glslang: add pkg-config file

graphics/glslang/Portfile

@@ -6,7 +6,7 @@ PortGroup           cmake 1.1
 PortGroup           legacysupport 1.1
 
 github.setup        KhronosGroup glslang 13.0.0
-revision            2
+revision            3
 
 categories          graphics devel
 license             {BSD Permissive}
@@ -36,6 +36,15 @@ compiler.cxx_standard 2017
 legacysupport.newest_darwin_requires_legacy 18
 legacysupport.use_mp_libcxx yes
 
+# Generate a pkg-config file, so that software projects that use
+# pkg-config to locate external dependencies (e.g., Godot 4.x) are able
+# to find and link against glslang.
+#
+# This patch has also been submitted upstream, and when it gets added
+# to the glslang codebase, our patchfile can be deleted:
+# https://github.com/KhronosGroup/glslang/pull/3371
+patchfiles-append       create-pkgconfig-file.diff
+
 depends_build-append    port:python${py_ver_nodot}
 configure.python        ${prefix}/bin/python${py_ver}
 configure.args-append   -DPYTHON_EXECUTABLE:FILEPATH=${configure.python}

graphics/glslang/files/create-pkgconfig-file.diff

@@ -0,0 +1,37 @@
+--- CMakeLists.txt.orig	2023-08-23 19:24:25.000000000 -0400
++++ CMakeLists.txt	2023-10-13 18:07:29.000000000 -0400
+@@ -361,4 +361,34 @@
+         DESTINATION
+             "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
+     )
++
++    # Generate a pkg-config file, so that software projects which use
++    # pkg-config to locate dependencies can find glslang
++
++    # This template is filled-in by CMake's `configure_file(... @ONLY)`.
++    # The `@...@` are substituted by CMake's configure_file(), either
++    # from variables set in CMakeLists.txt or by CMake itself.
++    # (Based on: https://www.scivision.dev/cmake-generate-pkg-config/)
++    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc.in" [=[
++prefix="@CMAKE_INSTALL_PREFIX@"
++exec_prefix="${prefix}"
++libdir="${prefix}/lib"
++includedir="${prefix}/include"
++
++Name: @PROJECT_NAME@
++Description: official reference compiler front end for the OpenGL ES and OpenGL shading languages
++Version: @PROJECT_VERSION@
++Cflags: -I"${includedir}"
++Libs: -L"${libdir}" -l@PROJECT_NAME@
++    ]=])
++    configure_file(
++        "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc.in"
++        "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
++        @ONLY)
++    install(
++        FILES
++            "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
++        DESTINATION
++            "${CMAKE_INSTALL_LIBDIR}/pkgconfig"
++    )
+ endif()