Use std::filesystem functions in more places

This makes for shorter and more portable code.

The only tricky part is catching exceptions: I just searched for near by
`catch (Error &)` or `catch (SysError &)` and adjusted them to `catch
(std::filesystem::filesystem_error &)` according to my human judgement.

Good for windows portability; will help @siddhantk232 with his GSOC
project.

configure.ac

@@ -63,7 +63,6 @@ AC_SYS_LARGEFILE
 
 
 # Solaris-specific stuff.
-AC_STRUCT_DIRENT_D_TYPE
 case "$host_os" in
   solaris*)
     # Solaris requires -lsocket -lnsl for network functions

src/libcmd/repl.cc

@@ -264,6 +264,7 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
                     completions.insert(prev + dir + "/" + entry.name);
             }
         } catch (Error &) {
+        } catch (std::filesystem::filesystem_error &) {
         }
     } else if ((dot = cur.rfind('.')) == std::string::npos) {
         /* This is a variable name; look it up in the current scope. */

src/libstore/builtins/buildenv.cc

@@ -21,8 +21,8 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
 
     try {
         srcFiles = readDirectory(srcDir);
-    } catch (SysError & e) {
-        if (e.errNo == ENOTDIR) {
+    } catch (std::filesystem::filesystem_error & e) {
+        if (e.code() == std::errc::not_a_directory) {
             warn("not including '%s' in the user environment because it's not a directory", srcDir);
             return;
         }

src/libstore/globals.cc

@@ -348,8 +348,8 @@ void initPlugins()
             auto ents = readDirectory(pluginFile);
             for (const auto & ent : ents)
                 pluginFiles.emplace_back(pluginFile + "/" + ent.name);
-        } catch (SysError & e) {
-            if (e.errNo != ENOTDIR)
+        } catch (std::filesystem::filesystem_error & e) {
+            if (e.code() != std::errc::not_a_directory)
                 throw;
             pluginFiles.emplace_back(pluginFile);
         }

src/libstore/profiles.cc

@@ -338,6 +338,8 @@ Path getDefaultProfile()
         return absPath(readLink(profileLink), dirOf(profileLink));
     } catch (Error &) {
         return profileLink;
+    } catch (std::filesystem::filesystem_error &) {
+        return profileLink;
     }
 }
 

src/libstore/unix/gc.cc

@@ -203,7 +203,7 @@ void LocalStore::findTempRoots(Roots & tempRoots, bool censor)
 }
 
 
-void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
+void LocalStore::findRoots(const Path & path, std::filesystem::file_type type, Roots & roots)
 {
     auto foundRoot = [&](const Path & path, const Path & target) {
         try {
@@ -217,15 +217,15 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 
     try {
 
-        if (type == DT_UNKNOWN)
+        if (type == std::filesystem::file_type::unknown)
             type = getFileType(path);
 
-        if (type == DT_DIR) {
+        if (type == std::filesystem::file_type::directory) {
             for (auto & i : readDirectory(path))
                 findRoots(path + "/" + i.name, i.type, roots);
         }
 
-        else if (type == DT_LNK) {
+        else if (type == std::filesystem::file_type::symlink) {
             Path target = readLink(path);
             if (isInStore(target))
                 foundRoot(path, target);
@@ -247,7 +247,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
             }
         }
 
-        else if (type == DT_REG) {
+        else if (type == std::filesystem::file_type::regular) {
             auto storePath = maybeParseStorePath(storeDir + "/" + std::string(baseNameOf(path)));
             if (storePath && isValidPath(*storePath))
                 roots[std::move(*storePath)].emplace(path);
@@ -268,8 +268,8 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 void LocalStore::findRootsNoTemp(Roots & roots, bool censor)
 {
     /* Process direct roots in {gcroots,profiles}. */
-    findRoots(stateDir + "/" + gcRootsDir, DT_UNKNOWN, roots);
-    findRoots(stateDir + "/profiles", DT_UNKNOWN, roots);
+    findRoots(stateDir + "/" + gcRootsDir, std::filesystem::file_type::unknown, roots);
+    findRoots(stateDir + "/profiles", std::filesystem::file_type::unknown, roots);
 
     /* Add additional roots returned by different platforms-specific
        heuristics.  This is typically used to add running programs to

src/libstore/unix/local-store.hh

@@ -371,7 +371,7 @@ private:
     PathSet queryValidPathsOld();
     ValidPathInfo queryPathInfoOld(const Path & path);
 
-    void findRoots(const Path & path, unsigned char type, Roots & roots);
+    void findRoots(const Path & path, std::filesystem::file_type type, Roots & roots);
 
     void findRootsNoTemp(Roots & roots, bool censor);
 

src/libutil/file-system.cc

@@ -120,10 +120,10 @@ Path canonPath(PathView path, bool resolveSymlinks)
 
 Path dirOf(const PathView path)
 {
-    Path::size_type pos = path.rfind('/');
+    Path::size_type pos = NativePathTrait::rfindPathSep(path);
     if (pos == path.npos)
         return ".";
-    return pos == 0 ? "/" : Path(path, 0, pos);
+    return fs::path{path}.parent_path().string();
 }
 
 
@@ -217,72 +217,36 @@ bool pathAccessible(const Path & path)
 
 Path readLink(const Path & path)
 {
-#ifndef _WIN32
     checkInterrupt();
-    std::vector<char> buf;
-    for (ssize_t bufSize = PATH_MAX/4; true; bufSize += bufSize/2) {
-        buf.resize(bufSize);
-        ssize_t rlSize = readlink(path.c_str(), buf.data(), bufSize);
-        if (rlSize == -1)
-            if (errno == EINVAL)
-                throw Error("'%1%' is not a symlink", path);
-            else
-                throw SysError("reading symbolic link '%1%'", path);
-        else if (rlSize < bufSize)
-            return std::string(buf.data(), rlSize);
-    }
-#else
-    // TODO modern Windows does in fact support symlinks
-    throw UnimplementedError("reading symbolic link '%1%'", path);
-#endif
+    return fs::read_symlink(path).string();
 }
 
 
 bool isLink(const Path & path)
 {
-    return getFileType(path) == DT_LNK;
+    return getFileType(path) == fs::file_type::symlink;
 }
 
 
-DirEntries readDirectory(DIR *dir, const Path & path)
+DirEntries readDirectory(const Path & path)
 {
     DirEntries entries;
     entries.reserve(64);
 
-    struct dirent * dirent;
-    while (errno = 0, dirent = readdir(dir)) { /* sic */
+    for (auto & entry : fs::directory_iterator{path}) {
         checkInterrupt();
-        std::string name = dirent->d_name;
-        if (name == "." || name == "..") continue;
-        entries.emplace_back(name, dirent->d_ino,
-#ifdef HAVE_STRUCT_DIRENT_D_TYPE
-            dirent->d_type
-#else
-            DT_UNKNOWN
-#endif
-        );
+        entries.emplace_back(
+            entry.path().filename().string(),
+            entry.symlink_status().type());
     }
-    if (errno) throw SysError("reading directory '%1%'", path);
 
     return entries;
 }
 
-DirEntries readDirectory(const Path & path)
+
+fs::file_type getFileType(const Path & path)
 {
-    AutoCloseDir dir(opendir(path.c_str()));
-    if (!dir) throw SysError("opening directory '%1%'", path);
-
-    return readDirectory(dir.get(), path);
-}
-
-
-unsigned char getFileType(const Path & path)
-{
-    struct stat st = lstat(path);
-    if (S_ISDIR(st.st_mode)) return DT_DIR;
-    if (S_ISLNK(st.st_mode)) return DT_LNK;
-    if (S_ISREG(st.st_mode)) return DT_REG;
-    return DT_UNKNOWN;
+    return fs::symlink_status(path).type();
 }
 
 
@@ -432,8 +396,15 @@ static void _deletePath(Descriptor parentfd, const Path & path, uint64_t & bytes
         AutoCloseDir dir(fdopendir(fd));
         if (!dir)
             throw SysError("opening directory '%1%'", path);
-        for (auto & i : readDirectory(dir.get(), path))
-            _deletePath(dirfd(dir.get()), path + "/" + i.name, bytesFreed);
+
+        struct dirent * dirent;
+        while (errno = 0, dirent = readdir(dir.get())) { /* sic */
+            checkInterrupt();
+            std::string childName = dirent->d_name;
+            if (childName == "." || childName == "..") continue;
+            _deletePath(dirfd(dir.get()), path + "/" + childName, bytesFreed);
+        }
+        if (errno) throw SysError("reading directory '%1%'", path);
     }
 
     int flags = S_ISDIR(st.st_mode) ? AT_REMOVEDIR : 0;
@@ -611,13 +582,7 @@ std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
 
 void createSymlink(const Path & target, const Path & link)
 {
-#ifndef _WIN32
-    if (symlink(target.c_str(), link.c_str()))
-        throw SysError("creating symlink from '%1%' to '%2%'", link, target);
-#else
-    // TODO modern Windows does in fact support symlinks
-    throw UnimplementedError("createSymlink");
-#endif
+    fs::create_symlink(target, link);
 }
 
 void replaceSymlink(const Path & target, const Path & link)
@@ -627,8 +592,8 @@ void replaceSymlink(const Path & target, const Path & link)
 
         try {
             createSymlink(target, tmp);
-        } catch (SysError & e) {
-            if (e.errNo == EEXIST) continue;
+        } catch (fs::filesystem_error & e) {
+            if (e.code() == std::errc::file_exists) continue;
             throw;
         }
 

src/libutil/file-system.hh

@@ -27,13 +27,6 @@
 #include <sstream>
 #include <optional>
 
-#ifndef HAVE_STRUCT_DIRENT_D_TYPE
-#define DT_UNKNOWN 0
-#define DT_REG 1
-#define DT_LNK 2
-#define DT_DIR 3
-#endif
-
 /**
  * Polyfill for MinGW
  *
@@ -132,20 +125,16 @@ bool isLink(const Path & path);
 struct DirEntry
 {
     std::string name;
-    ino_t ino;
-    /**
-     * one of DT_*
-     */
-    unsigned char type;
-    DirEntry(std::string name, ino_t ino, unsigned char type)
-        : name(std::move(name)), ino(ino), type(type) { }
+    std::filesystem::file_type type;
+    DirEntry(std::string name, std::filesystem::file_type type)
+        : name(std::move(name)), type(type) { }
 };
 
 typedef std::vector<DirEntry> DirEntries;
 
 DirEntries readDirectory(const Path & path);
 
-unsigned char getFileType(const Path & path);
+std::filesystem::file_type getFileType(const Path & path);
 
 /**
  * Read the contents of a file into a string.

src/libutil/linux/cgroup.cc

@@ -65,7 +65,7 @@ static CgroupStats destroyCgroup(const Path & cgroup, bool returnStats)
     /* Otherwise, manually kill every process in the subcgroups and
        this cgroup. */
     for (auto & entry : readDirectory(cgroup)) {
-        if (entry.type != DT_DIR) continue;
+        if (entry.type != std::filesystem::file_type::directory) continue;
         destroyCgroup(cgroup + "/" + entry.name, false);
     }
 

src/libutil/posix-source-accessor.cc

@@ -134,13 +134,17 @@ SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath &
     DirEntries res;
     for (auto & entry : nix::readDirectory(makeAbsPath(path).string())) {
         std::optional<Type> type;
+        // cannot exhaustively enumerate because implementation-specific
+        // additional file types are allowed.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wswitch-enum"
         switch (entry.type) {
-        case DT_REG: type = Type::tRegular; break;
-    #ifndef _WIN32
-        case DT_LNK: type = Type::tSymlink; break;
-    #endif
-        case DT_DIR: type = Type::tDirectory; break;
+        case std::filesystem::file_type::regular: type = Type::tRegular; break;
+        case std::filesystem::file_type::symlink: type = Type::tSymlink; break;
+        case std::filesystem::file_type::directory: type = Type::tDirectory; break;
+        default: type = tMisc;
         }
+#pragma GCC diagnostic pop
         res.emplace(entry.name, type);
     }
     return res;

src/libutil/unix/file-descriptor.cc

@@ -133,6 +133,7 @@ void closeMostFDs(const std::set<int> & exceptions)
         }
         return;
     } catch (SysError &) {
+    } catch (std::filesystem::filesystem_error &) {
     }
 #endif
 

src/nix-collect-garbage/nix-collect-garbage.cc

@@ -31,14 +31,14 @@ void removeOldGenerations(std::string dir)
         checkInterrupt();
 
         auto path = dir + "/" + i.name;
-        auto type = i.type == DT_UNKNOWN ? getFileType(path) : i.type;
+        auto type = i.type == std::filesystem::file_type::unknown ? getFileType(path) : i.type;
 
-        if (type == DT_LNK && canWrite) {
+        if (type == std::filesystem::file_type::symlink && canWrite) {
             std::string link;
             try {
                 link = readLink(path);
-            } catch (SysError & e) {
-                if (e.errNo == ENOENT) continue;
+            } catch (std::filesystem::filesystem_error & e) {
+                if (e.code() == std::errc::no_such_file_or_directory) continue;
                 throw;
             }
             if (link.find("link") != std::string::npos) {
@@ -49,7 +49,7 @@ void removeOldGenerations(std::string dir)
                 } else
                     deleteOldGenerations(path, dryRun);
             }
-        } else if (type == DT_DIR) {
+        } else if (type == std::filesystem::file_type::directory) {
             removeOldGenerations(path);
         }
     }

src/nix/config-check.cc

@@ -107,7 +107,8 @@ struct CmdConfigCheck : StoreCommand
                     if (profileDir.find("/profiles/") == std::string::npos)
                         dirs.insert(dir);
                 }
-            } catch (SystemError &) {}
+            } catch (SystemError &) {
+            } catch (std::filesystem::filesystem_error &) {}
         }
 
         if (!dirs.empty()) {