build: add support for std::filesystem

Add a macro to check if linking with -lstdc++fs or -lc++fs is required.

1 files changed, 47 insertions, 0 deletions

diff --git a/build-aux/m4/l_filesystem.m4 b/build-aux/m4/l_filesystem.m4
new file mode 100644
index 0000000000..ca3a0cd41c
--- /dev/null
+++ b/build-aux/m4/l_filesystem.m4
@@ -0,0 +1,47 @@
+dnl Copyright (c) 2022 The Bitcoin Core developers
+dnl Distributed under the MIT software license, see the accompanying
+dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+# GCC 8.1 and earlier requires -lstdc++fs
+# Clang 8.0.0 (libc++) and earlier requires -lc++fs
+
+m4_define([_CHECK_FILESYSTEM_testbody], [[
+  #include <filesystem>
+
+  namespace fs = std::filesystem;
+
+  int main() {
+    (void)fs::current_path().root_name();
+    return 0;
+  }
+]])
+
+AC_DEFUN([CHECK_FILESYSTEM], [
+
+  AC_LANG_PUSH(C++)
+
+  AC_MSG_CHECKING([whether std::filesystem can be used without link library])
+
+  AC_LINK_IFELSE([AC_LANG_SOURCE([_CHECK_FILESYSTEM_testbody])],[
+      AC_MSG_RESULT([yes])
+    ],[
+      AC_MSG_RESULT([no])
+      SAVED_LIBS="$LIBS"
+      LIBS="$SAVED_LIBS -lstdc++fs"
+      AC_MSG_CHECKING([whether std::filesystem needs -lstdc++fs])
+      AC_LINK_IFELSE([AC_LANG_SOURCE([_CHECK_FILESYSTEM_testbody])],[
+          AC_MSG_RESULT([yes])
+        ],[
+          AC_MSG_RESULT([no])
+          AC_MSG_CHECKING([whether std::filesystem needs -lc++fs])
+          LIBS="$SAVED_LIBS -lc++fs"
+          AC_LINK_IFELSE([AC_LANG_SOURCE([_CHECK_FILESYSTEM_testbody])],[
+            AC_MSG_RESULT([yes])
+        ],[
+            AC_MSG_FAILURE([cannot figure out how to use std::filesystem])
+          ])
+        ])
+    ])
+
+  AC_LANG_POP
+])