(Path); }
   llvm::ErrorOr<std::unique_ptr<File>>
   openFileForRead(const Twine &Path) override {
     return FS->openFileForRead(Path);
@@ -1044,6 +1047,7 @@ class RedirectingFileSystem
          bool UseExternalNames, FileSystem &ExternalFS);
 
   ErrorOr<Status> status(const Twine &Path) override;
+  bool exists(const Twine &Path) override;
   ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override;
 
   std::error_code getRealPath(const Twine &Path,

llvm/lib/Support/VirtualFileSystem.cpp

@@ -438,6 +438,15 @@ ErrorOr<Status> OverlayFileSystem::status(const Twine &Path) {
   return make_error_code(llvm::errc::no_such_file_or_directory);
 }
 
+bool OverlayFileSystem::exists(const Twine &Path) {
+  // FIXME: handle symlinks that cross file systems
+  for (iterator I = overlays_begin(), E = overlays_end(); I != E; ++I) {
+    if ((*I)->exists(Path))
+      return true;
+  }
+  return false;
+}
+
 ErrorOr<std::unique_ptr<File>>
 OverlayFileSystem::openFileForRead(const llvm::Twine &Path) {
   // FIXME: handle symlinks that cross file systems
@@ -2428,6 +2437,53 @@ ErrorOr<Status> RedirectingFileSystem::status(const Twine &OriginalPath) {
   return S;
 }
 
+bool RedirectingFileSystem::exists(const Twine &OriginalPath) {
+  SmallString<256> Path;
+  OriginalPath.toVector(Path);
+
+  if (makeAbsolute(Path))
+    return false;
+
+  if (Redirection == RedirectKind::Fallback) {
+    // Attempt to find the original file first, only falling back to the
+    // mapped file if that fails.
+    if (ExternalFS->exists(Path))
+      return true;
+  }
+
+  ErrorOr<RedirectingFileSystem::LookupResult> Result = lookupPath(Path);
+  if (!Result) {
+    // Was not able to map file, fallthrough to using the original path if
+    // that was the specified redirection type.
+    if (Redirection == RedirectKind::Fallthrough &&
+        isFileNotFound(Result.getError()))
+      return ExternalFS->exists(Path);
+    return false;
+  }
+
+  std::optional<StringRef> ExtRedirect = Result->getExternalRedirect();
+  if (!ExtRedirect) {
+    assert(isa<RedirectingFileSystem::DirectoryEntry>(Result->E));
+    return true;
+  }
+
+  SmallString<256> RemappedPath((*ExtRedirect).str());
+  if (makeAbsolute(RemappedPath))
+    return false;
+
+  if (ExternalFS->exists(RemappedPath))
+    return true;
+
+  if (Redirection == RedirectKind::Fallthrough) {
+    // Mapped the file but it wasn't found in the underlying filesystem,
+    // fallthrough to using the original path if that was the specified
+    // redirection type.
+    return ExternalFS->exists(Path);
+  }
+
+  return false;
+}
+
 namespace {
 
 /// Provide a file wrapper with an overriden status.

llvm/unittests/Support/VirtualFileSystemTest.cpp

@@ -201,6 +201,21 @@ class ErrorDummyFileSystem : public DummyFileSystem {
   }
 };
 
+/// A version of \c DummyFileSystem that aborts on \c status() to test that
+/// \c exists() is being used.
+class NoStatusDummyFileSystem : public DummyFileSystem {
+public:
+  ErrorOr<vfs::Status> status(const Twine &Path) override {
+    llvm::report_fatal_error(
+        "unexpected call to NoStatusDummyFileSystem::status");
+  }
+
+  bool exists(const Twine &Path) override {
+    auto Status = DummyFileSystem::status(Path);
+    return Status && Status->exists();
+  }
+};
+
 /// Replace back-slashes by front-slashes.
 std::string getPosixPath(const Twine &S) {
   SmallString<128> Result;
@@ -968,6 +983,30 @@ TEST(OverlayFileSystemTest, PrintOutput) {
             Output);
 }
 
+TEST(OverlayFileSystemTest, Exists) {
+  IntrusiveRefCntPtr<DummyFileSystem> Lower(new NoStatusDummyFileSystem());
+  IntrusiveRefCntPtr<DummyFileSystem> Upper(new NoStatusDummyFileSystem());
+  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+      new vfs::OverlayFileSystem(Lower));
+  O->pushOverlay(Upper);
+
+  Lower->addDirectory("/both");
+  Upper->addDirectory("/both");
+  Lower->addRegularFile("/both/lower_file");
+  Upper->addRegularFile("/both/upper_file");
+  Lower->addDirectory("/lower");
+  Upper->addDirectory("/upper");
+
+  EXPECT_TRUE(O->exists("/both"));
+  EXPECT_TRUE(O->exists("/both"));
+  EXPECT_TRUE(O->exists("/both/lower_file"));
+  EXPECT_TRUE(O->exists("/both/upper_file"));
+  EXPECT_TRUE(O->exists("/lower"));
+  EXPECT_TRUE(O->exists("/upper"));
+  EXPECT_FALSE(O->exists("/both/nope"));
+  EXPECT_FALSE(O->exists("/nope"));
+}
+
 TEST(ProxyFileSystemTest, Basic) {
   IntrusiveRefCntPtr<vfs::InMemoryFileSystem> Base(
       new vfs::InMemoryFileSystem());
@@ -3364,6 +3403,11 @@ TEST(RedirectingFileSystemTest, ExternalPaths) {
       SeenPaths.push_back(Dir.str());
       return ProxyFileSystem::dir_begin(Dir, EC);
     }
+
+    bool exists(const Twine &Path) override {
+      SeenPaths.push_back(Path.str());
+      return ProxyFileSystem::exists(Path);
+    }
   };
 
   std::error_code EC;
@@ -3395,3 +3439,124 @@ TEST(RedirectingFileSystemTest, ExternalPaths) {
 
   EXPECT_EQ(CheckFS->SeenPaths, Expected);
 }
+
+TEST(RedirectingFileSystemTest, Exists) {
+  IntrusiveRefCntPtr<DummyFileSystem> Dummy(new NoStatusDummyFileSystem());
+  auto YAML =
+    MemoryBuffer::getMemBuffer("{\n"
+                               "  'version': 0,\n"
+                               "  'roots': [\n"
+                               "    {\n"
+                               "      'type': 'directory-remap',\n"
+                               "      'name': '/dremap',\n"
+                               "      'external-contents': '/a',\n"
+                               "    },"
+                               "    {\n"
+                               "      'type': 'directory-remap',\n"
+                               "      'name': '/dmissing',\n"
+                               "      'external-contents': '/dmissing',\n"
+                               "    },"
+                               "    {\n"
+                               "      'type': 'directory',\n"
+                               "      'name': '/both',\n"
+                               "      'contents': [\n"
+                               "        {\n"
+                               "          'type': 'file',\n"
+                               "          'name': 'vfile',\n"
+                               "          'external-contents': '/c'\n"
+                               "        }\n"
+                               "      ]\n"
+                               "    },\n"
+                               "    {\n"
+                               "      'type': 'directory',\n"
+                               "      'name': '/vdir',\n"
+                               "      'contents': ["
+                               "        {\n"
+                               "          'type': 'directory-remap',\n"
+                               "          'name': 'dremap',\n"
+                               "          'external-contents': '/b'\n"
+                               "        },\n"
+                               "        {\n"
+                               "          'type': 'file',\n"
+                               "          'name': 'missing',\n"
+                               "          'external-contents': '/missing'\n"
+                               "        },\n"
+                               "        {\n"
+                               "          'type': 'file',\n"
+                               "          'name': 'vfile',\n"
+                               "          'external-contents': '/c'\n"
+                               "        }]\n"
+                               "    }]\n"
+                               "}");
+
+  Dummy->addDirectory("/a");
+  Dummy->addRegularFile("/a/foo");
+  Dummy->addDirectory("/b");
+  Dummy->addRegularFile("/c");
+  Dummy->addRegularFile("/both/foo");
+
+  auto Redirecting = vfs::RedirectingFileSystem::create(
+							std::move(YAML), nullptr, "", nullptr, Dummy);
+
+  EXPECT_TRUE(Redirecting->exists("/dremap"));
+  EXPECT_FALSE(Redirecting->exists("/dmissing"));
+  EXPECT_FALSE(Redirecting->exists("/unknown"));
+  EXPECT_TRUE(Redirecting->exists("/both"));
+  EXPECT_TRUE(Redirecting->exists("/both/foo"));
+  EXPECT_TRUE(Redirecting->exists("/both/vfile"));
+  EXPECT_TRUE(Redirecting->exists("/vdir"));
+  EXPECT_TRUE(Redirecting->exists("/vdir/dremap"));
+  EXPECT_FALSE(Redirecting->exists("/vdir/missing"));
+  EXPECT_TRUE(Redirecting->exists("/vdir/vfile"));
+  EXPECT_FALSE(Redirecting->exists("/vdir/unknown"));
+}
+
+TEST(RedirectingFileSystemTest, ExistsFallback) {
+  IntrusiveRefCntPtr<DummyFileSystem> Dummy(new NoStatusDummyFileSystem());
+  auto YAML =
+    MemoryBuffer::getMemBuffer("{\n"
+                               "  'version': 0,\n"
+                               "  'redirecting-with': 'fallback',\n"
+                               "  'roots': [\n"
+                               "    {\n"
+                               "      'type': 'file',\n"
+                               "      'name': '/fallback',\n"
+                               "      'external-contents': '/missing',\n"
+                               "    },"
+                               "  ]\n"
+                               "}");
+
+  Dummy->addRegularFile("/fallback");
+
+  auto Redirecting = vfs::RedirectingFileSystem::create(
+							std::move(YAML), nullptr, "", nullptr, Dummy);
+
+  EXPECT_TRUE(Redirecting->exists("/fallback"));
+  EXPECT_FALSE(Redirecting->exists("/missing"));
+}
+
+TEST(RedirectingFileSystemTest, ExistsRedirectOnly) {
+  IntrusiveRefCntPtr<DummyFileSystem> Dummy(new NoStatusDummyFileSystem());
+  auto YAML =
+    MemoryBuffer::getMemBuffer("{\n"
+                               "  'version': 0,\n"
+                               "  'redirecting-with': 'redirect-only',\n"
+                               "  'roots': [\n"
+                               "    {\n"
+                               "      'type': 'file',\n"
+                               "      'name': '/vfile',\n"
+                               "      'external-contents': '/a',\n"
+                               "    },"
+                               "  ]\n"
+                               "}");
+
+  Dummy->addRegularFile("/a");
+  Dummy->addRegularFile("/b");
+
+  auto Redirecting = vfs::RedirectingFileSystem::create(
+							std::move(YAML), nullptr, "", nullptr, Dummy);
+
+  EXPECT_FALSE(Redirecting->exists("/a"));
+  EXPECT_FALSE(Redirecting->exists("/b"));
+  EXPECT_TRUE(Redirecting->exists("/vfile"));
+}