Merge bitcoin#24338: util: Work around libstdc++ create_directories issue

b223c3c test: Add functional test for symlinked blocks directory (laanwj)
ddb75c2 test: Add fs_tests/create_directories unit test (Hennadii Stepanov)
1f46b6e util: Work around libstdc++ create_directories issue (laanwj)

Pull request description:

  Work around libstdc++ issue [PR101510] with create_directories where the leaf already exists as a symlink. Fixes bitcoin#24257, introduced by the switch to `std::filesystem`. It is meant to be more thorough than bitcoin#24266, which worked around one instance of the problem.

  The issue was [fixed upstream](https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=124eaa50e0a34f5f89572c1aa812c50979da58fc), but unfortunately we'll have to carry a fix for it for a while.

  This introduces a function `fs::create_directories` which wraps
  `std::filesystem::create_directories`. This allows easiliy reverting the
  workaround when it is no longer necessary.

ACKs for top commit:
  jonatack:
    re-ACK b223c3c per `git range-diff df08250 67019cd b223c3c`
  hebasto:
    re-ACK b223c3c
  w0xlt:
    re-ACK b223c3c
  vasild:
    ACK b223c3c

Tree-SHA512: 028321717c8b10d16185c3711b35da6b05fb7aa31cee1c8c7e754e92bf5a0b02719a3785cd0f6f8bf052b3bd759f644af212320672baabc9e44e0b93ba464abc

Author: fanquake

src/fs.h

@@ -140,6 +140,28 @@ static inline path PathFromString(const std::string& string)
     return std::filesystem::path(string);
 #endif
 }
+
+/**
+ * Create directory (and if necessary its parents), unless the leaf directory
+ * already exists or is a symlink to an existing directory.
+ * This is a temporary workaround for an issue in libstdc++ that has been fixed
+ * upstream [PR101510].
+ */
+static inline bool create_directories(const std::filesystem::path& p)
+{
+    if (std::filesystem::is_symlink(p) && std::filesystem::is_directory(p)) {
+        return false;
+    }
+    return std::filesystem::create_directories(p);
+}
+
+/**
+ * This variant is not used. Delete it to prevent it from accidentally working
+ * around the workaround. If it is needed, add a workaround in the same pattern
+ * as above.
+ */
+bool create_directories(const std::filesystem::path& p, std::error_code& ec) = delete;
+
 } // namespace fs
 
 /** Bridge operations to C stdio */

src/test/dbwrapper_tests.cpp

@@ -203,7 +203,7 @@ BOOST_AUTO_TEST_CASE(existing_data_no_obfuscate)
 {
     // We're going to share this fs::path between two wrappers
     fs::path ph = m_args.GetDataDirBase() / "existing_data_no_obfuscate";
-    create_directories(ph);
+    fs::create_directories(ph);
 
     // Set up a non-obfuscated wrapper to write some initial data.
     std::unique_ptr<CDBWrapper> dbw = std::make_unique<CDBWrapper>(ph, (1 << 10), false, false, false);
@@ -244,7 +244,7 @@ BOOST_AUTO_TEST_CASE(existing_data_reindex)
 {
     // We're going to share this fs::path between two wrappers
     fs::path ph = m_args.GetDataDirBase() / "existing_data_reindex";
-    create_directories(ph);
+    fs::create_directories(ph);
 
     // Set up a non-obfuscated wrapper to write some initial data.
     std::unique_ptr<CDBWrapper> dbw = std::make_unique<CDBWrapper>(ph, (1 << 10), false, false, false);

src/test/fs_tests.cpp

@@ -152,4 +152,28 @@ BOOST_AUTO_TEST_CASE(rename)
     fs::remove(path2);
 }
 
+#ifndef WIN32
+BOOST_AUTO_TEST_CASE(create_directories)
+{
+    // Test fs::create_directories workaround.
+    const fs::path tmpfolder{m_args.GetDataDirBase()};
+
+    const fs::path dir{GetUniquePath(tmpfolder)};
+    fs::create_directory(dir);
+    BOOST_CHECK(fs::exists(dir));
+    BOOST_CHECK(fs::is_directory(dir));
+    BOOST_CHECK(!fs::create_directories(dir));
+
+    const fs::path symlink{GetUniquePath(tmpfolder)};
+    fs::create_directory_symlink(dir, symlink);
+    BOOST_CHECK(fs::exists(symlink));
+    BOOST_CHECK(fs::is_symlink(symlink));
+    BOOST_CHECK(fs::is_directory(symlink));
+    BOOST_CHECK(!fs::create_directories(symlink));
+
+    fs::remove(symlink);
+    fs::remove(dir);
+}
+#endif // WIN32
+
 BOOST_AUTO_TEST_SUITE_END()

test/functional/feature_dirsymlinks.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+# Copyright (c) 2022 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test successful startup with symlinked directories.
+"""
+
+import os
+import sys
+
+from test_framework.test_framework import BitcoinTestFramework, SkipTest
+
+
+def rename_and_link(*, from_name, to_name):
+    os.rename(from_name, to_name)
+    os.symlink(to_name, from_name)
+    assert os.path.islink(from_name) and os.path.isdir(from_name)
+
+class SymlinkTest(BitcoinTestFramework):
+    def skip_test_if_missing_module(self):
+        if sys.platform == 'win32':
+            raise SkipTest("Symlinks test skipped on Windows")
+
+    def set_test_params(self):
+        self.num_nodes = 1
+
+    def run_test(self):
+        self.stop_node(0)
+
+        rename_and_link(from_name=os.path.join(self.nodes[0].datadir, self.chain, "blocks"),
+                        to_name=os.path.join(self.nodes[0].datadir, self.chain, "newblocks"))
+        rename_and_link(from_name=os.path.join(self.nodes[0].datadir, self.chain, "chainstate"),
+                        to_name=os.path.join(self.nodes[0].datadir, self.chain, "newchainstate"))
+
+        self.start_node(0)
+
+
+if __name__ == '__main__':
+    SymlinkTest().main()

test/functional/test_runner.py

@@ -321,6 +321,7 @@
     'rpc_getdescriptorinfo.py',
     'rpc_mempool_entry_fee_fields_deprecation.py',
     'rpc_help.py',
+    'feature_dirsymlinks.py',
     'feature_help.py',
     'feature_shutdown.py',
     'p2p_ibd_txrelay.py',