[libc++] Reimplement the dynamic filesystem helper without using Python

[ldionne]

Summary

This patch reimplements the dynamic filesystem helper using Posix
functionality instead of relying on Python. The primary reason for
doing this is that it allows running the libc++ test suite on devices
that do not have Python.

[ldionne]

Got offline approval from Eric to land this, with the intent of doing a post-commit review.

[arichardson]

Thank you very much for working in this @ldionne ! We (the CHERI project, https://github.com/CTSRD-CHERI/llvm-project/) can only sensibly test libc++ using the SSH executor since we use FPGA and QEMU implementations of CHERI MIPS/RISCV.
So far I completely skipped the filesystem tests since our minimal test images don't contain python and I'm looking forward to being able to also run those tests.

I am currently in the process of merging from upstream LLVM and I will attempt to upstream my libc++ lit changes once I've completed that.
I've made a few changes to libc++'s lit remote SSH execution (e.g. adding a new SSHExecutor running with a NFS/SMBFS mounted directory to avoid the scp overhead) that might also be useful upstream.

[ldionne]

In D77140#1957510, @arichardson wrote:

Thank you very much for working in this @ldionne ! We (the CHERI project, https://github.com/CTSRD-CHERI/llvm-project/) can only sensibly test libc++ using the SSH executor since we use FPGA and QEMU implementations of CHERI MIPS/RISCV.
So far I completely skipped the filesystem tests since our minimal test images don't contain python and I'm looking forward to being able to also run those tests.

My pleasure! I'm glad this is useful to others too. We're not always aware of all the different ways the test suite is used, but I keep being impressed.

I am currently in the process of merging from upstream LLVM and I will attempt to upstream my libc++ lit changes once I've completed that.
I've made a few changes to libc++'s lit remote SSH execution (e.g. adding a new SSHExecutor running with a NFS/SMBFS mounted directory to avoid the scp overhead) that might also be useful upstream.

Interesting -- please note that significant changes are coming to how we configure the libc++ test suite. Specifically, I want to decouple it from the CMake configuration so that we can start checking-in Lit configurations in the repository. It might appear a bit hand-wavy right now, however it should become clearer soon. Feel free to reach out to me on the Cpplang Slack at @ldionne if you want to chat about it.

libcxx/test/CMakeLists.txt

if (LIBCXX_CONFIGURE_IDE)
   file(GLOB_RECURSE LIBCXX_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/../include/*)
   add_executable(libcxx_test_objects EXCLUDE_FROM_ALL
           ${LIBCXX_TESTS} ${LIBCXX_TEST_HEADERS} ${LIBCXX_HEADERS})
   add_dependencies(libcxx_test_objects cxx)
 
   set(STATIC_ROOT ${LIBCXX_SOURCE_DIR}/test/std/input.output/filesystems/Inputs/static_test_env)
   add_definitions(-DLIBCXX_FILESYSTEM_STATIC_TEST_ROOT="${STATIC_ROOT}")
 
-  set(DYNAMIC_HELPER "python ${LIBCXX_SOURCE_DIR}/test/support/filesystem_dynamic_test_helper.py ")
-  add_definitions(-DLIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER="${DYNAMIC_HELPER}")
-
   split_list(LIBCXX_COMPILE_FLAGS)
   split_list(LIBCXX_LINK_FLAGS)
 
   set_target_properties(libcxx_test_objects
           PROPERTIES
             COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
             LINK_FLAGS "${LIBCXX_LINK_FLAGS}"
             EXCLUDE_FROM_ALL ON
   )
 endif()

libcxx/test/std/input.output/filesystems/lit.local.cfg

 import os
 import sys
 
 # Disable all of the filesystem tests if the dylib under test doesn't support them.
 if 'dylib-has-no-filesystem' in config.available_features:
   config.unsupported = True
 if 'c++filesystem-disabled' in config.available_features:
   config.unsupported = True
 
 inputs = os.path.join(os.path.dirname(__file__), 'Inputs', 'static_test_env')
 config.test_format.addCompileFlags(config, '-DLIBCXX_FILESYSTEM_STATIC_TEST_ROOT={}'.format(inputs))
-
-dynamic_helper = os.path.join(config.test_source_root, 'support', 'filesystem_dynamic_test_helper.py')
-assert os.path.isfile(dynamic_helper)
-config.test_format.addCompileFlags(config, '-DLIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER="{} {}"'.format(sys.executable, dynamic_helper))

libcxx/test/support/filesystem_dynamic_test_helper.py

-import sys
-import os
-import socket
-import stat
-
-# Ensure that this is being run on a specific platform
-assert sys.platform.startswith('linux') or sys.platform.startswith('darwin') \
-    or sys.platform.startswith('cygwin') or sys.platform.startswith('freebsd') \
-    or sys.platform.startswith('netbsd')
-
-test_root = None
-
-# Make sure we don't try and write outside of the test root.
-# All paths used should be sanitized
-def sanitize(p):
-    assert os.path.isdir(test_root)
-    p = os.path.realpath(p)
-    if os.path.commonprefix([test_root, p]):
-        return p
-    assert False
-
-"""
-Some of the tests restrict permissions to induce failures.
-Before we delete the test environment, we have to walk it and re-raise the
-permissions.
-"""
-def clean_recursive(root_p):
-    if not os.path.islink(root_p):
-        os.chmod(root_p, 0o777)
-    for ent in os.listdir(root_p):
-        p = os.path.join(root_p, ent)
-        if os.path.islink(p) or not os.path.isdir(p):
-            os.remove(p)
-        else:
-            assert os.path.isdir(p)
-            clean_recursive(p)
-            os.rmdir(p)
-
-
-def init_test_directory(root_p):
-    root_p = os.path.realpath(root_p)
-    assert not os.path.exists(root_p)
-    os.makedirs(root_p)
-
-
-def destroy_test_directory(root_p):
-    root_p = sanitize(root_p)
-    clean_recursive(root_p)
-    os.rmdir(root_p)
-
-
-def create_file(fname, size):
-    with open(sanitize(fname), 'w') as f:
-        f.write('c' * size)
-
-
-def create_dir(dname):
-    os.mkdir(sanitize(dname))
-
-
-def create_symlink(source, link):
-    os.symlink(sanitize(source), sanitize(link))
-
-
-def create_hardlink(source, link):
-    os.link(sanitize(source), sanitize(link))
-
-
-def create_fifo(source):
-    os.mkfifo(sanitize(source))
-
-
-def create_socket(source):
-    sock = socket.socket(socket.AF_UNIX)
-    sanitized_source = sanitize(source)
-    # AF_UNIX sockets may have very limited path length, so split it
-    # into chdir call (with technically unlimited length) followed
-    # by bind() relative to the directory
-    os.chdir(os.path.dirname(sanitized_source))
-    sock.bind(os.path.basename(sanitized_source))
-
-
-if __name__ == '__main__':
-    test_root = os.path.realpath(sys.argv[1])
-    command = " ".join(sys.argv[2:])
-    eval(command)
-    sys.exit(0)

libcxx/test/support/filesystem_test_helper.h

 #include <chrono>
 #include <vector>
 #include <regex>
 
 #include "test_macros.h"
 #include "rapid-cxx-test.h"
 #include "format_string.h"
 
+// For creating socket files
+#if !defined(__FreeBSD__) && !defined(__APPLE__)
+# include <sys/socket.h>
+# include <sys/un.h>
+#endif
+
 // static test helpers
 
 #ifndef LIBCXX_FILESYSTEM_STATIC_TEST_ROOT
 #warning "STATIC TESTS DISABLED"
 #else // LIBCXX_FILESYSTEM_STATIC_TEST_ROOT
 
 namespace StaticEnv {
 
static const fs::path RecDirFollowSymlinksIterationList[] = {
     makePath("dir1/dir2/symlink_to_dir3"),
     makePath("dir1/dir2/symlink_to_dir3/file5"),
 };
 
 } // namespace StaticEnv
 
 #endif // LIBCXX_FILESYSTEM_STATIC_TEST_ROOT
 
-
-#ifndef LIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER
-#error LIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER must be defined
-#endif
-
 namespace random_utils {
 inline char to_hex(int ch) {
   return ch < 10 ? static_cast<char>('0' + ch)
                  : static_cast<char>('a' + (ch - 10));
 }
 
 inline char random_hex_char() {
   static std::mt19937 rd{std::random_device{}()};
   static std::uniform_int_distribution<int> mrand{0, 15};
   return to_hex(mrand(rd));
 }
 
 } // namespace random_utils
 
 struct scoped_test_env
 {
-    scoped_test_env() : test_root(random_path())
-    {
-        fs_helper_run(fs_make_cmd("init_test_directory", test_root));
+    scoped_test_env() : test_root(random_path()) {
+        std::string cmd = "mkdir -p " + test_root.native();
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
 
         // Ensure that the root_path is fully resolved, i.e. it contains no
         // symlinks. The filesystem tests depend on that. We do this after
         // creating the root_path, because `fs::canonical` requires the
         // path to exist.
         test_root = fs::canonical(test_root);
     }
 
-    ~scoped_test_env()
-        { fs_helper_run(fs_make_cmd("destroy_test_directory", test_root)); }
+    ~scoped_test_env() {
+        std::string cmd = "chmod -R 777 " + test_root.native();
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
+
+        cmd = "rm -r " + test_root.native();
+        ret = std::system(cmd.c_str());
+        assert(ret == 0);
+    }
 
     scoped_test_env(scoped_test_env const &) = delete;
     scoped_test_env & operator=(scoped_test_env const &) = delete;
 
     fs::path make_env_path(std::string p) { return sanitize_path(p); }
 
     std::string sanitize_path(std::string raw) {
         assert(raw.find("..") == std::string::npos);
#endif
         }
 
         fclose(file);
         return filename;
     }
 
     std::string create_dir(std::string filename) {
         filename = sanitize_path(std::move(filename));
-        fs_helper_run(fs_make_cmd("create_dir", filename));
+        std::string cmd = "mkdir " + filename;
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
         return filename;
     }
 
     std::string create_symlink(std::string source, std::string to) {
         source = sanitize_path(std::move(source));
         to = sanitize_path(std::move(to));
-        fs_helper_run(fs_make_cmd("create_symlink", source, to));
+        std::string cmd = "ln -s " + source + ' ' + to;
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
         return to;
     }
 
     std::string create_hardlink(std::string source, std::string to) {
         source = sanitize_path(std::move(source));
         to = sanitize_path(std::move(to));
-        fs_helper_run(fs_make_cmd("create_hardlink", source, to));
+        std::string cmd = "ln " + source + ' ' + to;
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
         return to;
     }
 
     std::string create_fifo(std::string file) {
         file = sanitize_path(std::move(file));
-        fs_helper_run(fs_make_cmd("create_fifo", file));
+        std::string cmd = "mkfifo " + file;
+        int ret = std::system(cmd.c_str());
+        assert(ret == 0);
         return file;
     }
 
   // OS X and FreeBSD doesn't support socket files so we shouldn't even
   // allow tests to call this unguarded.
 #if !defined(__FreeBSD__) && !defined(__APPLE__)
     std::string create_socket(std::string file) {
         file = sanitize_path(std::move(file));
-        fs_helper_run(fs_make_cmd("create_socket", file));
+
+        ::sockaddr_un address;
+        address.sun_family = AF_UNIX;
+        assert(file.size() <= sizeof(address.sun_path));
+        ::strncpy(address.sun_path, file.c_str(), sizeof(address.sun_path));
+        int fd = ::socket(AF_UNIX, SOCK_STREAM, 0);
+        ::bind(fd, reinterpret_cast<::sockaddr*>(&address), sizeof(address));
         return file;
     }
 #endif
 
     fs::path test_root;
 
 private:
     static std::string unique_path_suffix() {
         std::string model = "test.%%%%%%";
         for (auto & ch :  model) {
           if (ch == '%')
             ch = random_utils::random_hex_char();
         }
         return model;
     }
 
     // This could potentially introduce a filesystem race with other tests
     // running at the same time, but oh well, it's just test code.
     static inline fs::path random_path() {
         fs::path tmp = fs::temp_directory_path();
         fs::path p = fs::path(tmp) / unique_path_suffix();
         return p;
     }
-
-    static inline std::string make_arg(std::string const& arg) {
-        return "'" + arg + "'";
-    }
-
-    static inline std::string make_arg(std::size_t arg) {
-        return std::to_string(arg);
-    }
-
-    template <class T>
-    static inline std::string
-    fs_make_cmd(std::string const& cmd_name, T const& arg) {
-        return cmd_name + "(" + make_arg(arg) + ")";
-    }
-
-    template <class T, class U>
-    static inline std::string
-    fs_make_cmd(std::string const& cmd_name, T const& arg1, U const& arg2) {
-        return cmd_name + "(" + make_arg(arg1) + ", " + make_arg(arg2) + ")";
-    }
-
-    void fs_helper_run(std::string const& raw_cmd) {
-        std::string cmd = LIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER;
-        cmd += " \"" + test_root.native() + "\"";
-        cmd += " \"" + raw_cmd + "\"";
-        int ret = std::system(cmd.c_str());
-        assert(ret == 0);
-    }
 };
 
 // Misc test types
 
 #define MKSTR(Str) {Str, TEST_CONCAT(L, Str), TEST_CONCAT(u, Str), TEST_CONCAT(U, Str)}
 
 struct MultiStringType {
   const char* s;