[llvm][vfs] Make vfs::FileSystem::exists() virtual NFC (#88575)

Allow a `vfs::FileSystem` to provide a more efficient implementation of
`exists()` if they are able to. The existing `FileSystem`
implementations continue to default to using `status()` except that
overlay, proxy, and redirecting filesystems are taught to forward calls
to `exists()` correctly to their wrapped/external filesystem.

Co-authored-by: Ben Langmuir <blangmuir@apple.com>

1 files changed, 165 insertions, 0 deletions

diff --git a/llvm/unittests/Support/VirtualFileSystemTest.cpp b/llvm/unittests/Support/VirtualFileSystemTest.cpp
index 49a2e19..e9b4ac3 100644
--- a/llvm/unittests/Support/VirtualFileSystemTest.cpp
+++ b/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"));
+}