Add FileName::Resolve

Author: phst

elisp/private/tools/system.cc

@@ -486,6 +486,42 @@ absl::StatusOr<FileName> FileName::MakeRelative(const FileName& base) const {
   return FileName::FromString(rel);
 }
 
+absl::StatusOr<FileName> FileName::Resolve() const {
+#ifdef _WIN32
+  constexpr DWORD access = 0;
+  constexpr DWORD share = 0;
+  constexpr DWORD disposition = OPEN_EXISTING;
+  constexpr DWORD open_flags = FILE_FLAG_BACKUP_SEMANTICS;
+  const HANDLE handle = ::CreateFileW(this->pointer(), access, share, nullptr,
+                                      disposition, open_flags, nullptr);
+  if (handle == INVALID_HANDLE_VALUE) {
+    return WindowsStatus("CreateFileW", absl::Hex(access), absl::Hex(share),
+                         nullptr, disposition, absl::Hex(open_flags), nullptr);
+  }
+  const absl::Cleanup cleanup = [handle] {
+    if (!::CloseHandle(handle)) LOG(ERROR) << WindowsStatus("CloseHandle");
+  };
+  std::array<wchar_t, 0x8000> buffer;
+  constexpr DWORD name_flags = FILE_NAME_NORMALIZED | VOLUME_NAME_DOS;
+  const DWORD length = ::GetFinalPathNameByHandleW(handle, buffer.data(),
+                                                   buffer.size(), name_flags);
+  if (length == 0) {
+    return WindowsStatus("GetFinalPathNameByHandleW", kEllipsis, kEllipsis,
+                         absl::Hex(buffer.size()), absl::Hex(name_flags));
+  }
+  if (length >= buffer.size()) {
+    return absl::FailedPreconditionError(absl::StrFormat(
+        "Resolved filename is too long (%d characters)", length));
+  }
+  return FileName::FromString(std::wstring_view(buffer.data(), length));
+#else
+  char* const absl_nullable result = realpath(this->pointer(), nullptr);
+  if (result == nullptr) return ErrnoStatus("realpath", *this, nullptr);
+  const absl::Cleanup cleanup = [result] { std::free(result); };
+  return FileName::FromString(result);
+#endif
+}
+
 absl::StatusOr<std::string> ReadFile(const FileName& file) {
   std::ifstream stream(file.string(), std::ios::in | std::ios::binary);
   if (!stream.is_open() || !stream.good()) {

elisp/private/tools/system.h

@@ -92,6 +92,7 @@ class FileName final {
 
   bool IsAbsolute() const;
   absl::StatusOr<FileName> MakeAbsolute() const;
+  absl::StatusOr<FileName> Resolve() const;
   absl::StatusOr<FileName> MakeRelative(const FileName& base) const;
 
   friend bool operator==(const FileName& a, const FileName& b) {

tests/tools/system_test.cc

@@ -449,6 +449,36 @@ TEST(MakeRelativeTest, Relativizes) {
   }
 }
 
+TEST(FileNameTest, ResolveRejectsNonExisting) {
+  const absl::StatusOr<FileName> dir = TempDir();
+  ASSERT_THAT(dir, IsOk());
+
+  const FileName file =
+      dir->Child(RULES_ELISP_NATIVE_LITERAL("nonexisting")).value();
+
+  EXPECT_THAT(file.Resolve(), StatusIs(absl::StatusCode::kNotFound));
+}
+
+TEST(FileNameTest, ResolvesRegularFile) {
+  const absl::StatusOr<FileName> dir = TempDir();
+  ASSERT_THAT(dir, IsOk());
+
+  const FileName file = dir->Child(RULES_ELISP_NATIVE_LITERAL("file")).value();
+  EXPECT_THAT(WriteFile(file, "contents"), IsOk());
+  const absl::Cleanup cleanup = [&file] { EXPECT_THAT(Unlink(file), IsOk()); };
+
+  const absl::StatusOr<FileName> resolved = file.Resolve();
+  ASSERT_THAT(resolved, IsOk());
+  EXPECT_THAT(ReadFile(*resolved), IsOkAndHolds("contents"));
+}
+
+TEST(FileNameTest, ResolvesDirectory) {
+  const absl::StatusOr<FileName> dir = TempDir();
+  ASSERT_THAT(dir, IsOk());
+
+  EXPECT_THAT(dir->Resolve(), IsOk());
+}
+
 TEST(FileExistsTest, TestsThatFileExists) {
   const absl::StatusOr<FileName> dir = TempDir();
   ASSERT_THAT(dir, IsOk());