build: Bump minimum supported GCC to g++-9

Also, update the code to use constexpr, which does not work in g++-8.

Also, drop the no longer needed build-aux/m4/l_filesystem.m4.

6 files changed, 5 insertions, 47 deletions

diff --git a/build-aux/m4/l_filesystem.m4 b/build-aux/m4/l_filesystem.m4
deleted file mode 100644
index 7e577f7ae5..0000000000
--- a/build-aux/m4/l_filesystem.m4
+++ /dev/null
@@ -1,38 +0,0 @@
-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
-
-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])
-      LIBS="$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_FAILURE([cannot figure out how to use std::filesystem])
-        ])
-    ])
-
-  AC_LANG_POP
-])
diff --git a/ci/test/00_setup_env_native_qt5.sh b/ci/test/00_setup_env_native_qt5.sh
index 956701c20a..bb10a2a2de 100755
--- a/ci/test/00_setup_env_native_qt5.sh
+++ b/ci/test/00_setup_env_native_qt5.sh
@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_native_qt5
 export CI_IMAGE_NAME_TAG="ubuntu:20.04"
-# Use minimum supported python3.8 and gcc-8 (or best-effort gcc-9), see doc/dependencies.md
+# Use minimum supported python3.8 and gcc-9, see doc/dependencies.md
 export PACKAGES="gcc-9 g++-9 python3-zmq qtbase5-dev qttools5-dev-tools libdbus-1-dev libharfbuzz-dev"
 export DEP_OPTS="NO_QT=1 NO_UPNP=1 NO_NATPMP=1 DEBUG=1 ALLOW_HOST_PACKAGES=1 CC=gcc-9 CXX=g++-9"
 export TEST_RUNNER_EXTRA="--previous-releases --coverage --extended --exclude feature_dbcrash"  # Run extended tests so that coverage does not fail, but exclude the very slow dbcrash
diff --git a/configure.ac b/configure.ac
index 8e73213c78..db1b7f758a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -115,9 +115,6 @@ else
 AX_CXX_COMPILE_STDCXX([20], [noext], [mandatory])
 fi
 
-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],[
diff --git a/doc/dependencies.md b/doc/dependencies.md
index ef60839830..4344ed259e 100644
--- a/doc/dependencies.md
+++ b/doc/dependencies.md
@@ -9,7 +9,7 @@ You can find installation instructions in the `build-*.md` file for your platfor
 | [Autoconf](https://www.gnu.org/software/autoconf/) | [2.69](https://github.com/bitcoin/bitcoin/pull/17769) |
 | [Automake](https://www.gnu.org/software/automake/) | [1.13](https://github.com/bitcoin/bitcoin/pull/18290) |
 | [Clang](https://clang.llvm.org) | [10.0](https://github.com/bitcoin/bitcoin/pull/27682) |
-| [GCC](https://gcc.gnu.org) | [8.1](https://github.com/bitcoin/bitcoin/pull/23060) |
+| [GCC](https://gcc.gnu.org) | [9.1](https://github.com/bitcoin/bitcoin/pull/27662) |
 | [Python](https://www.python.org) (scripts, tests) | [3.8](https://github.com/bitcoin/bitcoin/pull/27483) |
 | [systemtap](https://sourceware.org/systemtap/) ([tracing](tracing.md))| N/A |
 
diff --git a/src/qt/addresstablemodel.cpp b/src/qt/addresstablemodel.cpp
index 0d0f1a4d15..e4689e4389 100644
--- a/src/qt/addresstablemodel.cpp
+++ b/src/qt/addresstablemodel.cpp
@@ -53,15 +53,14 @@ struct AddressTableEntryLessThan
 };
 
 /* Determine address type from address purpose */
-static AddressTableEntry::Type translateTransactionType(wallet::AddressPurpose purpose, bool isMine)
+constexpr AddressTableEntry::Type translateTransactionType(wallet::AddressPurpose purpose, bool isMine)
 {
     // "refund" addresses aren't shown, and change addresses aren't returned by getAddresses at all.
     switch (purpose) {
     case wallet::AddressPurpose::SEND: return AddressTableEntry::Sending;
     case wallet::AddressPurpose::RECEIVE: return AddressTableEntry::Receiving;
     case wallet::AddressPurpose::REFUND: return AddressTableEntry::Hidden;
-    // No default case to allow for compiler to warn
-    }
+    } // no default case, so the compiler can warn about missing cases
     assert(false);
 }
 
diff --git a/src/txrequest.cpp b/src/txrequest.cpp
index 96a3d2eeeb..40d36132de 100644
--- a/src/txrequest.cpp
+++ b/src/txrequest.cpp
@@ -69,7 +69,7 @@ struct Announcement {
     const bool m_is_wtxid : 1;
 
     /** What state this announcement is in.
-     *  This is a uint8_t instead of a State to silence a GCC warning in versions prior to 8.4 and 9.3.
+     *  This is a uint8_t instead of a State to silence a GCC warning in versions prior to 9.3.
      *  See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61414 */
     uint8_t m_state : 3;