From 15ec3340c9870879f74ed72b3ab0e6fd78e58154 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Mon, 10 Feb 2025 21:44:08 +0000
Subject: [PATCH] Codechange: Compile fmt internals in a separate translation
 unit

Instead of defining FMT_HEADER_ONLY to include fmt internals
in the headers included by all fmt-using translation units.
---
 CMakeLists.txt                  |  1 +
 src/3rdparty/fmt/CMakeLists.txt |  1 +
 src/3rdparty/fmt/format.cc      | 43 +++++++++++++++++++++++++++++++++
 src/settingsgen/CMakeLists.txt  |  1 +
 src/stdafx.h                    |  3 ---
 src/strgen/CMakeLists.txt       |  1 +
 6 files changed, 47 insertions(+), 3 deletions(-)
 create mode 100644 src/3rdparty/fmt/format.cc

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6dd5d9d172..a7c0535e0d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -260,6 +260,7 @@ target_precompile_headers(openttd_lib
     src/stdafx.h
     src/core/format.hpp
 )
+set_source_files_properties(src/3rdparty/fmt/format.cc PROPERTIES SKIP_PRECOMPILE_HEADERS ON)
 
 add_subdirectory(${CMAKE_SOURCE_DIR}/bin)
 add_subdirectory(${CMAKE_SOURCE_DIR}/src)
diff --git a/src/3rdparty/fmt/CMakeLists.txt b/src/3rdparty/fmt/CMakeLists.txt
index e687b2b3d8..edc97e1fa3 100644
--- a/src/3rdparty/fmt/CMakeLists.txt
+++ b/src/3rdparty/fmt/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_files(
     chrono.h
     core.h
+    format.cc
     format.h
     format-inl.h
     ostream.h
diff --git a/src/3rdparty/fmt/format.cc b/src/3rdparty/fmt/format.cc
new file mode 100644
index 0000000000..d503fe1133
--- /dev/null
+++ b/src/3rdparty/fmt/format.cc
@@ -0,0 +1,43 @@
+// Formatting library for C++
+//
+// Copyright (c) 2012 - 2016, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#include "format-inl.h"
+
+FMT_BEGIN_NAMESPACE
+namespace detail {
+
+template FMT_API auto dragonbox::to_decimal(float x) noexcept
+    -> dragonbox::decimal_fp<float>;
+template FMT_API auto dragonbox::to_decimal(double x) noexcept
+    -> dragonbox::decimal_fp<double>;
+
+#ifndef FMT_STATIC_THOUSANDS_SEPARATOR
+template FMT_API locale_ref::locale_ref(const std::locale& loc);
+template FMT_API auto locale_ref::get<std::locale>() const -> std::locale;
+#endif
+
+// Explicit instantiations for char.
+
+template FMT_API auto thousands_sep_impl(locale_ref)
+    -> thousands_sep_result<char>;
+template FMT_API auto decimal_point_impl(locale_ref) -> char;
+
+template FMT_API void buffer<char>::append(const char*, const char*);
+
+template FMT_API void vformat_to(buffer<char>&, string_view,
+                                 typename vformat_args<>::type, locale_ref);
+
+// Explicit instantiations for wchar_t.
+
+template FMT_API auto thousands_sep_impl(locale_ref)
+    -> thousands_sep_result<wchar_t>;
+template FMT_API auto decimal_point_impl(locale_ref) -> wchar_t;
+
+template FMT_API void buffer<wchar_t>::append(const wchar_t*, const wchar_t*);
+
+}  // namespace detail
+FMT_END_NAMESPACE
diff --git a/src/settingsgen/CMakeLists.txt b/src/settingsgen/CMakeLists.txt
index 91c8eca7c8..9e71393ed6 100644
--- a/src/settingsgen/CMakeLists.txt
+++ b/src/settingsgen/CMakeLists.txt
@@ -5,6 +5,7 @@ if (NOT HOST_BINARY_DIR)
 
     set(sourcefiles
             settingsgen.cpp
+            ../3rdparty/fmt/format.cc
             ../core/alloc_func.cpp
             ../misc/getoptdata.cpp
             ../error.cpp
diff --git a/src/stdafx.h b/src/stdafx.h
index bdfc049cb6..b689aeeb57 100644
--- a/src/stdafx.h
+++ b/src/stdafx.h
@@ -298,9 +298,6 @@ char (&ArraySizeHelper(T (&array)[N]))[N];
 #	define GNU_TARGET(x)
 #endif /* __GNUC__ || __clang__ */
 
-/* For the FMT library we only want to use the headers, not link to some library. */
-#define FMT_HEADER_ONLY
-
 [[noreturn]] void NOT_REACHED(const std::source_location location = std::source_location::current());
 [[noreturn]] void AssertFailedError(const char *expression, const std::source_location location = std::source_location::current());
 
diff --git a/src/strgen/CMakeLists.txt b/src/strgen/CMakeLists.txt
index 554a9db20a..40aff5556d 100644
--- a/src/strgen/CMakeLists.txt
+++ b/src/strgen/CMakeLists.txt
@@ -8,6 +8,7 @@ if (NOT HOST_BINARY_DIR)
     set(sourcefiles
             strgen.cpp
             strgen_base.cpp
+            ../3rdparty/fmt/format.cc
             ../core/alloc_func.cpp
             ../misc/getoptdata.cpp
             ../error.cpp