cmake: Add Find Module to support Android and iOS consumers

This commit adds a Find Module implementing the necessary logic to link
against GStreamer, while implementing some extra bits to enhance the
compatibility.

The first addition is the `mobile` target, which implements the
monolithic `gstreamer_android` library, and which here gains
compatibility with Apple's operating systems.

The second addition is the handling of the basic GStreamer libraries as
`--whole-archive` when statically linked, which was ported from the
ndk-build project in Cerbero. This is not easy to do, as CMake suffers
from several issues that impede its proper usage of pkg-config:

- It cannot differentiate between system/compiler specific libraries
  e.g. `-lm`, `-ldl`, but especially `-framework Cocoa`.
- It does not support `--whole-archive` natively until 3.27
- It attempts to reorder flags blindly by separating them with spaces,
  thus requiring the use of `-Wl,` wrapping or (in the case of Apple
  frameworks) manual framework lookup

The third addition is the port of the Fontconfig and ca-certificates
bundling logic.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6881>

subprojects/gstreamer/cmake/FindGStreamer.cmake

@@ -0,0 +1,449 @@
+# SPDX-FileCopyrightText: 2024 L. E. Segovia <amy@centricular.com>
+# SPDX-License-Ref: LGPL-2.1-or-later
+
+#[=======================================================================[.rst:
+FindGStreamer
+-------
+
+Finds the GStreamer library. Requires ``pkg-config`` to be installed.
+
+Configuration
+^^^^^^^^^^^^^
+
+This module can be configured with the following variables:
+
+``GStreamer_STATIC``
+  Link against GStreamer statically (see below).
+
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module defines the following :prop_tgt:`IMPORTED` targets:
+
+``GStreamer::GStreamer``
+  The GStreamer library.
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This will define the following variables:
+
+``GStreamer_FOUND``
+  True if the system has the GStreamer library.
+``GStreamer_VERSION``
+  The version of the GStreamer library which was found.
+``GStreamer_INCLUDE_DIRS``
+  Include directories needed to use GStreamer.
+``GStreamer_LIBRARIES``
+  Libraries needed to link to GStreamer.
+
+Cache Variables
+^^^^^^^^^^^^^^^
+
+The following cache variables may also be set:
+
+``GStreamer_INCLUDE_DIR``
+  The directory containing ``gst/gstversion.h``.
+``GStreamer_LIBRARY``
+  The path to the GStreamer library.
+
+Configuration Variables
+^^^^^^^^^^^^^^^
+
+Setting the following variables is required, depending on the operating system:
+
+``GStreamer_ROOT_DIR``
+  Installation prefix of the GStreamer SDK.
+
+``GStreamer_USE_STATIC_LIBS`
+  Set to ON to force the use of the static libraries. Default is OFF.
+
+``GStreamer_EXTRA_DEPS``
+  pkg-config names of the extra dependencies that will be included whenever linking against GStreamer.
+
+#]=======================================================================]
+
+if (GStreamer_FOUND)
+    return()
+endif()
+
+#####################
+#  Setup variables  #
+#####################
+
+if (NOT DEFINED GStreamer_ROOT_DIR AND DEFINED GSTREAMER_ROOT)
+    set(GStreamer_ROOT_DIR ${GSTREAMER_ROOT})
+endif()
+
+if (NOT GStreamer_ROOT_DIR)
+    set(GStreamer_ROOT_DIR "${CMAKE_CURRENT_LIST_DIR}/../../")
+endif()
+
+if (NOT EXISTS "${GStreamer_ROOT_DIR}")
+    message(FATAL_ERROR "The directory GStreamer_ROOT_DIR=${GStreamer_ROOT_DIR} does not exist")
+endif()
+
+if (NOT DEFINED GStreamer_USE_STATIC_LIBS)
+set(GStreamer_USE_STATIC_LIBS OFF)
+endif()
+
+# Set the environment for pkg-config
+if (WIN32)
+    set(ENV{PKG_CONFIG_PATH} "${GStreamer_ROOT_DIR}/lib/pkgconfig;${GStreamer_ROOT_DIR}/lib/gstreamer-1.0/pkgconfig;${GStreamer_ROOT_DIR}/lib/gio/modules/pkgconfig")
+else()
+    set(ENV{PKG_CONFIG_PATH} "${GStreamer_ROOT_DIR}/lib/pkgconfig:${GStreamer_ROOT_DIR}/lib/gstreamer-1.0/pkgconfig:${GStreamer_ROOT_DIR}/lib/gio/modules/pkgconfig")
+endif()
+
+# Set the list of extra dependencies
+if (NOT DEFINED GStreamer_EXTRA_DEPS)
+    set(GStreamer_EXTRA_DEPS)
+    if (DEFINED GSTREAMER_EXTRA_DEPS)
+        set(GStreamer_EXTRA_DEPS ${GSTREAMER_EXTRA_DEPS})
+    endif()
+endif()
+
+# Find libraries. This is meant to be used with static libraries
+# (hence the reprioritization) but I've added a fallback to shared libraries
+# and stub modules in case any are non-existent.
+function(_gst_find_library LOCAL_LIB GST_LOCAL_LIB)
+    if (DEFINED ${GST_LOCAL_LIB})
+        return()
+    endif()
+
+    set(_gst_suffixes ${CMAKE_FIND_LIBRARY_SUFFIXES})
+    set(_gst_prefixes ${CMAKE_FIND_LIBRARY_PREFIXES})
+    if (APPLE)
+        set(CMAKE_FIND_LIBRARY_SUFFIXES ".a" ".dylib" ".so" ".tbd")
+        set(CMAKE_FIND_LIBRARY_PREFIXES "" "lib")
+    elseif (UNIX)
+        set(CMAKE_FIND_LIBRARY_SUFFIXES ".a" ".so")
+        set(CMAKE_FIND_LIBRARY_PREFIXES "" "lib")
+    else()
+        set(CMAKE_FIND_LIBRARY_SUFFIXES ".a" ".lib")
+        set(CMAKE_FIND_LIBRARY_PREFIXES "" "lib")
+    endif()
+
+    if ("${LOCAL_LIB}" IN_LIST _gst_IGNORED_SYSTEM_LIBRARIES)
+        set(${GST_LOCAL_LIB} ${LOCAL_LIB} PARENT_SCOPE)
+    else()
+        find_library(${GST_LOCAL_LIB}
+            ${LOCAL_LIB}
+            HINTS ${ARGN}
+            NO_DEFAULT_PATH
+            NO_CMAKE_FIND_ROOT_PATH
+            REQUIRED
+        )
+        set(${GST_LOCAL_LIB} "${${GST_LOCAL_LIB}}" PARENT_SCOPE)
+        if (NOT ${GST_LOCAL_LIB})
+            message(FATAL_ERROR "${LOCAL_LIB} was unexpectedly not found.")
+        endif()
+    endif()
+
+    set(CMAKE_FIND_LIBRARY_SUFFIXES ${_gst_suffixes})
+    set(CMAKE_FIND_LIBRARY_PREFIXES ${_gst_prefixes})
+endfunction()
+
+macro(_gst_apply_link_libraries HIDE PC_LIBRARIES PC_HINTS GST_TARGET)
+    if (APPLE AND ${HIDE})
+        target_link_directories(${GST_TARGET} INTERFACE
+            ${${PC_HINTS}}
+        )
+    endif()
+    foreach(LOCAL_LIB IN LISTS ${PC_LIBRARIES})
+        if (LOCAL_LIB MATCHES "${_gst_SRT_REGEX_PATCH}")
+            string(REGEX REPLACE "${_gst_SRT_REGEX_PATCH}" "\\1" LOCAL_LIB "${LOCAL_LIB}")
+        endif()
+        string(MAKE_C_IDENTIFIER "_gst_${LOCAL_LIB}" GST_LOCAL_LIB)
+        if (NOT ${GST_LOCAL_LIB})
+            _gst_find_library(${LOCAL_LIB} ${GST_LOCAL_LIB} ${${PC_HINTS}})
+        endif()
+        if ("${${GST_LOCAL_LIB}}" IN_LIST _gst_IGNORED_SYSTEM_LIBRARIES)
+            target_link_libraries(${GST_TARGET} INTERFACE
+                ${${GST_LOCAL_LIB}})
+        elseif (APPLE AND ${HIDE})
+            set(LOCAL_FILE)
+            get_filename_component(LOCAL_FILE ${${GST_LOCAL_LIB}} NAME)
+            target_link_libraries(${GST_TARGET} INTERFACE
+                "-hidden-l${LOCAL_FILE}")
+        elseif((UNIX OR ANDROID) AND ${HIDE})
+            target_link_libraries(${GST_TARGET} INTERFACE
+                -Wl,--exclude-libs,${${GST_LOCAL_LIB}})
+        else()
+            target_link_libraries(${GST_TARGET} INTERFACE
+                ${${GST_LOCAL_LIB}})
+        endif()
+    endforeach()
+endmacro()
+
+macro(_gst_filter_missing_directories GST_INCLUDE_DIRS)
+    set(_gst_include_dirs)
+    foreach(DIR IN LISTS ${GST_INCLUDE_DIRS})
+        if ((IS_DIRECTORY "${DIR}") AND (EXISTS "${DIR}"))
+            list(APPEND _gst_include_dirs "${DIR}")
+        else()
+            message(WARNING "Skipping missing include folder ${DIR}.")
+        endif()
+    endforeach()
+    set(${GST_INCLUDE_DIRS} "${_gst_include_dirs}")
+endmacro()
+
+macro(_gst_apply_frameworks PC_STATIC_LDFLAGS_OTHER GST_TARGET)
+    if (APPLE)
+        # LDFLAGS_OTHER may include framework linkage. Because CMake
+        # iterates over arguments separated by spaces, it doesn't realise
+        # that those arguments must not be split.
+        set(new_ldflags)
+        set(assemble_framework FALSE)
+        foreach(_arg IN LISTS ${PC_STATIC_LDFLAGS_OTHER})
+            if (assemble_framework)
+                set(assemble_framework FALSE)
+                find_library(GST_${_arg}_LIB ${_arg} REQUIRED)
+                target_link_libraries(${GST_TARGET}
+                    INTERFACE
+                        "${GST_${_arg}_LIB}"
+                )
+            elseif (_arg STREQUAL "-framework")
+                set(assemble_framework TRUE)
+            else()
+                set(assemble_framework FALSE)
+                list(APPEND new_ldflags "${_arg}")
+            endif()
+        endforeach()
+        set_target_properties(${GST_TARGET} PROPERTIES
+            INTERFACE_LINK_OPTIONS "${new_ldflags}"
+        )
+    else()
+        set_target_properties(${TARGET} PROPERTIES
+            INTERFACE_LINK_OPTIONS "${${PC_STATIC_LDFLAGS_OTHER}}"
+        )
+    endif()
+endmacro()
+
+################################
+#      Set up the targets      #
+################################
+
+find_package(PkgConfig REQUIRED)
+
+# GStreamer's pkg-config modules are a MUST -- but we'll test them below
+pkg_check_modules(PC_GStreamer gstreamer-1.0 ${GStreamer_EXTRA_DEPS})
+# Simulate the list that'll be wholearchive'd.
+# Unfortunately, this uses an option only available with pkgconf.
+# set(_old_pkg_config_executable "${PKG_CONFIG_EXECUTABLE}")
+# set(PKG_CONFIG_EXECUTABLE ${PKG_CONFIG_EXECUTABLE} --maximum-traverse-depth=1)
+# pkg_check_modules(PC_GStreamer_NoDeps QUIET REQUIRED gstreamer-1.0 ${GStreamer_EXTRA_DEPS})
+# set(PKG_CONFIG_EXECUTABLE "${_old_pkg_config_executable}")
+
+set(GStreamer_VERSION "${PC_GStreamer_VERSION}")
+
+# Test validity of the paths
+# NOTE: only paths that must be considered are those provided by pkg-config
+# NOTE 2: also exclude sysroots
+find_path(GStreamer_INCLUDE_DIR
+    NAMES gst/gstversion.h
+    PATHS ${PC_GStreamer_INCLUDE_DIRS}
+    PATH_SUFFIXES gstreamer-1.0
+    NO_DEFAULT_PATH
+    NO_CMAKE_FIND_ROOT_PATH
+    REQUIRED
+)
+
+find_library(GStreamer_LIBRARY
+    NAMES gstreamer-1.0
+    PATHS ${PC_GStreamer_LIBRARY_DIRS}
+    NO_DEFAULT_PATH
+    NO_CMAKE_FIND_ROOT_PATH
+    REQUIRED
+)
+
+# Android: Ignore these libraries when constructing the IMPORTED_LOCATION
+set(_gst_IGNORED_SYSTEM_LIBRARIES c c++ unwind m dl atomic)
+if (ANDROID)
+    list(APPEND _gst_IGNORED_SYSTEM_LIBRARIES log GLESv2 EGL OpenSLES android)
+elseif(APPLE)
+    list(APPEND _gst_IGNORED_SYSTEM_LIBRARIES iconv resolv System)
+endif()
+
+# Normalize library flags coming from srt/haisrt
+# https://github.com/Haivision/srt/commit/b90b64d26f850fb0efcc4cdd8b31cbf74bd4db0c
+set(_gst_SRT_REGEX_PATCH "^:lib(.+)\\.(a|so|lib|dylib)$")
+
+if(PC_GStreamer_FOUND AND (NOT TARGET GStreamer::GStreamer))
+    # This is not UNKNOWN but INTERFACE, as we only intend to
+    # make a target suitable for downstream consumption.
+    # FindPkgConfig already takes care of things, however it is totally unable
+    # to discern between shared and static libraries when populating
+    # xxx_STATIC_LINK_LIBRARIES, so we need to populate them manually.
+    add_library(GStreamer::GStreamer INTERFACE IMPORTED)
+
+    if (GStreamer_USE_STATIC_LIBS)
+        _gst_filter_missing_directories(PC_GStreamer_STATIC_INCLUDE_DIRS)
+        set_target_properties(GStreamer::GStreamer PROPERTIES
+            INTERFACE_COMPILE_OPTIONS "${PC_GStreamer_STATIC_CFLAGS_OTHER}"
+        )
+        if (PC_GStreamer_STATIC_INCLUDE_DIRS)
+            set_target_properties(GStreamer::GStreamer PROPERTIES
+                INTERFACE_INCLUDE_DIRECTORIES "${PC_GStreamer_STATIC_INCLUDE_DIRS}"
+            )
+        endif()
+        _gst_apply_frameworks(PC_GStreamer_STATIC_LDFLAGS_OTHER GStreamer::GStreamer)
+    else()
+        set_target_properties(GStreamer::GStreamer PROPERTIES
+            INTERFACE_COMPILE_OPTIONS "${PC_GStreamer_CFLAGS_OTHER}"
+            INTERFACE_INCLUDE_DIRECTORIES "${PC_GStreamer_INCLUDE_DIRS}"
+            INTERFACE_LINK_OPTIONS "${PC_GStreamer_LDFLAGS_OTHER}"
+        )
+    endif()
+
+    add_library(GStreamer::deps INTERFACE IMPORTED)
+
+    if (NOT GStreamer_USE_STATIC_LIBS)
+        set_target_properties(GStreamer::deps PROPERTIES
+            INTERFACE_LINK_LIBRARIES "${PC_GStreamer_LINK_LIBRARIES}"
+        )
+        # We're done
+    else()
+        # Handle all libraries, even those specified with -l:libfoo.a (srt)
+        # Due to the unavailability of pkgconf's `--maximum-traverse-depth`
+        # on stock pkg-config, I attempt to simulate it through the shared
+        # libraries listing.
+        # If pkgconf is available, replace all PC_GStreamer_ entries with
+        # PC_GStreamer_NoDeps and uncomment the code block above.
+        foreach(LOCAL_LIB IN LISTS PC_GStreamer_LIBRARIES)
+            # list(TRANSFORM REPLACE) is of no use here
+            # https://gitlab.kitware.com/cmake/cmake/-/issues/16899
+            if (LOCAL_LIB MATCHES "${_gst_SRT_REGEX_PATCH}")
+                string(REGEX REPLACE "${_gst_SRT_REGEX_PATCH}" "\\1" LOCAL_LIB "${LOCAL_LIB}")
+            endif()
+            string(MAKE_C_IDENTIFIER "_gst_${LOCAL_LIB}" GST_LOCAL_LIB)
+            if (NOT ${GST_LOCAL_LIB})
+                _gst_find_library(${LOCAL_LIB} ${GST_LOCAL_LIB} ${PC_GStreamer_STATIC_LIBRARY_DIRS})
+            endif()
+            target_link_libraries(GStreamer::GStreamer INTERFACE
+                "${${GST_LOCAL_LIB}}"
+            )
+        endforeach()
+
+        _gst_apply_link_libraries(ON PC_GStreamer_STATIC_LIBRARIES PC_GStreamer_STATIC_LIBRARY_DIRS GStreamer::deps)
+    endif()
+
+    target_link_libraries(GStreamer::GStreamer
+        INTERFACE
+            GStreamer::deps
+    )
+endif()
+
+foreach(_gst_PLUGIN IN LISTS GSTREAMER_PLUGINS)
+    # Safety valve for the custom targets above
+    if ("${_gst_plugin}" IN_LIST _gst_CUSTOM_TARGETS)
+        continue()
+    endif()
+
+    if (TARGET GStreamer::${_gst_PLUGIN})
+        continue()
+    endif()
+
+    if (GStreamer_FIND_REQUIRED_${_gst_PLUGIN})
+        set(_gst_PLUGIN_REQUIRED REQUIRED)
+    else()
+        set(_gst_PLUGIN_REQUIRED)
+    endif()
+
+    pkg_check_modules(PC_GStreamer_${_gst_PLUGIN} "gst${_gst_PLUGIN}")
+
+    set(GStreamer_${_gst_PLUGIN}_FOUND "${PC_GStreamer_${_gst_PLUGIN}_FOUND}")
+    if (NOT GStreamer_${_gst_PLUGIN}_FOUND)
+        continue()
+    endif()
+
+    add_library(GStreamer::${_gst_PLUGIN} INTERFACE IMPORTED)
+    _gst_filter_missing_directories(PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS)
+    set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+        INTERFACE_COMPILE_OPTIONS "${PC_GStreamer_${_gst_PLUGIN}_CFLAGS_OTHER}"
+    )
+    if (PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS)
+        set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS}"
+        )
+    endif()
+    if (GStreamer_USE_STATIC_LIBS)
+        _gst_apply_frameworks(PC_GStreamer_${_gst_PLUGIN}_STATIC_LDFLAGS_OTHER GStreamer::${_gst_PLUGIN})
+    else()
+        set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+            INTERFACE_LINK_OPTIONS "${PC_GStreamer_${_gst_PLUGIN}_LDFLAGS_OTHER}"
+            INTERFACE_LINK_LIBRARIES "${PC_GStreamer_${_gst_PLUGIN}_LINK_LIBRARIES}"
+        )
+        # We're done
+        continue()
+    endif()
+
+    # Handle all libraries, even those specified with -l:libfoo.a (srt)
+    _gst_apply_link_libraries(OFF PC_GStreamer_${_gst_PLUGIN}_STATIC_LIBRARIES PC_GStreamer_${_gst_PLUGIN}_STATIC_LIBRARY_DIRS GStreamer::${_gst_PLUGIN})
+endforeach()
+
+foreach(_gst_PLUGIN IN LISTS GSTREAMER_APIS)
+    # Safety valve for the custom targets above
+    if ("${_gst_plugin}" IN_LIST _gst_CUSTOM_TARGETS)
+        continue()
+    endif()
+
+    if (TARGET GStreamer::${_gst_PLUGIN})
+        continue()
+    endif()
+
+    if (GStreamer_FIND_REQUIRED_${_gst_PLUGIN})
+        set(_gst_PLUGIN_REQUIRED REQUIRED)
+    else()
+        set(_gst_PLUGIN_REQUIRED)
+    endif()
+
+    string(REGEX REPLACE "^api_(.+)" "\\1" _gst_PLUGIN_PC "${_gst_PLUGIN}")
+    string(REPLACE "_" "-" _gst_PLUGIN_PC "${_gst_PLUGIN_PC}")
+
+    pkg_check_modules(PC_GStreamer_${_gst_PLUGIN} "gstreamer-${_gst_PLUGIN_PC}-1.0")
+
+    set(GStreamer_${_gst_PLUGIN}_FOUND "${PC_GStreamer_${_gst_PLUGIN}_FOUND}")
+    if (NOT GStreamer_${_gst_PLUGIN}_FOUND)
+        continue()
+    endif()
+
+    add_library(GStreamer::${_gst_PLUGIN} INTERFACE IMPORTED)
+    _gst_filter_missing_directories(PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS)
+    set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+        INTERFACE_COMPILE_OPTIONS "${PC_GStreamer_${_gst_PLUGIN}_CFLAGS_OTHER}"
+        INTERFACE_LINK_OPTIONS "${PC_GStreamer_${_gst_PLUGIN}_LDFLAGS_OTHER}"
+    )
+    if (PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS)
+        set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${PC_GStreamer_${_gst_PLUGIN}_INCLUDE_DIRS}"
+        )
+    endif()
+    if (GStreamer_USE_STATIC_LIBS)
+        _gst_apply_frameworks(PC_GStreamer_${_gst_PLUGIN}_STATIC_LDFLAGS_OTHER GStreamer::${_gst_PLUGIN})
+    else()
+        set_target_properties(GStreamer::${_gst_PLUGIN} PROPERTIES
+            INTERFACE_LINK_OPTIONS "${PC_GStreamer_${_gst_PLUGIN}_LDFLAGS_OTHER}"
+            INTERFACE_LINK_LIBRARIES "${PC_GStreamer_${_gst_PLUGIN}_LINK_LIBRARIES}"
+        )
+        # We're done
+        continue()
+    endif()
+
+    # Handle all libraries, even those specified with -l:libfoo.a (srt)
+    _gst_apply_link_libraries(OFF PC_GStreamer_${_gst_PLUGIN}_STATIC_LIBRARIES PC_GStreamer_${_gst_PLUGIN}_STATIC_LIBRARY_DIRS GStreamer::${_gst_PLUGIN})
+endforeach()
+
+# Perform final validation
+include(FindPackageHandleStandardArgs)
+set(_gst_handle_version_range)
+if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.19.0")
+    set(_gst_handle_version_range "HANDLE_VERSION_RANGE")
+endif()
+find_package_handle_standard_args(GStreamer
+    REQUIRED_VARS
+        GStreamer_LIBRARY
+        GStreamer_INCLUDE_DIR
+    VERSION_VAR GStreamer_VERSION
+    ${_gst_handle_version_range}
+    HANDLE_COMPONENTS
+)

subprojects/gstreamer/cmake/meson.build

@@ -0,0 +1,9 @@
+find_module = files(
+    'FindGStreamer.cmake',
+)
+
+install_data(
+    find_module,
+    install_dir: get_option('datadir') / 'cmake'
+)
+

subprojects/gstreamer/meson.build

@@ -679,6 +679,7 @@ endif
 
 
 gst_libraries = []
+subdir('cmake')
 subdir('gst')
 subdir('libs')
 subdir('plugins')