Use fmt6 because the project can't be built with fmt8 currently

flake.nix

@@ -41,7 +41,7 @@
             ]);
             nativeBuildInputs = [
               cmake
-              fmt_8
+              (pkgs.callPackage ./fmt.nix {}).fmt_6
               protobuf
               c-ares
               boost177

fmt.diff

@@ -0,0 +1,39 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 5f0fff01..07ed8faa 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -226,16 +226,6 @@ if (FMT_SAFE_DURATION_CAST)
+   target_compile_definitions(fmt PUBLIC FMT_SAFE_DURATION_CAST)
+ endif()
+
+-add_library(fmt-header-only INTERFACE)
+-add_library(fmt::fmt-header-only ALIAS fmt-header-only)
+-
+-target_compile_definitions(fmt-header-only INTERFACE FMT_HEADER_ONLY=1)
+-target_compile_features(fmt-header-only INTERFACE ${FMT_REQUIRED_FEATURES})
+-
+-target_include_directories(fmt-header-only INTERFACE
+-  $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
+-  $<INSTALL_INTERFACE:${FMT_INC_DIR}>)
+-
+ # Install targets.
+ if (FMT_INSTALL)
+   include(CMakePackageConfigHelpers)
+@@ -273,7 +263,7 @@ if (FMT_INSTALL)
+     ${project_config}
+     INSTALL_DESTINATION ${FMT_CMAKE_DIR})
+
+-  set(INSTALL_TARGETS fmt fmt-header-only)
++  set(INSTALL_TARGETS fmt)
+   # Use a namespace because CMake provides better diagnostics for namespaced
+   # imported targets.
+   export(TARGETS ${INSTALL_TARGETS} NAMESPACE fmt::
+@@ -292,8 +282,6 @@ if (FMT_INSTALL)
+           ARCHIVE DESTINATION ${FMT_LIB_DIR}
+           RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
+
+-  install(FILES $<TARGET_PDB_FILE:${INSTALL_TARGETS}>
+-          DESTINATION ${FMT_LIB_DIR} OPTIONAL)
+   install(FILES ${FMT_HEADERS} DESTINATION "${FMT_INC_DIR}/fmt")
+   install(FILES "${pkgconfig}" DESTINATION "${FMT_PKGCONFIG_DIR}")
+ endif ()

fmt.nix

@@ -0,0 +1,98 @@
+{ lib
+, stdenv
+, fetchFromGitHub, fetchpatch
+, cmake
+, enableShared ? !stdenv.hostPlatform.isStatic
+# tests
+, mpd
+, openimageio
+, fcitx5
+, spdlog
+}:
+
+let
+  generic = { version, sha256, patches ? [ ] }:
+    stdenv.mkDerivation {
+      pname = "fmt";
+      inherit version;
+
+      outputs = [ "out" "dev" ];
+
+      src = fetchFromGitHub {
+        owner = "fmtlib";
+        repo = "fmt";
+        rev = version;
+        inherit sha256;
+      };
+      patches = [
+        # Fix BC break breaking Kodi
+        # https://github.com/xbmc/xbmc/issues/17629
+        # https://github.com/fmtlib/fmt/issues/1620
+        (fetchpatch {
+          url = "https://github.com/fmtlib/fmt/commit/7d01859ef16e6b65bc023ad8bebfedecb088bf81.patch";
+          sha256 = "0v8hm5958ih1bmnjr16fsbcmdnq4ykyf6b0hg6dxd5hxd126vnxx";
+        })
+
+        # Fix paths in pkg-config file
+        # https://github.com/fmtlib/fmt/pull/1657
+        (fetchpatch {
+          url = "https://github.com/fmtlib/fmt/commit/78f041ab5b40a1145ba686aeb8013e8788b08cd2.patch";
+          sha256 = "1hqp96zl9l3qyvsm7pxl6ah8c26z035q2mz2pqhqa0wvzd1klcc6";
+        })
+
+        # Fix cmake config paths.
+        (fetchpatch {
+          url = "https://github.com/fmtlib/fmt/pull/1702.patch";
+          sha256 = "18cadqi7nac37ymaz3ykxjqs46rvki396g6qkqwp4k00cmic23y3";
+        })
+        ./fmt.diff
+      ];
+
+
+      nativeBuildInputs = [ cmake ];
+
+      cmakeFlags = [
+        "-DBUILD_SHARED_LIBS=${if enableShared then "ON" else "OFF"}"
+      ];
+
+      doCheck = true;
+
+      passthru.tests = {
+        inherit mpd openimageio fcitx5 spdlog;
+      };
+
+      meta = with lib; {
+        description = "Small, safe and fast formatting library";
+        longDescription = ''
+          fmt (formerly cppformat) is an open-source formatting library. It can be
+          used as a fast and safe alternative to printf and IOStreams.
+        '';
+        homepage = "https://fmt.dev/";
+        changelog = "https://github.com/fmtlib/fmt/blob/${version}/ChangeLog.rst";
+        downloadPage = "https://github.com/fmtlib/fmt/";
+        maintainers = [ maintainers.jdehaas ];
+        license = licenses.mit;
+        platforms = platforms.all;
+      };
+    };
+in
+{
+  fmt_6 = generic {
+    version = "6.2.1";
+    sha256 = "sha256-LGKMl65YGbOdMuGmvVpG+mA8efyD+a5HLqAR/FV31sQ=";
+  };
+  fmt_8 = generic {
+    version = "8.1.1";
+    sha256 = "sha256-leb2800CwdZMJRWF5b1Y9ocK0jXpOX/nwo95icDf308=";
+  };
+
+  fmt_9 = generic {
+    version = "9.1.0";
+    sha256 = "sha256-rP6ymyRc7LnKxUXwPpzhHOQvpJkpnRFOt2ctvUNlYI0=";
+  };
+
+  fmt_10 = generic {
+    version = "10.1.1";
+    sha256 = "sha256-H9+1lEaHM12nzXSmo9m8S6527t+97e6necayyjCPm1A=";
+  };
+}