Return AutoCloseFD in open-like functions

This reflects the fact that it is returning a new, "owned" file
descriptor, that it is the caller's responsibility to close.

Co-authored-by: Amaan Qureshi <git@amaanq.com>

src/libexpr/eval-profiler.cc

@@ -137,7 +137,7 @@ public:
         : state(state)
         , sampleInterval(period)
         , profileFd([&]() {
-            AutoCloseFD fd = openNewFileForWrite(
+            auto fd = openNewFileForWrite(
                 profileFile,
                 0660,
                 {

src/libstore/gc.cc

@@ -554,7 +554,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
            by another process. We need to be sure that we can acquire an
            exclusive lock before deleting them. */
         if (baseName.find("tmp-", 0) == 0) {
-            AutoCloseFD tmpDirFd = openDirectory(realPath);
+            auto tmpDirFd = openDirectory(realPath);
             if (!tmpDirFd || !lockFile(tmpDirFd.get(), ltWrite, false)) {
                 debug("skipping locked tempdir %s", PathFmt(realPath));
                 return;

src/libutil-tests/file-system-at.cc

@@ -45,7 +45,7 @@ TEST(readLinkAt, works)
         sink.createDirectory(CanonPath("dir"));
     }
 
-    AutoCloseFD dirFd = openDirectory(tmpDir);
+    auto dirFd = openDirectory(tmpDir);
 
     EXPECT_EQ(readLinkAt(dirFd.get(), CanonPath("link")), OS_STR("target"));
     EXPECT_EQ(readLinkAt(dirFd.get(), CanonPath("relative")), OS_STR("../relative/path"));
@@ -54,7 +54,7 @@ TEST(readLinkAt, works)
     EXPECT_EQ(readLinkAt(dirFd.get(), CanonPath("long")), string_to_os_string(longTarget));
     EXPECT_EQ(readLinkAt(dirFd.get(), CanonPath("a/b/link")), OS_STR("nested_target"));
 
-    AutoCloseFD subDirFd = openDirectory(tmpDir / "a");
+    auto subDirFd = openDirectory(tmpDir / "a");
     EXPECT_EQ(readLinkAt(subDirFd.get(), CanonPath("b/link")), OS_STR("nested_target"));
 
     // Test error cases - expect SystemError on both platforms
@@ -107,7 +107,7 @@ TEST(openFileEnsureBeneathNoSymlinks, works)
             SymlinkNotAllowed);
     }
 
-    AutoCloseFD dirFd = openDirectory(tmpDir);
+    auto dirFd = openDirectory(tmpDir);
 
     // Helper to open files with platform-specific arguments
     auto openRead = [&](std::string_view path) -> AutoCloseFD {

src/libutil-tests/unix/file-system-at.cc

@@ -39,7 +39,7 @@ TEST(fchmodatTryNoFollow, works)
     ASSERT_NO_THROW(chmod(tmpDir / "file", 0644));
     ASSERT_NO_THROW(chmod(tmpDir / "dir", 0755));
 
-    AutoCloseFD dirFd = openDirectory(tmpDir);
+    auto dirFd = openDirectory(tmpDir);
     ASSERT_TRUE(dirFd);
 
     struct ::stat st;
@@ -104,7 +104,7 @@ TEST(fchmodatTryNoFollow, fallbackWithoutProc)
             if (mount("tmpfs", "/proc", "tmpfs", 0, 0) == -1)
                 _exit(1);
 
-            AutoCloseFD dirFd = openDirectory(tmpDir);
+            auto dirFd = openDirectory(tmpDir);
             if (!dirFd)
                 exit(1);
 

src/libutil/file-system.cc

@@ -263,7 +263,7 @@ std::filesystem::path readLink(const std::filesystem::path & path)
 
 std::string readFile(const std::filesystem::path & path)
 {
-    AutoCloseFD fd = openFileReadonly(path);
+    auto fd = openFileReadonly(path);
     if (!fd)
         throw NativeSysError("opening file %1%", PathFmt(path));
     return readFile(fd.get());
@@ -286,7 +286,7 @@ void readFile(const std::filesystem::path & path, Sink & sink, bool memory_map)
     }
 
     // Stream the file instead if memory-mapping fails or is disabled.
-    AutoCloseFD fd = openFileReadonly(std::filesystem::path(path));
+    auto fd = openFileReadonly(std::filesystem::path(path));
     if (!fd)
         throw NativeSysError("opening file %s", PathFmt(path));
     drainFD(fd.get(), sink);

src/libutil/include/nix/util/file-system.hh

@@ -168,14 +168,14 @@ std::filesystem::path descriptorToPath(Descriptor fd);
 /**
  * Open a `Descriptor` with read-only access to the given directory.
  */
-Descriptor openDirectory(const std::filesystem::path & path);
+AutoCloseFD openDirectory(const std::filesystem::path & path);
 
 /**
  * Open a `Descriptor` with read-only access to the given file.
  *
  * @note For directories use @ref openDirectory.
  */
-Descriptor openFileReadonly(const std::filesystem::path & path);
+AutoCloseFD openFileReadonly(const std::filesystem::path & path);
 
 struct OpenNewFileForWriteParams
 {
@@ -198,7 +198,7 @@ struct OpenNewFileForWriteParams
  *
  * @todo Reparse points on Windows.
  */
-Descriptor openNewFileForWrite(const std::filesystem::path & path, mode_t mode, OpenNewFileForWriteParams params);
+AutoCloseFD openNewFileForWrite(const std::filesystem::path & path, mode_t mode, OpenNewFileForWriteParams params);
 
 /**
  * Read the contents of a file into a string.

src/libutil/nar-accessor.cc

@@ -153,7 +153,7 @@ ref<NarAccessor> makeLazyNarAccessor(NarListing listing, GetNarBytes getNarBytes
 
 GetNarBytes seekableGetNarBytes(const std::filesystem::path & path)
 {
-    AutoCloseFD fd = openFileReadonly(path);
+    auto fd = openFileReadonly(path);
     if (!fd)
         throw NativeSysError("opening NAR cache file %s", PathFmt(path));
 

src/libutil/unix/file-system.cc

@@ -23,17 +23,17 @@
 
 namespace nix {
 
-Descriptor openDirectory(const std::filesystem::path & path)
+AutoCloseFD openDirectory(const std::filesystem::path & path)
 {
-    return open(path.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+    return AutoCloseFD{open(path.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC)};
 }
 
-Descriptor openFileReadonly(const std::filesystem::path & path)
+AutoCloseFD openFileReadonly(const std::filesystem::path & path)
 {
-    return open(path.c_str(), O_RDONLY | O_CLOEXEC);
+    return AutoCloseFD{open(path.c_str(), O_RDONLY | O_CLOEXEC)};
 }
 
-Descriptor openNewFileForWrite(const std::filesystem::path & path, mode_t mode, OpenNewFileForWriteParams params)
+AutoCloseFD openNewFileForWrite(const std::filesystem::path & path, mode_t mode, OpenNewFileForWriteParams params)
 {
     auto flags = O_WRONLY | O_CREAT | O_CLOEXEC;
     if (params.truncateExisting) {
@@ -43,7 +43,7 @@ Descriptor openNewFileForWrite(const std::filesystem::path & path, mode_t mode,
     } else {
         flags |= O_EXCL; /* O_CREAT | O_EXCL already ensures that symlinks are not followed. */
     }
-    return open(path.c_str(), flags, mode);
+    return AutoCloseFD{open(path.c_str(), flags, mode)};
 }
 
 std::filesystem::path descriptorToPath(Descriptor fd)

src/libutil/windows/file-system.cc

@@ -23,41 +23,41 @@ void setWriteTime(
     warn("Changing file times is not yet implemented on Windows, path is %s", PathFmt(path));
 }
 
-Descriptor openDirectory(const std::filesystem::path & path)
+AutoCloseFD openDirectory(const std::filesystem::path & path)
 {
-    return CreateFileW(
+    return AutoCloseFD{CreateFileW(
         path.c_str(),
         GENERIC_READ,
         FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
         /*lpSecurityAttributes=*/nullptr,
         OPEN_EXISTING,
         FILE_FLAG_BACKUP_SEMANTICS,
-        /*hTemplateFile=*/nullptr);
+        /*hTemplateFile=*/nullptr)};
 }
 
-Descriptor openFileReadonly(const std::filesystem::path & path)
+AutoCloseFD openFileReadonly(const std::filesystem::path & path)
 {
-    return CreateFileW(
+    return AutoCloseFD{CreateFileW(
         path.c_str(),
         GENERIC_READ,
         FILE_SHARE_READ | FILE_SHARE_DELETE,
         /*lpSecurityAttributes=*/nullptr,
         OPEN_EXISTING,
         FILE_ATTRIBUTE_NORMAL,
-        /*hTemplateFile=*/nullptr);
+        /*hTemplateFile=*/nullptr)};
 }
 
-Descriptor
+AutoCloseFD
 openNewFileForWrite(const std::filesystem::path & path, [[maybe_unused]] mode_t mode, OpenNewFileForWriteParams params)
 {
-    return CreateFileW(
+    return AutoCloseFD{CreateFileW(
         path.c_str(),
         GENERIC_WRITE,
         FILE_SHARE_READ | FILE_SHARE_DELETE,
         /*lpSecurityAttributes=*/nullptr,
         params.truncateExisting ? CREATE_ALWAYS : CREATE_NEW, /* TODO: Reparse points. */
         FILE_ATTRIBUTE_NORMAL,
-        /*hTemplateFile=*/nullptr);
+        /*hTemplateFile=*/nullptr)};
 }
 
 std::filesystem::path defaultTempDir()

src/nix/cat.cc

@@ -78,7 +78,7 @@ struct CmdCatNar : StoreCommand, MixCat
 
     void run(ref<Store> store) override
     {
-        AutoCloseFD fd = openFileReadonly(narPath);
+        auto fd = openFileReadonly(narPath);
         if (!fd)
             throw NativeSysError("opening NAR file %s", PathFmt(narPath));
         auto source = FdSource{fd.get()};

src/nix/ls.cc

@@ -150,7 +150,7 @@ struct CmdLsNar : Command, MixLs
 
     void run() override
     {
-        AutoCloseFD fd = openFileReadonly(narPath);
+        auto fd = openFileReadonly(narPath);
         if (!fd)
             throw NativeSysError("opening NAR file %s", PathFmt(narPath));
         auto source = FdSource{fd.get()};

src/nix/nix-channel/nix-channel.cc

@@ -45,7 +45,7 @@ static void readChannels()
 // Writes the list of channels.
 static void writeChannels()
 {
-    AutoCloseFD channelsFD = openNewFileForWrite(
+    auto channelsFD = openNewFileForWrite(
         channelsList,
         0644,
         {

src/nix/prefetch.cc

@@ -112,7 +112,7 @@ std::tuple<StorePath, Hash> prefetchFile(
             if (executable)
                 mode = 0700;
 
-            AutoCloseFD fd = openNewFileForWrite(tmpFile, mode, {.truncateExisting = false});
+            auto fd = openNewFileForWrite(tmpFile, mode, {.truncateExisting = false});
             if (!fd)
                 throw SysError("creating temporary file %s", PathFmt(tmpFile));