gcem: new package

GCE-Math (Generalized Constant Expression Math) is a templated C++
library enabling compile-time computation of mathematical functions.
It is a header-only library, so this package is BUILDONLY:=1; the
headers and CMake config files land in staging_dir for consumers to
pick up via find_package(GCEM).

Needed as a build dependency for fluidsynth >= 2.5, whose upstream
build expects gcem at configure time and (absent a system copy)
falls back to a CMake-time download from GitHub - which breaks in
offline / restricted-network build environments such as the OpenWrt
CI.

Pinned to commit 012ae73c (2024-04-28), the revision referenced by
fluidsynth 2.5.x's bundled FindGCEM.cmake / git submodule.

CMAKE_POLICY_VERSION_MINIMUM=3.5 is set because upstream's
CMakeLists.txt declares cmake_minimum_required(VERSION 3.1), which
trips current CMake's deprecated-policy guard.

Link: https://github.com/kthohr/gcem
Signed-off-by: Daniel Golle <redacted>

diff --git a/libs/gcem/Makefile b/libs/gcem/Makefile
new file mode 100644 (file)
index 0000000..d143cf6
--- /dev/null
+++ b/libs/gcem/Makefile
@@ -0,0 +1,55 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=gcem
+PKG_RELEASE:=1
+
+# gcem upstream tags only sporadically; pin to the commit that fluidsynth
+# 2.5.x's FindGCEM.cmake / submodule references. Update in lockstep with
+# the consumer's expected revision.
+PKG_SOURCE_PROTO:=git
+PKG_SOURCE_URL:=https://github.com/kthohr/gcem.git
+PKG_SOURCE_DATE:=2024-04-28
+PKG_SOURCE_VERSION:=012ae73c6d0a2cb09ffe86475f5c6fba3926e200
+PKG_MIRROR_HASH:=70df878c9d85281c6816c231cbb320a9eccb4fb73ef32612cf8948b17716fc49
+
+PKG_MAINTAINER:=Daniel Golle <daniel@makrotopia.org>
+PKG_LICENSE:=Apache-2.0
+PKG_LICENSE_FILES:=LICENSE
+
+CMAKE_INSTALL:=1
+
+include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/cmake.mk
+
+# upstream CMakeLists.txt declares cmake_minimum_required(VERSION 3.1),
+# which trips modern CMake's deprecated-policy guard.
+CMAKE_OPTIONS += \
+       -DCMAKE_POLICY_VERSION_MINIMUM=3.5
+
+define Package/gcem
+  SECTION:=libs
+  CATEGORY:=Libraries
+  TITLE:=GCE-Math header-only constexpr math library
+  URL:=https://github.com/kthohr/gcem
+  BUILDONLY:=1
+endef
+
+define Package/gcem/description
+GCE-Math (Generalized Constant Expression Math) is a templated C++
+library enabling compile-time computation of mathematical functions.
+Header-only; consumed at build time only.
+endef
+
+define Build/InstallDev
+       $(INSTALL_DIR) $(1)/usr/include
+       $(CP) $(PKG_INSTALL_DIR)/usr/include/gcem.hpp $(1)/usr/include/
+       $(CP) $(PKG_INSTALL_DIR)/usr/include/gcem_incl $(1)/usr/include/
+       $(INSTALL_DIR) $(1)/usr/lib/cmake/gcem
+       $(CP) $(PKG_INSTALL_DIR)/usr/lib/cmake/gcem/* $(1)/usr/lib/cmake/gcem/
+endef
+
+define Package/gcem/install
+       :
+endef
+
+$(eval $(call BuildPackage,gcem))