Get rid of SysError and WinError derived classes

All we need is `SystemError`, and the various ways to construct it can
be done with static methods that are more informative. Catching the
derived classes was a footgun that is now impossible, because one can
only has `SystemError` to catch.

I did however make `SysError` and `WinError` top-level function
wrappers in order to avoid churn in the vast majority of call sites.

src/libstore/local-fs-store.cc

@@ -1,6 +1,5 @@
 #include "nix/util/archive.hh"
 #include "nix/util/posix-source-accessor.hh"
-#include "nix/util/posix-source-accessor.hh"
 #include "nix/store/store-api.hh"
 #include "nix/store/local-fs-store.hh"
 #include "nix/store/globals.hh"
@@ -110,7 +109,7 @@ std::shared_ptr<SourceAccessor> LocalFSStore::getFSAccessor(const StorePath & pa
         if (!pathExists(absPath))
             return nullptr;
     }
-    return makeFSSourceAccessor(std::move(absPath));
+    return std::make_shared<PosixSourceAccessor>(std::move(absPath));
 }
 
 const std::string LocalFSStore::drvsLogDir = "drvs";

src/libstore/posix-fs-canonicalise.cc

@@ -5,7 +5,6 @@
 #include "nix/util/util.hh"
 #include "nix/store/store-api.hh"
 #include "nix/store/globals.hh"
-#include "nix/util/file-system-at.hh"
 #include "store-config-private.hh"
 
 #if NIX_SUPPORT_ACL

src/libstore/unix/build/derivation-builder.cc

@@ -758,7 +758,7 @@ std::optional<Descriptor> DerivationBuilderImpl::startBuild()
 
     /* The TOCTOU between the previous mkdir call and this open call is unavoidable due to
        POSIX semantics.*/
-    tmpDirFd = openDirectory(tmpDir, /*followFinalSymlink=*/false);
+    tmpDirFd = AutoCloseFD{open(tmpDir.c_str(), O_RDONLY | O_NOFOLLOW | O_DIRECTORY)};
     if (!tmpDirFd)
         throw SysError("failed to open the build temporary directory descriptor %1%", PathFmt(tmpDir));
 
@@ -1269,7 +1269,7 @@ void DerivationBuilderImpl::writeBuilderFile(const std::string & name, std::stri
         openat(tmpDirFd.get(), name.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC | O_EXCL | O_NOFOLLOW, 0666)};
     if (!fd)
         throw SysError("creating file %s", PathFmt(path));
-    writeFile(fd.get(), contents);
+    writeFile(fd, path, contents);
     chownToBuilder(fd.get(), path);
 }
 

src/libstore/unix/pathlocks.cc

@@ -1,5 +1,5 @@
 #include "nix/store/pathlocks.hh"
-#include "nix/util/file-system-at.hh"
+#include "nix/util/file-system.hh"
 #include "nix/util/util.hh"
 #include "nix/util/sync.hh"
 #include "nix/util/signals.hh"

src/libstore/windows/pathlocks.cc

@@ -56,26 +56,24 @@ bool lockFile(Descriptor desc, LockType lockType, bool wait)
     switch (lockType) {
     case ltNone: {
         OVERLAPPED ov = {0};
-        if (!UnlockFileEx(desc, 0, 2, 0, &ov)) {
-            WinError winError("Failed to unlock file desc %s", desc);
-            throw winError;
-        }
+        if (!UnlockFileEx(desc, 0, 2, 0, &ov))
+            throw WinError("Failed to unlock file desc %s", desc);
         return true;
     }
     case ltRead: {
         OVERLAPPED ov = {0};
         if (!LockFileEx(desc, wait ? 0 : LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &ov)) {
-            WinError winError("Failed to lock file desc %s", desc);
-            if (winError.lastError == ERROR_LOCK_VIOLATION)
+            auto lastError = GetLastError();
+            if (lastError == ERROR_LOCK_VIOLATION)
                 return false;
-            throw winError;
+            throw WinError(lastError, "Failed to lock file desc %s", desc);
         }
 
         ov.Offset = 1;
         if (!UnlockFileEx(desc, 0, 1, 0, &ov)) {
-            WinError winError("Failed to unlock file desc %s", desc);
-            if (winError.lastError != ERROR_NOT_LOCKED)
-                throw winError;
+            auto lastError = GetLastError();
+            if (lastError != ERROR_NOT_LOCKED)
+                throw WinError(lastError, "Failed to unlock file desc %s", desc);
         }
         return true;
     }
@@ -83,17 +81,17 @@ bool lockFile(Descriptor desc, LockType lockType, bool wait)
         OVERLAPPED ov = {0};
         ov.Offset = 1;
         if (!LockFileEx(desc, LOCKFILE_EXCLUSIVE_LOCK | (wait ? 0 : LOCKFILE_FAIL_IMMEDIATELY), 0, 1, 0, &ov)) {
-            WinError winError("Failed to lock file desc %s", desc);
-            if (winError.lastError == ERROR_LOCK_VIOLATION)
+            auto lastError = GetLastError();
+            if (lastError == ERROR_LOCK_VIOLATION)
                 return false;
-            throw winError;
+            throw WinError(lastError, "Failed to lock file desc %s", desc);
         }
 
         ov.Offset = 0;
         if (!UnlockFileEx(desc, 0, 1, 0, &ov)) {
-            WinError winError("Failed to unlock file desc %s", desc);
-            if (winError.lastError != ERROR_NOT_LOCKED)
-                throw winError;
+            auto lastError = GetLastError();
+            if (lastError != ERROR_NOT_LOCKED)
+                throw WinError(lastError, "Failed to unlock file desc %s", desc);
         }
         return true;
     }

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

@@ -1,11 +1,10 @@
 #include <gtest/gtest.h>
+#include <gmock/gmock.h>
 
 #include "nix/util/file-system-at.hh"
 #include "nix/util/file-system.hh"
 #include "nix/util/fs-sink.hh"
 
-#include <cstring>
-
 namespace nix {
 
 /* ----------------------------------------------------------------------------

src/libutil-tests/source-accessor.cc

@@ -91,7 +91,9 @@ TEST_F(FSSourceAccessorTest, works)
     {
         RestoreSink sink(false);
         sink.dstPath = tmpDir;
+#ifndef _WIN32
         sink.dirFd = openDirectory(tmpDir);
+#endif
         sink.createDirectory(CanonPath("subdir"));
         sink.createRegularFile(CanonPath("file1"), [](CreateRegularFileSink & crf) { crf("content1"); });
         sink.createRegularFile(CanonPath("subdir/file2"), [](CreateRegularFileSink & crf) { crf("content2"); });
@@ -135,34 +137,4 @@ TEST_F(FSSourceAccessorTest, works)
     }
 }
 
-/* ----------------------------------------------------------------------------
- * RestoreSink non-directory at root (no dirFd)
- * --------------------------------------------------------------------------*/
-
-TEST_F(FSSourceAccessorTest, RestoreSinkRegularFileAtRoot)
-{
-    auto filePath = tmpDir / "rootfile";
-    {
-        RestoreSink sink(false);
-        sink.dstPath = filePath;
-        // No dirFd set - this tests the !dirFd path
-        sink.createRegularFile(CanonPath::root, [](CreateRegularFileSink & crf) { crf("root content"); });
-    }
-
-    EXPECT_THAT(makeFSSourceAccessor(filePath), HasContents(CanonPath::root, "root content"));
-}
-
-TEST_F(FSSourceAccessorTest, RestoreSinkSymlinkAtRoot)
-{
-    auto linkPath = tmpDir / "rootlink";
-    {
-        RestoreSink sink(false);
-        sink.dstPath = linkPath;
-        // No dirFd set - this tests the !dirFd path
-        sink.createSymlink(CanonPath::root, "symlink_target");
-    }
-
-    EXPECT_THAT(makeFSSourceAccessor(linkPath), HasSymlink(CanonPath::root, "symlink_target"));
-}
-
 } // namespace nix

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

@@ -47,16 +47,16 @@ TEST(fchmodatTryNoFollow, works)
     /* Check that symlinks are not followed and targets are not changed. */
 
     EXPECT_NO_THROW(
-        try { fchmodatTryNoFollow(dirFd.get(), CanonPath("filelink"), 0777); } catch (SysError & e) {
-            if (e.errNo != EOPNOTSUPP)
+        try { fchmodatTryNoFollow(dirFd.get(), CanonPath("filelink"), 0777); } catch (SystemError & e) {
+            if (!e.is(std::errc::operation_not_supported))
                 throw;
         });
     ASSERT_EQ(stat((tmpDir / "file").c_str(), &st), 0);
     EXPECT_EQ(st.st_mode & 0777, 0644);
 
     EXPECT_NO_THROW(
-        try { fchmodatTryNoFollow(dirFd.get(), CanonPath("dirlink"), 0777); } catch (SysError & e) {
-            if (e.errNo != EOPNOTSUPP)
+        try { fchmodatTryNoFollow(dirFd.get(), CanonPath("dirlink"), 0777); } catch (SystemError & e) {
+            if (!e.is(std::errc::operation_not_supported))
                 throw;
         });
     ASSERT_EQ(stat((tmpDir / "dir").c_str(), &st), 0);
@@ -110,14 +110,14 @@ TEST(fchmodatTryNoFollow, fallbackWithoutProc)
 
             try {
                 fchmodatTryNoFollow(dirFd.get(), CanonPath("file"), 0600);
-            } catch (SysError & e) {
+            } catch (SystemError & e) {
                 _exit(1);
             }
 
             try {
                 fchmodatTryNoFollow(dirFd.get(), CanonPath("link"), 0777);
-            } catch (SysError & e) {
-                if (e.errNo == EOPNOTSUPP)
+            } catch (SystemError & e) {
+                if (e.is(std::errc::operation_not_supported))
                     _exit(0); /* Success. */
             }
 

src/libutil/directory-source-accessor.cc

@@ -1,285 +0,0 @@
-// FIXME: detect in meson
-#define HAVE_OPENAT2 1
-#define HAVE_OPENAT 1
-
-#include "util-config-private.hh"
-#include "nix/util/signals.hh"
-#include "nix/util/directory-source-accessor.hh"
-#include "nix/util/posix-source-accessor.hh"
-
-#if defined(__linux__) && HAVE_OPENAT2
-#  include <sys/syscall.h>
-#  include <linux/openat2.h>
-#endif
-
-#include <atomic>
-#include <ranges>
-
-namespace nix {
-
-#if HAVE_OPENAT
-
-namespace {
-
-class DirFdSourceAccessor : public SourceAccessor
-{
-    /**
-     * File descriptor of the root directory.
-     */
-    AutoCloseFD dirFd;
-
-    /**
-     * Path corresponding to the accessor.
-     * @warning Do not use for any file operations!
-     */
-    std::filesystem::path root;
-
-    /**
-     * The most recent mtime seen by lstat(). This is a hack to
-     * support dumpPathAndGetMtime(). Should remove this eventually.
-     */
-    time_t mtime = 0;
-
-    bool trackLastModified = false;
-
-    AutoCloseFD openFile(const CanonPath & path, int flags)
-    {
-        if (path.isRoot())
-            return ::openat(dirFd.get(), ".", flags);
-
-#  if defined(__linux__) && HAVE_OPENAT2
-        /* Cache the result of whether openat2 is not supported. */
-        static std::atomic_flag openat2Unsupported = ATOMIC_FLAG_INIT;
-
-        if (!openat2Unsupported.test()) {
-            /* No glibc wrapper yet, but there's a patch:
-             * https://patchwork.sourceware.org/project/glibc/patch/20251029200519.3203914-1-adhemerval.zanella@linaro.org/
-             */
-            auto how = ::open_how{
-                .flags = static_cast<decltype(::open_how::flags)>(flags),
-                /* Symlinks are disallowed. RESOLVE_BENEATH is a bit overkill, since
-                   CanonPath has the invariant of not having any `..` components, but
-                   that's good practice anyway. */
-                .resolve = RESOLVE_NO_SYMLINKS | RESOLVE_BENEATH,
-            };
-
-            auto res = ::syscall(__NR_openat2, dirFd.get(), path.rel_c_str(), &how, sizeof(how));
-            if (res < 0 && errno == ENOSYS) {
-                /* Cache that the syscall is not supported and fall through to openat. */
-                openat2Unsupported.test_and_set();
-            } else {
-                return res;
-            }
-        }
-#  endif
-
-        AutoCloseFD parentFd;
-        auto nrComponents = std::ranges::distance(path);
-        auto components = std::views::take(path, nrComponents - 1); /* Everything but last component */
-        auto getParentFd = [&]() { return parentFd ? parentFd.get() : dirFd.get(); };
-
-        /* This rather convoluted loop is necessary to avoid TOCTOU when validating that
-           no inner path component is a symlink. */
-        for (auto it = components.begin(); it != components.end(); ++it) {
-            std::string_view component = *it;
-            parentFd = ::openat(
-                getParentFd(),                  /* First iteration uses dirFd. */
-                std::string(component).c_str(), /* Copy into a string to make NUL terminated. */
-                O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC |
-#  ifdef __linux__
-                    O_PATH /* Linux-specific optimization. Files are open only for path resolution purposes. */
-#  endif
-            );
-
-            if (!parentFd) {
-                /* Construct the CanonPath for error message. */
-                auto path2 = std::ranges::fold_left(components.begin(), ++it, CanonPath::root, [](auto lhs, auto rhs) {
-                    lhs.push(rhs);
-                    return lhs;
-                });
-
-                if (errno == ELOOP)
-                    /* Do not allow any simlinks in internal path components.
-                       This is what is necessary to emulate it without RESOLVE_NO_SYMLINKS. */
-                    throw Error("path '%s' is a symlink", showPath(path2));
-
-                return AutoCloseFD();
-            }
-        }
-
-        return ::openat(getParentFd(), std::string(path.baseName().value()).c_str(), flags);
-    }
-
-    std::optional<struct ::stat> maybeLstatImpl(const CanonPath & path)
-    {
-        std::optional<struct ::stat> st{std::in_place};
-
-        if (path.isRoot()) {
-            if (::fstat(dirFd.get(), &*st)) /* Is already open. */
-                throw SysError("getting status of '%s'", showPath(path));
-            return st;
-        }
-
-        auto parentPath = path.parent().value();
-        auto fd = openFile(parentPath, O_PATH | O_NOFOLLOW | O_CLOEXEC | O_DIRECTORY);
-        if (!fd) {
-            if (errno == ENOENT || errno == ENOTDIR)
-                return std::nullopt;
-            throw SysError("opening parent path of '%s'", showPath(path));
-        }
-
-        /* Should have the same semantics as lstat on a path. */
-        if (::fstatat(fd.get(), std::string(path.baseName().value()).c_str(), &*st, AT_SYMLINK_NOFOLLOW)) {
-            if (errno == ENOENT || errno == ENOTDIR)
-                st.reset();
-            else
-                throw SysError("getting status of '%s'", showPath(path));
-        }
-
-        /* The contract is that trackLastModified implies that the caller uses the accessor
-           from a single thread. Thus this is not a CAS loop. */
-        if (trackLastModified)
-            mtime = std::max(mtime, st->st_mtime);
-
-        return st;
-    }
-
-public:
-    DirFdSourceAccessor(AutoCloseFD rootFd_, std::filesystem::path root_, bool trackLastModified)
-        : dirFd(std::move(rootFd_))
-        , root(std::move(root_))
-        , trackLastModified(trackLastModified)
-    {
-        if (root != root.root_path()) /* Don't prefix root directory. */
-            displayPrefix = root.string();
-    }
-
-    void readFile(const CanonPath & path, Sink & sink, std::function<void(uint64_t)> sizeCallback) override
-    {
-        auto fd = openFile(path, O_RDONLY | O_NOFOLLOW | O_CLOEXEC);
-
-        auto size = getFileSize(fd.get());
-        sizeCallback(size);
-        drainFD(fd.get(), sink, {.expectedSize = size});
-    }
-
-    bool pathExists(const CanonPath & path) override
-    {
-        return maybeLstatImpl(path).has_value();
-    }
-
-    std::optional<Stat> maybeLstat(const CanonPath & path) override
-    {
-        // TODO: Deduplicate with PosixSourceAccessor.
-
-        auto st = maybeLstatImpl(path);
-        if (!st)
-            return std::nullopt;
-
-        /* The contract is that trackLastModified implies that the caller uses the accessor
-           from a single thread. Thus this is not a CAS loop. */
-        if (trackLastModified)
-            mtime = std::max(mtime, st->st_mtime);
-
-        return PosixSourceAccessor::makeStat(*st);
-    }
-
-    DirEntries readDirectory(const CanonPath & path) override
-    {
-        auto fd = openFile(path, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-        if (!fd)
-            throw SysError("opening directory '%1%'", path);
-
-        auto dir = AutoCloseDir{::fdopendir(fd.get())};
-        if (!dir)
-            throw SysError("opening directory '%1%'", path);
-
-        fd.release();
-
-        DirEntries entries;
-        struct dirent * dirent;
-
-        while (errno = 0, dirent = ::readdir(dir.get())) {
-            checkInterrupt();
-            std::string name = dirent->d_name;
-            if (name == "." || name == "..")
-                continue;
-
-            auto type = [&]() -> std::optional<Type> {
-                switch (dirent->d_type) {
-                case DT_REG:
-                    return tRegular;
-                case DT_DIR:
-                    return tDirectory;
-                case DT_LNK:
-                    return tSymlink;
-                case DT_BLK:
-                    return tBlock;
-                case DT_CHR:
-                    return tChar;
-                case DT_FIFO:
-                    return tFifo;
-                case DT_SOCK:
-                    return tSocket;
-                case DT_UNKNOWN:
-                default:
-                    return std::nullopt;
-                }
-            }();
-
-            entries.emplace(std::move(name), type);
-        }
-
-        if (errno)
-            throw SysError("reading directory '%1%'", showPath(path));
-
-        return entries;
-    }
-
-    std::string readLink(const CanonPath & path) override
-    {
-        if (path.isRoot())
-            throw Error("file '%s' is not a symbolic link", path);
-
-        auto parentPath = path.parent().value();
-        auto basename = std::string(path.baseName().value());
-
-        auto parentFd = openFile(
-            parentPath,
-            O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC |
-#  ifdef __linux__
-                O_PATH
-#  endif
-        );
-        if (!parentFd)
-            throw SysError("opening path '%1%'", showPath(parentPath));
-
-        std::string target;
-        target.resize(PATH_MAX);
-        auto len = ::readlinkat(parentFd.get(), basename.c_str(), target.data(), target.size());
-        if (len < 0)
-            throw SysError("reading link '%1%'", showPath(path));
-        target.resize(len);
-        return target;
-    }
-
-    std::optional<std::filesystem::path> getPhysicalPath(const CanonPath & path) override
-    {
-        return root / path.rel();
-    }
-};
-
-} // namespace
-
-#endif
-
-ref<SourceAccessor> makeDirectorySourceAccessor(AutoCloseFD fd, std::filesystem::path root, bool trackLastModified)
-{
-#if HAVE_OPENAT
-    return make_ref<DirFdSourceAccessor>(std::move(fd), std::move(root), trackLastModified);
-#else
-    return make_ref<PosixSourceAccessor>(std::move(root), trackLastModified);
-#endif
-}
-
-} // namespace nix

src/libutil/file-descriptor.cc

@@ -184,6 +184,24 @@ void AutoCloseFD::close()
     }
 }
 
+void AutoCloseFD::fsync() const
+{
+    if (fd != INVALID_DESCRIPTOR) {
+        int result;
+        result =
+#ifdef _WIN32
+            ::FlushFileBuffers(fd)
+#elif defined(__APPLE__)
+            ::fcntl(fd, F_FULLFSYNC)
+#else
+            ::fsync(fd)
+#endif
+            ;
+        if (result == -1)
+            throw NativeSysError("fsync file descriptor %1%", fd);
+    }
+}
+
 void AutoCloseFD::startFsync() const
 {
 #ifdef __linux__

src/libutil/file-system-at.cc

@@ -1,16 +0,0 @@
-#include "nix/util/file-system-at.hh"
-
-namespace nix {
-
-std::optional<PosixStat> maybeFstatat(Descriptor dirFd, const CanonPath & path)
-{
-    try {
-        return fstatat(dirFd, path);
-    } catch (SystemError & e) {
-        if (e.is(std::errc::no_such_file_or_directory) || e.is(std::errc::not_a_directory))
-            return std::nullopt;
-        throw;
-    }
-}
-
-} // namespace nix

src/libutil/file-system.cc

@@ -195,42 +195,71 @@ bool isDirOrInDir(const std::filesystem::path & path, const std::filesystem::pat
     return path == dir || isInDir(path, dir);
 }
 
+#ifdef _WIN32
+#  define STAT _wstat64
+#  define LSTAT _wstat64
+#else
+#  define STAT stat
+#  define LSTAT lstat
+#endif
+
 PosixStat stat(const std::filesystem::path & path)
+{
+    PosixStat st;
+    if (STAT(path.c_str(), &st))
+        throw SysError("getting status of %s", PathFmt(path));
+    return st;
+}
+
+PosixStat lstat(const std::filesystem::path & path)
+{
+    PosixStat st;
+    if (LSTAT(path.c_str(), &st))
+        throw SysError("getting status of %s", PathFmt(path));
+    return st;
+}
+
+PosixStat fstat(int fd)
 {
     PosixStat st;
     if (
 #ifdef _WIN32
-        _wstat64
+        _fstat64
 #else
-        ::stat
+        ::fstat
 #endif
-        (path.c_str(), &st))
-        throw SysError("getting status of %s", PathFmt(path));
+        (fd, &st))
+        throw SysError("getting status of fd %d", fd);
     return st;
 }
 
 std::optional<PosixStat> maybeStat(const std::filesystem::path & path)
 {
-    try {
-        return stat(path);
-    } catch (SystemError & e) {
-        if (e.is(std::errc::no_such_file_or_directory) || e.is(std::errc::not_a_directory))
-            return std::nullopt;
-        throw;
+    std::optional<PosixStat> st{std::in_place};
+    if (STAT(path.c_str(), &*st)) {
+        if (errno == ENOENT || errno == ENOTDIR)
+            st.reset();
+        else
+            throw SysError("getting status of %s", PathFmt(path));
     }
+    return st;
 }
 
 std::optional<PosixStat> maybeLstat(const std::filesystem::path & path)
 {
-    try {
-        return lstat(path);
-    } catch (SystemError & e) {
-        if (e.is(std::errc::no_such_file_or_directory) || e.is(std::errc::not_a_directory))
-            return std::nullopt;
-        throw;
+    std::optional<PosixStat> st{std::in_place};
+    if (LSTAT(path.c_str(), &*st)) {
+        if (errno == ENOENT || errno == ENOTDIR)
+            st.reset();
+        else
+            throw SysError("getting status of %s", PathFmt(path));
     }
+    return st;
 }
 
+#undef STAT
+#undef LSTAT
+
 bool pathExists(const std::filesystem::path & path)
 {
     return maybeLstat(path.string()).has_value();
@@ -311,23 +340,23 @@ void writeFile(const Path & path, std::string_view s, mode_t mode, FsSync sync)
     if (!fd)
         throw SysError("opening file '%1%'", path);
 
-    writeFile(fd.get(), s, sync, &path);
+    writeFile(fd, path, s, mode, sync);
 
     /* Close explicitly to propagate the exceptions. */
     fd.close();
 }
 
-void writeFile(Descriptor fd, std::string_view s, FsSync sync, const Path * origPath)
+void writeFile(AutoCloseFD & fd, const Path & origPath, std::string_view s, mode_t mode, FsSync sync)
 {
-    assert(fd != INVALID_DESCRIPTOR);
+    assert(fd);
     try {
-        writeFull(fd, s);
+        writeFull(fd.get(), s);
 
         if (sync == FsSync::Yes)
-            syncDescriptor(fd);
+            fd.fsync();
 
     } catch (Error & e) {
-        e.addTrace({}, "writing file '%1%'", origPath ? *origPath : descriptorToPath(fd).string());
+        e.addTrace({}, "writing file '%1%'", origPath);
         throw;
     }
 }

src/libutil/fs-sink.cc

@@ -105,26 +105,34 @@ void RestoreSink::createDirectory(const CanonPath & path)
 {
     auto p = append(dstPath, path);
 
+#ifndef _WIN32
     if (dirFd) {
         if (path.isRoot())
             /* Trying to create a directory that we already have a file descriptor for. */
             throw Error("path %s already exists", PathFmt(p));
 
-        createDirectoryAt(dirFd.get(), path);
+        if (::mkdirat(dirFd.get(), path.rel_c_str(), 0777) == -1)
+            throw SysError("creating directory %s", PathFmt(p));
+
         return;
     }
+#endif
 
     if (!std::filesystem::create_directory(p))
         throw Error("path '%s' already exists", p.string());
 
+#ifndef _WIN32
     if (path.isRoot()) {
         assert(!dirFd); // Handled above
 
         /* Open directory for further *at operations relative to the sink root
            directory. */
-        dirFd = openDirectory(p, /*followFinalSymlink=*/false);
+        dirFd = open(p.c_str(), O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+        if (!dirFd)
+            throw SysError("creating directory %1%", PathFmt(p));
     }
-}
+#endif
+};
 
 struct RestoreRegularFile : CreateRegularFileSink, FdSink
 {
@@ -156,26 +164,28 @@ void RestoreSink::createRegularFile(const CanonPath & path, std::function<void(C
 {
     auto p = append(dstPath, path);
 
-    auto crf = RestoreRegularFile(startFsync, [&]() -> Descriptor {
-        AutoCloseFD parentFd;
-        if (!dirFd) {
-            assert(path.isRoot());
-            assert(p.has_parent_path());
-            parentFd = openDirectory(p.parent_path());
-        }
-        return openFileEnsureBeneathNoSymlinks(
-            dirFd ? dirFd.get() : parentFd.get(),
-            dirFd ? path : CanonPath::root / p.filename().string(),
+    auto crf = RestoreRegularFile(
+        startFsync,
 #ifdef _WIN32
+        CreateFileW(
+            p.c_str(),
             GENERIC_READ | GENERIC_WRITE,
-            FILE_NON_DIRECTORY_FILE,
-            FILE_CREATE
+            FILE_SHARE_READ | FILE_SHARE_WRITE,
+            NULL,
+            CREATE_NEW,
+            FILE_ATTRIBUTE_NORMAL,
+            NULL)
 #else
-                O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC,
-                0666
+        [&]() {
+            /* O_EXCL together with O_CREAT ensures symbolic links in the last
+               component are not followed. */
+            constexpr int flags = O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC;
+            if (!dirFd)
+                return ::open(p.c_str(), flags, 0666);
+            return openFileEnsureBeneathNoSymlinks(dirFd.get(), path, flags, 0666);
+        }()
 #endif
-        );
-    }());
+    );
     if (!crf.fd)
         throw NativeSysError("creating file %1%", PathFmt(p));
     func(crf);
@@ -214,16 +224,14 @@ void RestoreRegularFile::preallocateContents(uint64_t len)
 void RestoreSink::createSymlink(const CanonPath & path, const std::string & target)
 {
     auto p = append(dstPath, path);
-    AutoCloseFD parentFd;
-    if (!dirFd) {
-        assert(path.isRoot());
-        assert(p.has_parent_path());
-        parentFd = openDirectory(p.parent_path());
+#ifndef _WIN32
+    if (dirFd) {
+        if (::symlinkat(requireCString(target), dirFd.get(), path.rel_c_str()) == -1)
+            throw SysError("creating symlink from %1% -> '%2%'", PathFmt(p), target);
+        return;
     }
-    createUnknownSymlinkAt(
-        dirFd ? dirFd.get() : parentFd.get(),
-        dirFd ? path : CanonPath::root / p.filename().string(),
-        string_to_os_string(target));
+#endif
+    nix::createSymlink(target, p.string());
 }
 
 void RegularFileSink::createRegularFile(const CanonPath & path, std::function<void(CreateRegularFileSink &)> func)

src/libutil/include/nix/util/directory-source-accessor.hh

@@ -1,25 +0,0 @@
-#pragma once
-/// @file
-
-#include "nix/util/source-accessor.hh"
-#include "nix/util/ref.hh"
-
-#include <filesystem>
-
-namespace nix {
-
-/**
- * Create a directory accessor rooted at @param root.
- *
- * On unix accesses are performed with openat. Linux uses openat2 if supported
- * by the kernel (>= 5.6).
- *
- * On Windows returns a PosixSourceAccessor.
- *
- * @param fd Descriptor of the directory.
- * @param root Filesystem path corresponding to fd. Must correspond to a directory.
- */
-ref<SourceAccessor>
-makeDirectorySourceAccessor(AutoCloseFD fd, std::filesystem::path root, bool trackLastModified = false);
-
-} // namespace nix

src/libutil/include/nix/util/error.hh

@@ -250,18 +250,15 @@ class SystemError : public Error
     std::error_code errorCode;
     std::string errorDetails;
 
-protected:
-
     /**
-     * Just here to allow derived classes to use the right constructor
-     * (the protected one).
+     * Just here to allow the static methods to use the right constructor
+     * (the private one).
      */
     struct Disambig
     {};
 
     /**
-     * Protected constructor for subclasses that provide their own error message.
-     * The error message is appended to the formatted hint.
+     * Private constructor with explicit error message string.
      */
     template<typename... Args>
     SystemError(Disambig, std::error_code errorCode, std::string_view errorDetails, Args &&... args)
@@ -284,6 +281,79 @@ public:
     {
     }
 
+    /**
+     * Construct a POSIX error using the explicitly-provided error number.
+     * `strerror` will be used to try to add additional information to the message.
+     */
+    template<typename... Args>
+    static SystemError fromPosixExplicit(int errNo, Args &&... args)
+    {
+        return SystemError(
+            Disambig{},
+            std::make_error_code(static_cast<std::errc>(errNo)),
+            strerror(errNo),
+            std::forward<Args>(args)...);
+    }
+
+    /**
+     * Construct a POSIX error using the ambient `errno`.
+     *
+     * Be sure to not perform another `errno`-modifying operation before
+     * calling this!
+     */
+    template<typename... Args>
+    static SystemError fromPosix(Args &&... args)
+    {
+        return fromPosixExplicit(errno, std::forward<Args>(args)...);
+    }
+
+#ifdef _WIN32
+    /**
+     * Construct a Windows error using the explicitly-provided error number.
+     * `FormatMessageA` will be used to try to add additional information
+     * to the message.
+     */
+    template<typename... Args>
+    static SystemError fromWindowsExplicit(DWORD lastError, Args &&... args)
+    {
+        return SystemError(
+            Disambig{},
+            std::error_code(lastError, std::system_category()),
+            renderWindowsError(lastError),
+            std::forward<Args>(args)...);
+    }
+
+    /**
+     * Construct a Windows error using `GetLastError()`.
+     *
+     * Be sure to not perform another last-error-modifying operation
+     * before calling this!
+     */
+    template<typename... Args>
+    static SystemError fromWindows(Args &&... args)
+    {
+        return fromWindowsExplicit(GetLastError(), std::forward<Args>(args)...);
+    }
+
+private:
+    static std::string renderWindowsError(DWORD lastError);
+
+public:
+#endif
+
+    /**
+     * Construct using the native error (errno on POSIX, GetLastError() on Windows).
+     */
+    template<typename... Args>
+    static SystemError fromNative(Args &&... args)
+    {
+#ifdef _WIN32
+        return fromWindows(std::forward<Args>(args)...);
+#else
+        return fromPosix(std::forward<Args>(args)...);
+#endif
+    }
+
     const std::error_code ec() const &
     {
         return errorCode;
@@ -296,53 +366,58 @@ public:
 };
 
 /**
- * POSIX system error, created using `errno`, `strerror` friends.
- *
- * Throw this, but prefer not to catch this, and catch `SystemError`
- * instead. This allows implementations to freely switch between this
- * and `windows::WinError` without breaking catch blocks.
- *
- * However, it is permissible to catch this and rethrow so long as
- * certain conditions are not met (e.g. to catch only if `errNo =
- * EFooBar`). In that case, try to also catch the equivalent `windows::WinError`
- * code.
- *
- * @todo Rename this to `PosixError` or similar. At this point Windows
- * support is too WIP to justify the code churn, but if it is finished
- * then a better identifier becomes moe worth it.
+ * Wrapper to avoid churn
  */
-class SysError : public SystemError
+template<typename... Args>
+SystemError SysError(int errNo, Args &&... args)
 {
-public:
-    int errNo;
+    return SystemError::fromPosixExplicit(errNo, std::forward<Args>(args)...);
+}
 
-    /**
-     * Construct using the explicitly-provided error number. `strerror`
-     * will be used to try to add additional information to the message.
-     */
-    template<typename... Args>
-    SysError(int errNo, Args &&... args)
-        : SystemError(
-              Disambig{},
-              std::make_error_code(static_cast<std::errc>(errNo)),
-              strerror(errNo),
-              std::forward<Args>(args)...)
-        , errNo(errNo)
-    {
-    }
+/**
+ * Wrapper to avoid churn
+ */
+template<typename... Args>
+SystemError SysError(Args &&... args)
+{
+    return SystemError::fromPosix(std::forward<Args>(args)...);
+}
 
-    /**
-     * Construct using the ambient `errno`.
-     *
-     * Be sure to not perform another `errno`-modifying operation before
-     * calling this constructor!
-     */
-    template<typename... Args>
-    SysError(Args &&... args)
-        : SysError(errno, std::forward<Args>(args)...)
-    {
-    }
-};
+#ifdef _WIN32
+
+namespace windows {
+
+/**
+ * Wrapper to avoid churn
+ */
+template<typename... Args>
+SystemError WinError(DWORD lastError, Args &&... args)
+{
+    return SystemError::fromWindowsExplicit(lastError, std::forward<Args>(args)...);
+}
+
+/**
+ * Wrapper to avoid churn
+ */
+template<typename... Args>
+SystemError WinError(Args &&... args)
+{
+    return SystemError::fromWindows(std::forward<Args>(args)...);
+}
+
+} // namespace windows
+
+#endif
+
+/**
+ * Convenience wrapper for when we use `errno`-based error handling
+ * on Unix, and `GetLastError()`-based error handling on Windows.
+ */
+template<typename... Args>
+SystemError NativeSysError(Args &&... args)
+{
+    return SystemError::fromNative(std::forward<Args>(args)...);
+}
 
 /**
  * Throw an exception for the purpose of checking that exception
@@ -382,69 +457,4 @@ int handleExceptions(const std::string & programName, std::function<void()> fun)
 #  define nixUnreachableWhenHardened std::unreachable
 #endif
 
-#ifdef _WIN32
-
-namespace windows {
-
-/**
- * Windows Error type.
- *
- * Unless you need to catch a specific error number, don't catch this in
- * portable code. Catch `SystemError` instead.
- */
-class WinError : public SystemError
-{
-public:
-    DWORD lastError;
-
-    /**
-     * Construct using the explicitly-provided error number.
-     * `FormatMessageA` will be used to try to add additional
-     * information to the message.
-     */
-    template<typename... Args>
-    WinError(DWORD lastError, Args &&... args)
-        : SystemError(
-              Disambig{},
-              std::error_code(lastError, std::system_category()),
-              renderError(lastError),
-              std::forward<Args>(args)...)
-        , lastError(lastError)
-    {
-    }
-
-    /**
-     * Construct using `GetLastError()` and the ambient "last error".
-     *
-     * Be sure to not perform another last-error-modifying operation
-     * before calling this constructor!
-     */
-    template<typename... Args>
-    WinError(Args &&... args)
-        : WinError(GetLastError(), std::forward<Args>(args)...)
-    {
-    }
-
-private:
-
-    static std::string renderError(DWORD lastError);
-};
-
-} // namespace windows
-
-#endif
-
-/**
- * Convenience alias for when we use a `errno`-based error handling
- * function on Unix, and `GetLastError()`-based error handling on on
- * Windows.
- */
-using NativeSysError =
-#ifdef _WIN32
-    windows::WinError
-#else
-    SysError
-#endif
-    ;
-
 } // namespace nix

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

@@ -133,11 +133,6 @@ std::string readLine(Descriptor fd, bool eofOk = false, char terminator = '\n');
  */
 void writeLine(Descriptor fd, std::string s);
 
-/**
- * Perform a blocking fsync operation on a file descriptor.
- */
-void syncDescriptor(Descriptor fd);
-
 /**
  * Options for draining a file descriptor to a sink.
  */
@@ -258,11 +253,7 @@ public:
     /**
      * Perform a blocking fsync operation.
      */
-    void fsync() const
-    {
-        if (fd != INVALID_DESCRIPTOR)
-            nix::syncDescriptor(fd);
-    }
+    void fsync() const;
 
     /**
      * Asynchronously flush to disk without blocking, if available on

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

@@ -15,7 +15,6 @@
  */
 
 #include "nix/util/file-descriptor.hh"
-#include "nix/util/file-system.hh"
 
 #include <optional>
 
@@ -34,90 +33,6 @@ namespace nix {
  */
 OsString readLinkAt(Descriptor dirFd, const CanonPath & path);
 
-/**
- * Create a symlink to a file relative to a directory file descriptor.
- *
- * On Windows, creates a file symlink. On Unix, equivalent to symlinkat.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path for the new symlink
- * @param target The symlink target (what it points to)
- *
- * @throws SystemError on any I/O errors.
- */
-void createFileSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target);
-
-/**
- * Create a symlink to a directory relative to a directory file descriptor.
- *
- * On Windows, creates a directory symlink. On Unix, equivalent to symlinkat.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path for the new symlink
- * @param target The symlink target (what it points to)
- *
- * @throws SystemError on any I/O errors.
- */
-void createDirectorySymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target);
-
-/**
- * Create a symlink relative to a directory file descriptor, detecting target type.
- *
- * On Windows, stats the target to determine whether to create a file or
- * directory symlink. Falls back to file symlink if the target does not exist.
- * On Unix, equivalent to symlinkat.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path for the new symlink
- * @param target The symlink target (what it points to)
- *
- * @throws SystemError on any I/O errors.
- */
-void createUnknownSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target);
-
-/**
- * Create a directory relative to a directory file descriptor.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path for the new directory
- *
- * @throws SystemError on any I/O errors.
- */
-void createDirectoryAt(Descriptor dirFd, const CanonPath & path);
-
-/**
- * Get status of an open file/directory handle.
- *
- * @param fd File descriptor/handle
- * @throws SystemError on I/O errors.
- */
-PosixStat fstat(Descriptor fd);
-
-/**
- * Get status of a file relative to a directory file descriptor.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path to stat
- *
- * @return nullopt if the path does not exist.
- * @throws SystemError on other I/O errors.
- *
- * @pre path.isRoot() is false
- */
-std::optional<PosixStat> maybeFstatat(Descriptor dirFd, const CanonPath & path);
-
-/**
- * Get status of a file relative to a directory file descriptor.
- *
- * @param dirFd Directory file descriptor
- * @param path Relative path to stat
- *
- * @throws SystemError if the path does not exist or on other I/O errors.
- *
- * @pre path.isRoot() is false
- */
-PosixStat fstatat(Descriptor dirFd, const CanonPath & path);
-
 /**
  * Safe(r) function to open a file relative to dirFd, while
  * disallowing escaping from a directory and any symlinks in the process.
@@ -182,7 +97,7 @@ namespace unix {
  * AT_SYMLINK_NOFOLLOW, since it's the best we can do without failing.
  *
  * @pre path.isRoot() is false
- * @throws SysError if any operation fails
+ * @throws SystemError if any operation fails
  */
 void fchmodatTryNoFollow(Descriptor dirFd, const CanonPath & path, mode_t mode);
 

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

@@ -28,20 +28,11 @@
  * Polyfill for MinGW
  *
  * Windows does in fact support symlinks, but the C runtime interfaces predate this.
- * We define S_IFLNK and S_ISLNK so that our lstat implementation can properly
- * indicate symlinks by setting these mode bits when it detects a reparse point.
+ *
+ * @todo get rid of this, and stop using `stat` when we want `lstat` too.
  */
-#ifndef S_IFLNK
-#  ifndef _WIN32
-#    error "S_IFLNK should be defined on non-Windows platforms"
-#  endif
-#  define S_IFLNK 0120000
-#endif
 #ifndef S_ISLNK
-#  ifndef _WIN32
-#    error "S_ISLNK should be defined on non-Windows platforms"
-#  endif
-#  define S_ISLNK(m) (((m) & S_IFMT) == S_IFLNK)
+#  define S_ISLNK(m) false
 #endif
 
 namespace nix {
@@ -134,38 +125,6 @@ using PosixStat =
 #endif
     ;
 
-#ifdef _WIN32
-namespace windows {
-
-/**
- * Convert Windows FILETIME to Unix time_t.
- */
-time_t fileTimeToUnixTime(const FILETIME & ft);
-
-/**
- * Fill a PosixStat structure from file attributes and timestamps.
- *
- * @param dwFileAttributes File attributes (FILE_ATTRIBUTE_*)
- * @param ftCreationTime Creation time
- * @param ftLastAccessTime Last access time
- * @param ftLastWriteTime Last write time
- * @param nFileSizeHigh High 32 bits of file size
- * @param nFileSizeLow Low 32 bits of file size
- * @param nNumberOfLinks Number of hard links (default 1)
- */
-void statFromFileInfo(
-    PosixStat & st,
-    DWORD dwFileAttributes,
-    const FILETIME & ftCreationTime,
-    const FILETIME & ftLastAccessTime,
-    const FILETIME & ftLastWriteTime,
-    DWORD nFileSizeHigh,
-    DWORD nFileSizeLow,
-    DWORD nNumberOfLinks = 1);
-
-} // namespace windows
-#endif
-
 /**
  * Get status of `path`.
  */
@@ -174,6 +133,10 @@ PosixStat lstat(const std::filesystem::path & path);
  * Get status of `path` following symlinks.
  */
 PosixStat stat(const std::filesystem::path & path);
+/**
+ * Get status of an open file descriptor.
+ */
+PosixStat fstat(int fd);
 /**
  * `lstat` the given path if it exists.
  * @return std::nullopt if the path doesn't exist, or an optional containing the result of `lstat` otherwise
@@ -236,16 +199,14 @@ std::filesystem::path readLink(const std::filesystem::path & path);
  *
  * @note this function will clobber `errno` (Unix) / "last error"
  * (Windows), so care must be used to get those error codes, then call
- * this, then build a `SysError` / `WinError` with the saved error code.
+ * this, then build a `SystemError` with the saved error code.
  */
 std::filesystem::path descriptorToPath(Descriptor fd);
 
 /**
  * Open a `Descriptor` with read-only access to the given directory.
- *
- * @param followSymlinks If false, fail if the path is a symlink.
  */
-Descriptor openDirectory(const std::filesystem::path & path, bool followFinalSymlink = true);
+Descriptor openDirectory(const std::filesystem::path & path);
 
 /**
  * Open a `Descriptor` with read-only access to the given file.
@@ -305,7 +266,8 @@ writeFile(const std::filesystem::path & path, Source & source, mode_t mode = 066
     return writeFile(path.string(), source, mode, sync);
 }
 
-void writeFile(Descriptor fd, std::string_view s, FsSync sync = FsSync::No, const Path * origPath = nullptr);
+void writeFile(
+    AutoCloseFD & fd, const Path & origPath, std::string_view s, mode_t mode = 0666, FsSync sync = FsSync::No);
 
 /**
  * Flush a path's parent directory to disk.

src/libutil/include/nix/util/meson.build

@@ -32,7 +32,6 @@ headers = [ config_pub_h ] + files(
   'configuration.hh',
   'current-process.hh',
   'demangle.hh',
-  'directory-source-accessor.hh',
   'english.hh',
   'environment-variables.hh',
   'error.hh',

src/libutil/include/nix/util/posix-source-accessor.hh

@@ -82,8 +82,6 @@ public:
 
     void invalidateCache(const CanonPath & path) override;
 
-    static Stat makeStat(const struct ::stat st);
-
 private:
 
     /**

src/libutil/linux/linux-namespaces.cc

@@ -40,7 +40,7 @@ bool userNamespacesSupported()
 
             auto r = pid.wait();
             assert(!r);
-        } catch (SysError & e) {
+        } catch (SystemError & e) {
             debug("user namespaces do not work on this system: %s", e.msg());
             return false;
         }
@@ -77,7 +77,7 @@ bool mountAndPidNamespacesSupported()
                 return false;
             }
 
-        } catch (SysError & e) {
+        } catch (SystemError & e) {
             debug("mount namespaces do not work on this system: %s", e.msg());
             return false;
         }

src/libutil/meson.build

@@ -139,7 +139,6 @@ sources = [ config_priv_h ] + files(
   'config-global.cc',
   'configuration.cc',
   'current-process.cc',
-  'directory-source-accessor.cc',
   'english.cc',
   'environment-variables.cc',
   'error.cc',
@@ -148,7 +147,6 @@ sources = [ config_priv_h ] + files(
   'experimental-features.cc',
   'file-content-address.cc',
   'file-descriptor.cc',
-  'file-system-at.cc',
   'file-system.cc',
   'fs-sink.cc',
   'git.cc',

src/libutil/posix-source-accessor.cc

@@ -1,5 +1,4 @@
 #include "nix/util/posix-source-accessor.hh"
-#include "nix/util/directory-source-accessor.hh"
 #include "nix/util/source-path.hh"
 #include "nix/util/signals.hh"
 #include "nix/util/sync.hh"
@@ -109,7 +108,22 @@ std::optional<SourceAccessor::Stat> PosixSourceAccessor::maybeLstat(const CanonP
     if (trackLastModified)
         mtime = std::max(mtime, st->st_mtime);
 
-    return makeStat(*st);
+    return Stat{
+        .type = S_ISREG(st->st_mode)   ? tRegular
+                : S_ISDIR(st->st_mode) ? tDirectory
+                : S_ISLNK(st->st_mode) ? tSymlink
+                : S_ISCHR(st->st_mode) ? tChar
+                : S_ISBLK(st->st_mode) ? tBlock
+                :
+#ifdef S_ISSOCK
+                S_ISSOCK(st->st_mode) ? tSocket
+                :
+#endif
+                S_ISFIFO(st->st_mode) ? tFifo
+                                      : tUnknown,
+        .fileSize = S_ISREG(st->st_mode) ? std::optional<uint64_t>(st->st_size) : std::nullopt,
+        .isExecutable = S_ISREG(st->st_mode) && st->st_mode & S_IXUSR,
+    };
 }
 
 SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath & path)
@@ -186,26 +200,6 @@ void PosixSourceAccessor::assertNoSymlinks(CanonPath path)
     }
 }
 
-PosixSourceAccessor::Stat PosixSourceAccessor::makeStat(const struct ::stat st)
-{
-    return Stat{
-        .type = S_ISREG(st.st_mode)   ? tRegular
-                : S_ISDIR(st.st_mode) ? tDirectory
-                : S_ISLNK(st.st_mode) ? tSymlink
-                : S_ISCHR(st.st_mode) ? tChar
-                : S_ISBLK(st.st_mode) ? tBlock
-                :
-#ifdef S_ISSOCK
-                S_ISSOCK(st.st_mode) ? tSocket
-                :
-#endif
-                S_ISFIFO(st.st_mode) ? tFifo
-                                     : tUnknown,
-        .fileSize = S_ISREG(st.st_mode) ? std::optional<uint64_t>(st.st_size) : std::nullopt,
-        .isExecutable = S_ISREG(st.st_mode) && st.st_mode & S_IXUSR,
-    };
-}
-
 ref<SourceAccessor> getFSSourceAccessor()
 {
     static auto rootFS = make_ref<PosixSourceAccessor>();
@@ -214,30 +208,6 @@ ref<SourceAccessor> getFSSourceAccessor()
 
 ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root, bool trackLastModified)
 {
-    AutoCloseFD fd = toDescriptor(
-        ::open(
-            root.c_str(),
-            O_RDONLY |
-#ifndef _WIN32
-                O_NOFOLLOW | O_CLOEXEC
-#endif
-            ));
-
-    if (!fd) {
-        if (errno == ELOOP)
-            /* Use a plain old PosixSourceAccessor for symlinks. Should probably just
-               read the link here into a MemorySourceAccessor. */
-            return make_ref<PosixSourceAccessor>(std::move(root), trackLastModified);
-        throw SysError("opening file %s", PathFmt(root));
-    }
-
-    struct ::stat st;
-    if (::fstat(fd.get(), &st))
-        throw SysError("getting status of %s", PathFmt(root));
-
-    if (S_ISDIR(st.st_mode))
-        return makeDirectorySourceAccessor(std::move(fd), std::move(root), trackLastModified);
-
     return make_ref<PosixSourceAccessor>(std::move(root), trackLastModified);
 }
 } // namespace nix

src/libutil/unix-domain-socket.cc

@@ -78,8 +78,8 @@ bindConnectProcHelper(std::string_view operationName, auto && operation, Socket
                 if (operation(fd, psaddr, sizeof(addr)) == -1)
                     throw SysError("cannot %s to socket at '%s'", operationName, path);
                 writeFull(pipe.writeSide.get(), "0\n");
-            } catch (SysError & e) {
-                writeFull(pipe.writeSide.get(), fmt("%d\n", e.errNo));
+            } catch (SystemError & e) {
+                writeFull(pipe.writeSide.get(), fmt("%d\n", e.ec().value()));
             } catch (...) {
                 writeFull(pipe.writeSide.get(), "-1\n");
             }

src/libutil/unix/file-descriptor.cc

@@ -1,5 +1,4 @@
 #include "nix/util/file-system.hh"
-#include "nix/util/file-system-at.hh"
 #include "nix/util/signals.hh"
 #include "nix/util/finally.hh"
 #include "nix/util/serialise.hh"
@@ -189,7 +188,7 @@ void unix::closeExtraFDs()
             }
         }
         return;
-    } catch (SysError &) {
+    } catch (SystemError &) {
     }
 #endif
 
@@ -208,17 +207,4 @@ void unix::closeOnExec(int fd)
         throw SysError("setting close-on-exec flag");
 }
 
-void syncDescriptor(Descriptor fd)
-{
-    int result =
-#if defined(__APPLE__)
-        ::fcntl(fd, F_FULLFSYNC)
-#else
-        ::fsync(fd)
-#endif
-        ;
-    if (result == -1)
-        throw NativeSysError("fsync file descriptor %1%", fd);
-}
-
 } // namespace nix

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

@@ -23,8 +23,6 @@
 #  define HAVE_FCHMODAT2 0
 #endif
 
-#include "util-unix-config-private.hh"
-
 namespace nix {
 
 #ifdef __linux__
@@ -92,9 +90,10 @@ void unix::fchmodatTryNoFollow(Descriptor dirFd, const CanonPath & path, mode_t
             PathFmt(descriptorToPath(dirFd) / path.rel()));
     }
 
-    /* Possible to use with O_PATH fd since
-     * https://github.com/torvalds/linux/commit/55815f70147dcfa3ead5738fd56d3574e2e3c1c2 (3.6) */
-    auto st = fstat(pathFd.get());
+    struct ::stat st;
+    /* Possible since https://github.com/torvalds/linux/commit/55815f70147dcfa3ead5738fd56d3574e2e3c1c2 (3.6) */
+    if (::fstat(pathFd.get(), &st) == -1)
+        throw SysError("statting '%s' relative to parent directory via O_PATH file descriptor", path.rel());
 
     if (S_ISLNK(st.st_mode))
         throw SysError(EOPNOTSUPP, "can't change mode of symlink %s", PathFmt(descriptorToPath(dirFd) / path.rel()));
@@ -172,7 +171,8 @@ openFileEnsureBeneathNoSymlinksIterative(Descriptor dirFd, const CanonPath & pat
             });
 
             if (errno == ENOTDIR) /* Path component might be a symlink. */ {
-                if (auto st = maybeFstatat(getParentFd(), CanonPath(component)); st && S_ISLNK(st->st_mode))
+                struct ::stat st;
+                if (::fstatat(getParentFd(), component.c_str(), &st, AT_SYMLINK_NOFOLLOW) == 0 && S_ISLNK(st.st_mode))
                     throw SymlinkNotAllowed(path2);
                 errno = ENOTDIR; /* Restore the errno. */
             } else if (errno == ELOOP) {
@@ -224,61 +224,4 @@ OsString readLinkAt(Descriptor dirFd, const CanonPath & path)
     }
 }
 
-static void symlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-    if (::symlinkat(target.c_str(), dirFd, path.rel_c_str()) == -1) {
-        auto savedErrno = errno;
-        throw SysError(
-            savedErrno, "creating symlink %1% -> %2%", PathFmt(descriptorToPath(dirFd) / path.rel()), target);
-    }
-}
-
-void createFileSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    symlinkAt(dirFd, path, target);
-}
-
-void createDirectorySymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    symlinkAt(dirFd, path, target);
-}
-
-void createUnknownSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    symlinkAt(dirFd, path, target);
-}
-
-void createDirectoryAt(Descriptor dirFd, const CanonPath & path)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-    if (::mkdirat(dirFd, path.rel_c_str(), 0777) == -1) {
-        auto savedErrno = errno;
-        throw SysError(savedErrno, "creating directory %1%", PathFmt(descriptorToPath(dirFd) / path.rel()));
-    }
-}
-
-PosixStat fstat(Descriptor fd)
-{
-    PosixStat st;
-    if (::fstat(fd, &st)) {
-        auto savedErrno = errno;
-        throw SysError(savedErrno, "getting status of %s", PathFmt(descriptorToPath(fd)));
-    }
-    return st;
-}
-
-PosixStat fstatat(Descriptor dirFd, const CanonPath & path)
-{
-    assert(!path.isRoot());
-    PosixStat st;
-    if (::fstatat(dirFd, path.rel_c_str(), &st, AT_SYMLINK_NOFOLLOW)) {
-        auto savedErrno = errno;
-        throw SysError(savedErrno, "getting status of %s", PathFmt(descriptorToPath(dirFd) / path.rel()));
-    }
-    return st;
-}
-
 } // namespace nix

src/libutil/unix/file-system.cc

@@ -23,9 +23,9 @@
 
 namespace nix {
 
-Descriptor openDirectory(const std::filesystem::path & path, bool followFinalSymlink)
+Descriptor openDirectory(const std::filesystem::path & path)
 {
-    return open(path.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC | (followFinalSymlink ? 0 : O_NOFOLLOW));
+    return open(path.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC);
 }
 
 Descriptor openFileReadonly(const std::filesystem::path & path)
@@ -76,14 +76,6 @@ std::filesystem::path defaultTempDir()
     return getEnvNonEmpty("TMPDIR").value_or("/tmp");
 }
 
-PosixStat lstat(const std::filesystem::path & path)
-{
-    PosixStat st;
-    if (::lstat(path.c_str(), &st))
-        throw SysError("getting status of %s", PathFmt(path));
-    return st;
-}
-
 void setWriteTime(
     const std::filesystem::path & path, time_t accessedTime, time_t modificationTime, std::optional<bool> optIsSymlink)
 {
@@ -194,9 +186,9 @@ static void _deletePath(
         if ((st.st_mode & PERM_MASK) != PERM_MASK)
             try {
                 unix::fchmodatTryNoFollow(parentfd, CanonPath(name), st.st_mode | PERM_MASK);
-            } catch (SysError & e) {
+            } catch (SystemError & e) {
                 e.addTrace({}, "while making directory %1% accessible for deletion", PathFmt(path));
-                if (e.errNo == EOPNOTSUPP)
+                if (e.is(std::errc::operation_not_supported))
                     e.addTrace({}, "%1% is now a symlink, expected directory", PathFmt(path));
                 throw;
             }

src/libutil/unix/include/nix/util/monitor-fd.hh

@@ -60,7 +60,7 @@ inline void MonitorFdHup::runThread(int watchFd, int notifyFd)
 {
     int kqResult = kqueue();
     if (kqResult < 0) {
-        throw SysError("MonitorFdHup kqueue");
+        throw SystemError::fromPosix("MonitorFdHup kqueue");
     }
     AutoCloseFD kq{kqResult};
 
@@ -78,14 +78,14 @@ inline void MonitorFdHup::runThread(int watchFd, int notifyFd)
 
     int result = kevent(kq.get(), kevs.data(), kevs.size(), nullptr, 0, nullptr);
     if (result < 0) {
-        throw SysError("MonitorFdHup kevent add");
+        throw SystemError::fromPosix("MonitorFdHup kevent add");
     }
 
     while (true) {
         struct kevent event;
         int numEvents = kevent(kq.get(), nullptr, 0, &event, 1, nullptr);
         if (numEvents < 0) {
-            throw SysError("MonitorFdHup kevent watch");
+            throw SystemError::fromPosix("MonitorFdHup kevent watch");
         }
 
         if (numEvents > 0 && (event.flags & EV_EOF)) {
@@ -112,7 +112,7 @@ inline void MonitorFdHup::runThread(int watchFd, int notifyFd)
             if (errno == EINTR || errno == EAGAIN) {
                 continue;
             } else {
-                throw SysError("in MonitorFdHup poll()");
+                throw SystemError::fromPosix("in MonitorFdHup poll()");
             }
         }
 

src/libutil/unix/users.cc

@@ -39,7 +39,7 @@ std::filesystem::path getHome()
                 auto st = maybeStat(homeDir->c_str());
                 if (st && st->st_uid != geteuid())
                     unownedUserHomeDir.swap(homeDir);
-            } catch (SysError & e) {
+            } catch (SystemError & e) {
                 warn(
                     "couldn't stat $HOME ('%s') for reason other than not existing, falling back to the one defined in the 'passwd' file: %s",
                     *homeDir,

src/libutil/windows/current-process.cc

@@ -8,6 +8,8 @@
 
 namespace nix {
 
+using namespace nix::windows;
+
 std::chrono::microseconds getCpuUserTime()
 {
     FILETIME creationTime;
@@ -17,7 +19,7 @@ std::chrono::microseconds getCpuUserTime()
 
     if (!GetProcessTimes(GetCurrentProcess(), &creationTime, &exitTime, &kernelTime, &userTime)) {
         auto lastError = GetLastError();
-        throw windows::WinError(lastError, "failed to get CPU time");
+        throw WinError(lastError, "failed to get CPU time");
     }
 
     ULARGE_INTEGER uLargeInt;

src/libutil/windows/file-descriptor.cc

@@ -148,10 +148,4 @@ off_t lseek(HANDLE h, off_t offset, int whence)
     return newPos.QuadPart;
 }
 
-void syncDescriptor(Descriptor fd)
-{
-    if (!::FlushFileBuffers(fd))
-        throw WinError("FlushFileBuffers file descriptor %1%", fd);
-}
-
 } // namespace nix

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

@@ -4,9 +4,8 @@
 #include "nix/util/file-path.hh"
 #include "nix/util/source-accessor.hh"
 
-#include <span>
-
 #include <fileapi.h>
+#include <error.h>
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <winioctl.h>
@@ -14,8 +13,6 @@
 
 namespace nix {
 
-using namespace nix::windows;
-
 namespace windows {
 
 namespace {
@@ -89,8 +86,8 @@ HANDLE openSymlinkAt(Descriptor dirFd, const CanonPath & path)
     assert(!path.isRoot());
     assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
 
-    auto wpath = std::filesystem::path(path.rel()).make_preferred();
-    return ntOpenAt(dirFd, wpath.c_str(), FILE_READ_ATTRIBUTES | SYNCHRONIZE, FILE_OPEN_REPARSE_POINT);
+    std::wstring wpath = string_to_os_string(path.rel());
+    return ntOpenAt(dirFd, wpath, FILE_READ_ATTRIBUTES | SYNCHRONIZE, FILE_OPEN_REPARSE_POINT);
 }
 
 /**
@@ -192,54 +189,6 @@ OsString readSymlinkTarget(HANDLE linkHandle)
     return {target_start, target_len};
 }
 
-/**
- * Write symlink target to an open file handle using reparse point.
- *
- * @param handle Open file handle (must have GENERIC_WRITE access)
- * @param target The symlink target (what it points to)
- */
-void writeSymlinkTarget(HANDLE handle, const std::filesystem::path & target)
-{
-    /* Build the reparse data buffer for a symbolic link.
-       Layout: SubstituteName and PrintName stored consecutively in PathBuffer.
-       We use the same string for both. */
-    size_t targetBytes = target.native().size() * sizeof(wchar_t);
-    size_t bufSize = offsetof(ReparseDataBuffer, SymbolicLinkReparseBuffer.PathBuffer) + targetBytes * 2;
-    std::vector<uint8_t> buf(bufSize, 0);
-
-    auto * reparse = reinterpret_cast<ReparseDataBuffer *>(buf.data());
-    reparse->ReparseTag = IO_REPARSE_TAG_SYMLINK;
-    reparse->ReparseDataLength =
-        static_cast<unsigned short>(bufSize - offsetof(ReparseDataBuffer, SymbolicLinkReparseBuffer));
-    reparse->Reserved = 0;
-
-    auto & symlink = reparse->SymbolicLinkReparseBuffer;
-    /* SubstituteName comes first */
-    symlink.SubstituteNameOffset = 0;
-    symlink.SubstituteNameLength = static_cast<unsigned short>(targetBytes);
-    /* PrintName follows SubstituteName */
-    symlink.PrintNameOffset = static_cast<unsigned short>(targetBytes);
-    symlink.PrintNameLength = static_cast<unsigned short>(targetBytes);
-    /* SYMLINK_FLAG_RELATIVE = 1 for relative symlinks, 0 for absolute */
-    symlink.Flags = target.is_relative() ? 1 : 0;
-
-    /* Copy target into PathBuffer twice (SubstituteName and PrintName) */
-    memcpy(symlink.PathBuffer, target.c_str(), targetBytes);
-    memcpy(reinterpret_cast<char *>(symlink.PathBuffer) + targetBytes, target.c_str(), targetBytes);
-
-    DWORD bytesReturned;
-    if (!DeviceIoControl(
-            handle,
-            FSCTL_SET_REPARSE_POINT,
-            buf.data(),
-            static_cast<DWORD>(bufSize),
-            nullptr,
-            0,
-            &bytesReturned,
-            nullptr))
-        throw WinError("setting reparse point for symlink");
-}
-
 /**
  * Check if a handle refers to a reparse point (e.g., symlink).
  *
@@ -259,114 +208,7 @@ bool isReparsePoint(HANDLE handle)
 
 } // namespace windows
 
-OsString readLinkAt(Descriptor dirFd, const CanonPath & path)
-{
-    AutoCloseFD linkHandle(openSymlinkAt(dirFd, path));
-    return readSymlinkTarget(linkHandle.get());
-}
-
-void createFileSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-
-    auto wpath = std::filesystem::path(path.rel()).make_preferred();
-
-    /* Create the file that will become the symlink */
-    AutoCloseFD handle(ntOpenAt(
-        dirFd, wpath.c_str(), GENERIC_WRITE | DELETE, FILE_NON_DIRECTORY_FILE | FILE_OPEN_REPARSE_POINT, FILE_CREATE));
-
-    writeSymlinkTarget(handle.get(), target);
-}
-
-void createDirectorySymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-
-    auto wpath = std::filesystem::path(path.rel()).make_preferred();
-
-    /* Create the directory that will become the symlink */
-    AutoCloseFD handle(ntOpenAt(
-        dirFd, wpath.c_str(), GENERIC_WRITE | DELETE, FILE_DIRECTORY_FILE | FILE_OPEN_REPARSE_POINT, FILE_CREATE));
-
-    writeSymlinkTarget(handle.get(), target);
-}
-
-void createUnknownSymlinkAt(Descriptor dirFd, const CanonPath & path, const OsString & target)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-
-    /* Resolve target path to determine if it's a directory.
-       Target is relative to the symlink's parent directory. */
-    std::filesystem::path targetPath(target);
-    std::filesystem::path resolvedTarget;
-
-    if (targetPath.is_absolute()) {
-        resolvedTarget = targetPath;
-    } else {
-        /* Get the symlink's parent directory path and resolve target relative to it */
-        auto symlinkDir = descriptorToPath(dirFd);
-        if (auto parent = path.parent())
-            symlinkDir /= parent->rel();
-        resolvedTarget = symlinkDir / targetPath;
-    }
-
-    /* Check if target is a directory. If we can't stat it (e.g., dangling symlink),
-       fall back to file symlink. */
-    std::error_code ec;
-    auto status = std::filesystem::status(resolvedTarget, ec);
-    bool isDirectory = !ec && std::filesystem::is_directory(status);
-
-    if (isDirectory)
-        createDirectorySymlinkAt(dirFd, path, target);
-    else
-        createFileSymlinkAt(dirFd, path, target);
-}
-
-void createDirectoryAt(Descriptor dirFd, const CanonPath & path)
-{
-    assert(!path.isRoot());
-    assert(!path.rel().starts_with('/')); /* Just in case the invariant is somehow broken. */
-
-    auto wpath = std::filesystem::path(path.rel()).make_preferred();
-
-    /* Create the directory. The handle is immediately closed. */
-    AutoCloseFD handle(ntOpenAt(dirFd, wpath.c_str(), FILE_TRAVERSE | SYNCHRONIZE, FILE_DIRECTORY_FILE, FILE_CREATE));
-}
-
-PosixStat fstat(Descriptor fd)
-{
-    BY_HANDLE_FILE_INFORMATION info;
-    if (!GetFileInformationByHandle(fd, &info))
-        throw WinError("getting file information for %s", PathFmt(descriptorToPath(fd)));
-
-    PosixStat st;
-    windows::statFromFileInfo(
-        st,
-        info.dwFileAttributes,
-        info.ftCreationTime,
-        info.ftLastAccessTime,
-        info.ftLastWriteTime,
-        info.nFileSizeHigh,
-        info.nFileSizeLow,
-        info.nNumberOfLinks);
-
-    return st;
-}
-
-PosixStat fstatat(Descriptor dirFd, const CanonPath & path)
-{
-    assert(!path.isRoot());
-
-    auto wpath = std::filesystem::path(path.rel()).make_preferred();
-
-    /* Open the file without following symlinks */
-    AutoCloseFD handle(ntOpenAt(dirFd, wpath.c_str(), FILE_READ_ATTRIBUTES | SYNCHRONIZE, FILE_OPEN_REPARSE_POINT));
-
-    return fstat(handle.get());
-}
+using namespace nix::windows;
 
 Descriptor openFileEnsureBeneathNoSymlinks(
     Descriptor dirFd, const CanonPath & path, ACCESS_MASK desiredAccess, ULONG createOptions, ULONG createDisposition)
@@ -417,9 +259,10 @@ Descriptor openFileEnsureBeneathNoSymlinks(
                 FILE_TRAVERSE | SYNCHRONIZE,                  // Just need traversal rights
                 FILE_DIRECTORY_FILE | FILE_OPEN_REPARSE_POINT // Open directory, don't follow symlinks
             );
-        } catch (WinError & e) {
+        } catch (SystemError & e) {
             /* Check if this is because it's a symlink */
-            if (e.lastError == ERROR_CANT_ACCESS_FILE || e.lastError == ERROR_ACCESS_DENIED) {
+            auto err = e.ec().value();
+            if (err == ERROR_CANT_ACCESS_FILE || err == ERROR_ACCESS_DENIED) {
                 throwIfSymlink(wcomponent, pathUpTo(std::next(it)));
             }
             throw;
@@ -444,9 +287,9 @@ Descriptor openFileEnsureBeneathNoSymlinks(
             desiredAccess,
             createOptions | FILE_OPEN_REPARSE_POINT, // Don't follow symlinks on final component either
             createDisposition);
-    } catch (WinError & e) {
+    } catch (SystemError & e) {
         /* Check if final component is a symlink when we requested to not follow it */
-        if (e.lastError == ERROR_CANT_ACCESS_FILE) {
+        if (e.ec().value() == ERROR_CANT_ACCESS_FILE) {
             throwIfSymlink(finalComponent, path);
         }
         throw;
@@ -459,4 +302,10 @@ Descriptor openFileEnsureBeneathNoSymlinks(
     return finalHandle;
 }
 
+OsString readLinkAt(Descriptor dirFd, const CanonPath & path)
+{
+    AutoCloseFD linkHandle(windows::openSymlinkAt(dirFd, path));
+    return windows::readSymlinkTarget(linkHandle.get());
+}
+
 } // namespace nix

src/libutil/windows/file-system.cc

@@ -23,7 +23,7 @@ void setWriteTime(
     warn("Changing file times is not yet implemented on Windows, path is %s", PathFmt(path));
 }
 
-Descriptor openDirectory(const std::filesystem::path & path, bool followFinalSymlink)
+Descriptor openDirectory(const std::filesystem::path & path)
 {
     return CreateFileW(
         path.c_str(),
@@ -31,7 +31,7 @@ Descriptor openDirectory(const std::filesystem::path & path, bool followFinalSym
         FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
         /*lpSecurityAttributes=*/nullptr,
         OPEN_EXISTING,
-        FILE_FLAG_BACKUP_SEMANTICS | (followFinalSymlink ? 0 : FILE_FLAG_OPEN_REPARSE_POINT),
+        FILE_FLAG_BACKUP_SEMANTICS,
         /*hTemplateFile=*/nullptr);
 }
 
@@ -105,67 +105,4 @@ std::filesystem::path descriptorToPath(Descriptor handle)
     return std::filesystem::path{std::wstring{buf.data(), dw}};
 }
 
-time_t windows::fileTimeToUnixTime(const FILETIME & ft)
-{
-    /* FILETIME is 100-nanosecond intervals since January 1, 1601 UTC.
-       Unix time is seconds since January 1, 1970 UTC.
-       Difference is 11644473600 seconds. */
-    ULARGE_INTEGER ull;
-    ull.LowPart = ft.dwLowDateTime;
-    ull.HighPart = ft.dwHighDateTime;
-    return static_cast<time_t>(ull.QuadPart / 10000000ULL - 11644473600ULL);
-}
-
-void windows::statFromFileInfo(
-    PosixStat & st,
-    DWORD dwFileAttributes,
-    const FILETIME & ftCreationTime,
-    const FILETIME & ftLastAccessTime,
-    const FILETIME & ftLastWriteTime,
-    DWORD nFileSizeHigh,
-    DWORD nFileSizeLow,
-    DWORD nNumberOfLinks)
-{
-    memset(&st, 0, sizeof(st));
-
-    /* Determine file type */
-    if (dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
-        st.st_mode = S_IFLNK | 0777;
-    } else if (dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
-        st.st_mode = S_IFDIR | 0755;
-    } else {
-        st.st_mode = S_IFREG | 0644;
-    }
-
-    /* File size (only meaningful for regular files) */
-    st.st_size = (static_cast<int64_t>(nFileSizeHigh) << 32) | nFileSizeLow;
-
-    /* Timestamps */
-    st.st_atime = fileTimeToUnixTime(ftLastAccessTime);
-    st.st_mtime = fileTimeToUnixTime(ftLastWriteTime);
-    st.st_ctime = fileTimeToUnixTime(ftCreationTime);
-
-    st.st_nlink = nNumberOfLinks;
-    st.st_uid = 0;
-    st.st_gid = 0;
-}
-
-PosixStat lstat(const std::filesystem::path & path)
-{
-    WIN32_FILE_ATTRIBUTE_DATA attrData;
-    if (!GetFileAttributesExW(path.c_str(), GetFileExInfoStandard, &attrData))
-        throw WinError("getting status of %s", PathFmt(path));
-
-    PosixStat st;
-    windows::statFromFileInfo(
-        st,
-        attrData.dwFileAttributes,
-        attrData.ftCreationTime,
-        attrData.ftLastAccessTime,
-        attrData.ftLastWriteTime,
-        attrData.nFileSizeHigh,
-        attrData.nFileSizeLow);
-    return st;
-}
-
 } // namespace nix

src/libutil/windows/known-folders.cc

@@ -8,8 +8,6 @@
 
 namespace nix::windows::known_folders {
 
-using namespace nix::windows;
-
 static std::filesystem::path getKnownFolder(REFKNOWNFOLDERID rfid)
 {
     PWSTR str = nullptr;

src/libutil/windows/muxable-pipe.cc

@@ -7,15 +7,17 @@
 
 namespace nix {
 
+using namespace nix::windows;
+
 void MuxablePipePollState::poll(HANDLE ioport, std::optional<unsigned int> timeout)
 {
     /* We are on at least Windows Vista / Server 2008 and can get many
        (countof(oentries)) statuses in one API call. */
     if (!GetQueuedCompletionStatusEx(
             ioport, oentries, sizeof(oentries) / sizeof(*oentries), &removed, timeout ? *timeout : INFINITE, false)) {
-        windows::WinError winError("GetQueuedCompletionStatusEx");
-        if (winError.lastError != WAIT_TIMEOUT)
-            throw winError;
+        auto lastError = GetLastError();
+        if (lastError != WAIT_TIMEOUT)
+            throw WinError(lastError, "GetQueuedCompletionStatusEx");
         assert(removed == 0);
     } else {
         assert(0 < removed && removed <= sizeof(oentries) / sizeof(*oentries));
@@ -52,12 +54,12 @@ void MuxablePipePollState::iterate(
                         // here is possible (but not obligatory) to call
                         // `handleRead` and repeat ReadFile immediately
                     } else {
-                        windows::WinError winError("ReadFile(%s, ..)", (*p)->readSide.get());
-                        if (winError.lastError == ERROR_BROKEN_PIPE) {
+                        auto lastError = GetLastError();
+                        if (lastError == ERROR_BROKEN_PIPE) {
                             handleEOF((*p)->readSide.get());
                             nextp = channels.erase(p); // no need to maintain `channels` ?
-                        } else if (winError.lastError != ERROR_IO_PENDING)
-                            throw winError;
+                        } else if (lastError != ERROR_IO_PENDING)
+                            throw WinError(lastError, "ReadFile(%s, ..)", (*p)->readSide.get());
                     }
                 }
                 break;

src/libutil/windows/windows-error.cc

@@ -6,9 +6,9 @@
 #  define WIN32_LEAN_AND_MEAN
 #  include <windows.h>
 
-namespace nix::windows {
+namespace nix {
 
-std::string WinError::renderError(DWORD lastError)
+std::string SystemError::renderWindowsError(DWORD lastError)
 {
     LPSTR errorText = NULL;
 
@@ -32,5 +32,5 @@ std::string WinError::renderError(DWORD lastError)
     return fmt("CODE=%d", lastError);
 }
 
-} // namespace nix::windows
+} // namespace nix
 #endif

src/nix/man-pages.cc

@@ -17,7 +17,7 @@ void showManPage(const std::string & name)
     setEnv("MANPATH", (getNixManDir().string() + ":").c_str());
     execlp("man", "man", name.c_str(), nullptr);
     if (errno == ENOENT) {
-        // Not SysError because we don't want to suffix the errno, aka No such file or directory.
+        // Not SystemError because we don't want to suffix the errno, aka No such file or directory.
         throw Error(
             "The '%1%' command was not found, but it is needed for '%2%' and some other '%3%' commands' help text. Perhaps you could install the '%1%' command?",
             "man",