Simplify fs::path by dropping filename() and make_preferred() overloads

These overloads were needed to allow passing `fs::path` objects directly to
libstdc++'s `fstream` constructors, but after the previous commit, there is no
longer any remaining code that does pass `fs::path` objects to `fstream`
constructors. Writing new code which does this is also discouraged because the
standard has been updated in https://wg21.link/lwg3430 to disallow it.

Dropping these also means its no longer possible to pass `fs::path` arguments
directly to `fstream::open` in libstdc++, which is somewhat unfortunate but not
a big loss because it is already not possible to pass them to the constructor.
So this commit updates `fstream::open` calls.

Additionally, this change required updates to src/bitcoin.cpp since it was
relying on the overloaded filename() method.

src/bitcoin.cpp

@@ -209,7 +209,7 @@ static void ExecCommand(const std::vector<const char*>& args, std::string_view w
 
     // Try to resolve any symlinks and figure out the directory containing the wrapper executable.
     std::error_code ec;
-    fs::path wrapper_dir{fs::weakly_canonical(wrapper_path, ec)};
+    auto wrapper_dir{fs::weakly_canonical(wrapper_path, ec)};
     if (wrapper_dir.empty()) wrapper_dir = wrapper_path; // Restore previous path if weakly_canonical failed.
     wrapper_dir = wrapper_dir.parent_path();
 
@@ -225,7 +225,7 @@ static void ExecCommand(const std::vector<const char*>& args, std::string_view w
 
     // If wrapper is installed in a bin/ directory, look for target executable
     // in libexec/
-    (wrapper_dir.filename() == "bin" && try_exec(fs::path{wrapper_dir.parent_path()} / "libexec" / arg0.filename())) ||
+    (wrapper_dir.filename() == "bin" && try_exec(wrapper_dir.parent_path() / "libexec" / arg0.filename())) ||
 #ifdef WIN32
     // Otherwise check the "daemon" subdirectory in a windows install.
     (!wrapper_dir.empty() && try_exec(wrapper_dir / "daemon" / arg0.filename())) ||

src/common/settings.cpp

@@ -78,7 +78,7 @@ bool ReadSettings(const fs::path& path, std::map<std::string, SettingsValue>& va
     if (!fs::exists(path)) return true;
 
     std::ifstream file;
-    file.open(path);
+    file.open(path.std_path());
     if (!file.is_open()) {
       errors.emplace_back(strprintf("%s. Please check permissions.", fs::PathToString(path)));
       return false;
@@ -133,7 +133,7 @@ bool WriteSettings(const fs::path& path,
         out.pushKVEnd(value.first, value.second);
     }
     std::ofstream file;
-    file.open(path);
+    file.open(path.std_path());
     if (file.fail()) {
         errors.emplace_back(strprintf("Error: Unable to open settings file %s for writing", fs::PathToString(path)));
         return false;

src/rpc/request.cpp

@@ -114,7 +114,7 @@ GenerateAuthCookieResult GenerateAuthCookie(const std::optional<fs::perms>& cook
     if (filepath_tmp.empty()) {
         return GenerateAuthCookieResult::DISABLED; // -norpccookiefile
     }
-    file.open(filepath_tmp);
+    file.open(filepath_tmp.std_path());
     if (!file.is_open()) {
         LogWarning("Unable to open cookie authentication file %s for writing", fs::PathToString(filepath_tmp));
         return GenerateAuthCookieResult::ERR;
@@ -153,7 +153,7 @@ bool GetAuthCookie(std::string *cookie_out)
     if (filepath.empty()) {
         return true; // -norpccookiefile
     }
-    file.open(filepath);
+    file.open(filepath.std_path());
     if (!file.is_open())
         return false;
     std::getline(file, cookie);

src/test/settings_tests.cpp

@@ -45,7 +45,7 @@ inline std::ostream& operator<<(std::ostream& os, const std::pair<std::string, c
 inline void WriteText(const fs::path& path, const std::string& text)
 {
     std::ofstream file;
-    file.open(path);
+    file.open(path.std_path());
     file << text;
 }
 

src/util/fs.h

@@ -75,11 +75,6 @@ public:
         const std::u8string& utf8_str{std::filesystem::path::u8string()};
         return std::string{utf8_str.begin(), utf8_str.end()};
     }
-
-    // Required for path overloads in <fstream>.
-    // See https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=96e0367ead5d8dcac3bec2865582e76e2fbab190
-    path& make_preferred() { std::filesystem::path::make_preferred(); return *this; }
-    path filename() const { return std::filesystem::path::filename(); }
 };
 
 static inline path u8path(const std::string& utf8_str)

src/wallet/dump.cpp

@@ -37,7 +37,7 @@ bool DumpWallet(const ArgsManager& args, WalletDatabase& db, bilingual_str& erro
         return false;
     }
     std::ofstream dump_file;
-    dump_file.open(path);
+    dump_file.open(path.std_path());
     if (dump_file.fail()) {
         error = strprintf(_("Unable to open %s for writing"), fs::PathToString(path));
         return false;