Merge bitcoin#20744: Use std::filesystem. Remove Boost Filesystem & System

0726932 build: remove Boost::system usage (fanquake)
b87f9c5 build: remove boost::filesystem usage (Kiminuo)
41d7166 refactor: replace boost::filesystem with std::filesystem (Kiminuo)
ffc89d1 build: add support for std::filesystem (fanquake)

Pull request description:

  This PR replaces our Boost Filesystem usage with [`std::filesystem`](https://en.cppreference.com/w/cpp/filesystem) and includes dropping Boost System as a dependency. It includes a squashed down version of the changes from bitcoin#19245.

  [A macro has been added](bitcoin@7002c4a), modelling how we check for `-latomic` to facilitate linking with `-lstdc++fs` when required. This is  ~GCC < 9.1 & ~Clang < 9.0, however not always. i.e you could be using Clang 7 on top of a GCC 9 installation (i.e Ubuntu Focal) and use `<filesystem>` without passing any additional arguments. I've tested this with GCC 8 on Bionic, Clang 7 on Focal & with Apple Clang 12.0.0 on macOS.

  Guix build:
  ```bash
  bash-5.1# find guix-build-$(git rev-parse --short=12 HEAD)/output/ -type f -print0 | env LC_ALL=C sort -z | xargs -r0 sha256sum
  c1f9b326f9be4140f00cebeae5ff8de428a2fb8ecced539fcc36c53f53bfecf4  guix-build-07269321f38e/output/aarch64-linux-gnu/SHA256SUMS.part
  b44aca3bcf5ea92a3a6c48c24d6f85576f425f59b73528d4d00c20e950cf2128  guix-build-07269321f38e/output/aarch64-linux-gnu/bitcoin-07269321f38e-aarch64-linux-gnu-debug.tar.gz
  27a5553f7bd14797293fc40c5fb131c91e98a61d5481a283f13a1d0497eb5ed8  guix-build-07269321f38e/output/aarch64-linux-gnu/bitcoin-07269321f38e-aarch64-linux-gnu.tar.gz
  99e55a88823f6095864a09c9eaa824e24d9ec527380eb394f751c7205b930f69  guix-build-07269321f38e/output/arm-linux-gnueabihf/SHA256SUMS.part
  b720b2724fa47fde584f58ed3b587f1d1183523540777fd367ab7e582605cfea  guix-build-07269321f38e/output/arm-linux-gnueabihf/bitcoin-07269321f38e-arm-linux-gnueabihf-debug.tar.gz
  c19c247f4e9e0d7f888ac8ba9de1c12d382f48fa828a685d4fe02818a18abd1f  guix-build-07269321f38e/output/arm-linux-gnueabihf/bitcoin-07269321f38e-arm-linux-gnueabihf.tar.gz
  55b49ccb38de03bb95101354a16fd8d2190abede5ccc0d9b00b40c0cd526a2f6  guix-build-07269321f38e/output/arm64-apple-darwin/SHA256SUMS.part
  baa44752470a6be9acae1c2f8fd1b9bc37afb00971787ea11fbaeddc9ab7c4aa  guix-build-07269321f38e/output/arm64-apple-darwin/bitcoin-07269321f38e-arm64-apple-darwin.tar.gz
  ad7df4d8026d5bcce1321cdccc2e1820e8a8bb7e1064ed16e20a7ea354057fd2  guix-build-07269321f38e/output/arm64-apple-darwin/bitcoin-07269321f38e-osx-unsigned.dmg
  f342066dc34a14d67c47779a2413a14633a996e8e7ddca89ae0184e23ef99efd  guix-build-07269321f38e/output/arm64-apple-darwin/bitcoin-07269321f38e-osx-unsigned.tar.gz
  f6905346a5d48f57805fb062d0247ab5007c89047070a0b3125941dd1a2b8aa6  guix-build-07269321f38e/output/dist-archive/bitcoin-07269321f38e.tar.gz
  a1f6c4b2b118dbd89770801f0bcffd2218b82df408cd227e34c40493469bb7a2  guix-build-07269321f38e/output/powerpc64-linux-gnu/SHA256SUMS.part
  ba8359426e523bf013d93579c1bedc57380214c8170a9743b64ec1a8a3bbccbf  guix-build-07269321f38e/output/powerpc64-linux-gnu/bitcoin-07269321f38e-powerpc64-linux-gnu-debug.tar.gz
  b0bb500c274a683ea28ecbc1e8f18c618a9f8acb00045f80ae43c515288402c0  guix-build-07269321f38e/output/powerpc64-linux-gnu/bitcoin-07269321f38e-powerpc64-linux-gnu.tar.gz
  38c85e9589e092cd3aa08996aa383c0ccd5c73208943389741355a6eb7f72537  guix-build-07269321f38e/output/powerpc64le-linux-gnu/SHA256SUMS.part
  50fcba7942ff48d91e84c093fda0affc17e46167fe1d5137c6e14c5c41f289d1  guix-build-07269321f38e/output/powerpc64le-linux-gnu/bitcoin-07269321f38e-powerpc64le-linux-gnu-debug.tar.gz
  fa08ef1ceca072e014faa95ffee945954b2976fa28f90926b87ab0e5f15f8ca5  guix-build-07269321f38e/output/powerpc64le-linux-gnu/bitcoin-07269321f38e-powerpc64le-linux-gnu.tar.gz
  e52dd80a9c306d6aeb544acaa1f4ed560b6b92b5184764a05026d45451aa2e94  guix-build-07269321f38e/output/riscv64-linux-gnu/SHA256SUMS.part
  864e0a16c485b4159cec3ee0a83b046f1b1c3bc821670011c5ac5cd09ddfb91f  guix-build-07269321f38e/output/riscv64-linux-gnu/bitcoin-07269321f38e-riscv64-linux-gnu-debug.tar.gz
  4a061172181322e7ad0cf06405bf74f4c8683eaba3a67ecfd46158cba7627f62  guix-build-07269321f38e/output/riscv64-linux-gnu/bitcoin-07269321f38e-riscv64-linux-gnu.tar.gz
  876d82251853205420dffe7237523fc6ee3d09f78bf74cc03dc71f548446f335  guix-build-07269321f38e/output/x86_64-apple-darwin/SHA256SUMS.part
  3f82b2e62c60eee68e7b8fc28e4792e069e3c2cd780ee2d67290ca422cdbc47c  guix-build-07269321f38e/output/x86_64-apple-darwin/bitcoin-07269321f38e-osx-unsigned.dmg
  4ccdd4c410cac9d627e54ce83ee4816608681735da3cb93c60c5eb70ca86337a  guix-build-07269321f38e/output/x86_64-apple-darwin/bitcoin-07269321f38e-osx-unsigned.tar.gz
  2179d36b2f60e28c15262d4e51f27465b5ae077f60e550345e125683ca611066  guix-build-07269321f38e/output/x86_64-apple-darwin/bitcoin-07269321f38e-osx64.tar.gz
  b377e72fe84b6a982b8d414d60c85e6319523dff50dc852a0ba907f6d850ddd0  guix-build-07269321f38e/output/x86_64-linux-gnu/SHA256SUMS.part
  8547e2f582ce05ae6a6224793b64efb2eb63f2816bf0bed5d53fcc4786274597  guix-build-07269321f38e/output/x86_64-linux-gnu/bitcoin-07269321f38e-x86_64-linux-gnu-debug.tar.gz
  83b64805aa39f31a6fa4c2ed41e029c3be084e6dea06b90fac1ebca5c95bce29  guix-build-07269321f38e/output/x86_64-linux-gnu/bitcoin-07269321f38e-x86_64-linux-gnu.tar.gz
  ```

ACKs for top commit:
  laanwj:
    Code review ACK 0726932
  MarcoFalke:
    Concept ACK 0726932 🎀
  hebasto:
    ACK 0726932

Tree-SHA512: 1f11614467d2013ed799f23c1c14716570f4c798f231671c731a69c7773ef32a0aa2acc69d4ac2f1f176ef6f160f56566c6bd75c9c059a0e82ab4c58d2b2a750

Author: MarcoFalke

build-aux/m4/ax_boost_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
+])

build-aux/m4/ax_boost_system.m4

@@ -44,15 +44,9 @@
 /* define if the Boost library is available */
 #define HAVE_BOOST /**/
 
-/* define if the Boost::Filesystem library is available */
-#define HAVE_BOOST_FILESYSTEM /**/
-
 /* define if external signer support is enabled (requires Boost::Process) */
 #define ENABLE_EXTERNAL_SIGNER /**/
 
-/* define if the Boost::System library is available */
-#define HAVE_BOOST_SYSTEM /**/
-
 /* define if the Boost::Unit_Test_Framework library is available */
 #define HAVE_BOOST_UNIT_TEST_FRAMEWORK /**/
 

build-aux/m4/l_filesystem.m4

@@ -3,7 +3,6 @@
   "version-string": "1",
   "dependencies": [
     "berkeleydb",
-    "boost-filesystem",
     "boost-multi-index",
     "boost-process",
     "boost-signals2",

build_msvc/bitcoin_config.h.in

@@ -7,7 +7,7 @@
 export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_native_asan
-export PACKAGES="clang llvm python3-zmq qtbase5-dev qttools5-dev-tools libevent-dev bsdmainutils libboost-dev libboost-system-dev libboost-filesystem-dev libboost-test-dev libdb5.3++-dev libminiupnpc-dev libnatpmp-dev libzmq3-dev libqrencode-dev libsqlite3-dev"
+export PACKAGES="clang llvm python3-zmq qtbase5-dev qttools5-dev-tools libevent-dev bsdmainutils libboost-dev libboost-test-dev libdb5.3++-dev libminiupnpc-dev libnatpmp-dev libzmq3-dev libqrencode-dev libsqlite3-dev"
 export DOCKER_NAME_TAG=ubuntu:22.04
 export NO_DEPENDS=1
 export GOAL="install"

build_msvc/vcpkg.json

@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export DOCKER_NAME_TAG="ubuntu:20.04"
 export CONTAINER_NAME=ci_native_fuzz
-export PACKAGES="clang llvm python3 libevent-dev bsdmainutils libboost-dev libboost-system-dev libboost-filesystem-dev libboost-test-dev libsqlite3-dev"
+export PACKAGES="clang llvm python3 libevent-dev bsdmainutils libboost-dev libboost-test-dev libsqlite3-dev"
 export NO_DEPENDS=1
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false

ci/test/00_setup_env_native_asan.sh

@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export DOCKER_NAME_TAG="ubuntu:20.04"
 export CONTAINER_NAME=ci_native_fuzz_valgrind
-export PACKAGES="clang llvm python3 libevent-dev bsdmainutils libboost-dev libboost-system-dev libboost-filesystem-dev libboost-test-dev libsqlite3-dev valgrind"
+export PACKAGES="clang llvm python3 libevent-dev bsdmainutils libboost-dev libboost-test-dev libsqlite3-dev valgrind"
 export NO_DEPENDS=1
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false

ci/test/00_setup_env_native_fuzz.sh

@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export DOCKER_NAME_TAG="ubuntu:20.04"
 export CONTAINER_NAME=ci_native_valgrind
-export PACKAGES="valgrind clang llvm python3-zmq libevent-dev bsdmainutils libboost-dev libboost-system-dev libboost-filesystem-dev libboost-test-dev libdb5.3++-dev libminiupnpc-dev libnatpmp-dev libzmq3-dev libsqlite3-dev"
+export PACKAGES="valgrind clang llvm python3-zmq libevent-dev bsdmainutils libboost-dev libboost-test-dev libdb5.3++-dev libminiupnpc-dev libnatpmp-dev libzmq3-dev libsqlite3-dev"
 export USE_VALGRIND=1
 export NO_DEPENDS=1
 export TEST_RUNNER_EXTRA="--nosandbox --exclude rpc_bind,feature_bind_extra"  # Excluded for now, see https://github.com/bitcoin/bitcoin/issues/17765#issuecomment-602068547

ci/test/00_setup_env_native_fuzz_with_valgrind.sh

@@ -83,6 +83,9 @@ AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 dnl Check if -latomic is required for <std::atomic>
 CHECK_ATOMIC
 
+dnl check if additional link flags are required for std::filesystem
+CHECK_FILESYSTEM
+
 dnl Unless the user specified OBJCXX, force it to be the same as CXX. This ensures
 dnl that we get the same -std flags for both.
 m4_ifdef([AC_PROG_OBJCXX],[
@@ -1404,14 +1407,12 @@ if test "$use_boost" = "yes"; then
   if test "$want_boost" = "no"; then
     AC_MSG_ERROR([only libbitcoinconsensus can be built without Boost])
   fi
-  AX_BOOST_SYSTEM
-  AX_BOOST_FILESYSTEM
 
   if test "$suppress_external_warnings" != "no"; then
     BOOST_CPPFLAGS=SUPPRESS_WARNINGS($BOOST_CPPFLAGS)
   fi
 
-  BOOST_LIBS="$BOOST_LDFLAGS $BOOST_SYSTEM_LIB $BOOST_FILESYSTEM_LIB"
+  BOOST_LIBS="$BOOST_LDFLAGS"
 fi
 
 if test "$use_external_signer" != "no"; then