[lldb/Support] Treat empty FileSpec as an invalid file.

LLDB relies on empty FileSpecs being invalid files, for example, they
don't exists. Currently this assumption does not always hold during
reproducer replay, because we pass the result of GetPath to the VFS.
This is an empty string, which the VFS converts to an absolute directory
by prepending the current working directory, before looking it up in the
YAML mapping. This means that an empty FileSpec will exist when the
current working directory does. This breaks at least one test
(TestAddDsymCommand.py) when ran from replay.

This patch special cases empty FileSpecs and returns a sensible result
before calling GetPath and forwarding the call.

Differential revision: https://reviews.llvm.org/D77351

lldb/source/Host/common/FileSystem.cpp

@@ -87,6 +87,11 @@ Optional<FileSystem> &FileSystem::InstanceImpl() {
 
 vfs::directory_iterator FileSystem::DirBegin(const FileSpec &file_spec,
                                              std::error_code &ec) {
+  if (!file_spec) {
+    ec = std::error_code(static_cast<int>(errc::no_such_file_or_directory),
+                         std::system_category());
+    return {};
+  }
   return DirBegin(file_spec.GetPath(), ec);
 }
 
@@ -97,6 +102,9 @@ vfs::directory_iterator FileSystem::DirBegin(const Twine &dir,
 
 llvm::ErrorOr<vfs::Status>
 FileSystem::GetStatus(const FileSpec &file_spec) const {
+  if (!file_spec)
+    return std::error_code(static_cast<int>(errc::no_such_file_or_directory),
+                           std::system_category());
   return GetStatus(file_spec.GetPath());
 }
 
@@ -106,6 +114,8 @@ llvm::ErrorOr<vfs::Status> FileSystem::GetStatus(const Twine &path) const {
 
 sys::TimePoint<>
 FileSystem::GetModificationTime(const FileSpec &file_spec) const {
+  if (!file_spec)
+    return sys::TimePoint<>();
   return GetModificationTime(file_spec.GetPath());
 }
 
@@ -117,6 +127,8 @@ sys::TimePoint<> FileSystem::GetModificationTime(const Twine &path) const {
 }
 
 uint64_t FileSystem::GetByteSize(const FileSpec &file_spec) const {
+  if (!file_spec)
+    return 0;
   return GetByteSize(file_spec.GetPath());
 }
 
@@ -133,6 +145,8 @@ uint32_t FileSystem::GetPermissions(const FileSpec &file_spec) const {
 
 uint32_t FileSystem::GetPermissions(const FileSpec &file_spec,
                                     std::error_code &ec) const {
+  if (!file_spec)
+    return sys::fs::perms::perms_not_known;
   return GetPermissions(file_spec.GetPath(), ec);
 }
 
@@ -154,7 +168,7 @@ uint32_t FileSystem::GetPermissions(const Twine &path,
 bool FileSystem::Exists(const Twine &path) const { return m_fs->exists(path); }
 
 bool FileSystem::Exists(const FileSpec &file_spec) const {
-  return Exists(file_spec.GetPath());
+  return file_spec && Exists(file_spec.GetPath());
 }
 
 bool FileSystem::Readable(const Twine &path) const {
@@ -162,7 +176,7 @@ bool FileSystem::Readable(const Twine &path) const {
 }
 
 bool FileSystem::Readable(const FileSpec &file_spec) const {
-  return Readable(file_spec.GetPath());
+  return file_spec && Readable(file_spec.GetPath());
 }
 
 bool FileSystem::IsDirectory(const Twine &path) const {
@@ -173,7 +187,7 @@ bool FileSystem::IsDirectory(const Twine &path) const {
 }
 
 bool FileSystem::IsDirectory(const FileSpec &file_spec) const {
-  return IsDirectory(file_spec.GetPath());
+  return file_spec && IsDirectory(file_spec.GetPath());
 }
 
 bool FileSystem::IsLocal(const Twine &path) const {
@@ -183,7 +197,7 @@ bool FileSystem::IsLocal(const Twine &path) const {
 }
 
 bool FileSystem::IsLocal(const FileSpec &file_spec) const {
-  return IsLocal(file_spec.GetPath());
+  return file_spec && IsLocal(file_spec.GetPath());
 }
 
 void FileSystem::EnumerateDirectory(Twine path, bool find_directories,
@@ -261,6 +275,9 @@ void FileSystem::Resolve(SmallVectorImpl<char> &path) {
 }
 
 void FileSystem::Resolve(FileSpec &file_spec) {
+  if (!file_spec)
+    return;
+
   // Extract path from the FileSpec.
   SmallString<128> path;
   file_spec.GetPath(path);

lldb/unittests/Host/FileSystemTest.cpp

@@ -303,3 +303,29 @@ TEST(FileSystemTest, OpenErrno) {
   EXPECT_EQ(code.value(), ENOENT);
 }
 
+TEST(FileSystemTest, EmptyTest) {
+  FileSpec spec;
+  FileSystem fs;
+
+  {
+    std::error_code ec;
+    fs.DirBegin(spec, ec);
+    EXPECT_EQ(ec.category(), std::system_category());
+    EXPECT_EQ(ec.value(), ENOENT);
+  }
+
+  {
+    llvm::ErrorOr<vfs::Status> status = fs.GetStatus(spec);
+    ASSERT_FALSE(status);
+    EXPECT_EQ(status.getError().category(), std::system_category());
+    EXPECT_EQ(status.getError().value(), ENOENT);
+  }
+
+  EXPECT_EQ(sys::TimePoint<>(), fs.GetModificationTime(spec));
+  EXPECT_EQ(static_cast<uint64_t>(0), fs.GetByteSize(spec));
+  EXPECT_EQ(llvm::sys::fs::perms::perms_not_known, fs.GetPermissions(spec));
+  EXPECT_FALSE(fs.Exists(spec));
+  EXPECT_FALSE(fs.Readable(spec));
+  EXPECT_FALSE(fs.IsDirectory(spec));
+  EXPECT_FALSE(fs.IsLocal(spec));
+}