Generate a CMake file that locates the debian13 dependencies

Install ${PREFIX}/share/source-stack/source-stack.cmake as the last step. It
mirrors the image's ENV block (prefix, pkg-config and library paths) for
CMake and can restrict lookups to the prefix with GW_SOURCE_STACK_ONLY.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

debian13/source-stack.cmake.in

@@ -0,0 +1,52 @@
+# Generated into the image at ${PREFIX}/share/source-stack/source-stack.cmake.
+#
+# Points CMake at the dependencies installed by this image. It mirrors the
+# Dockerfile's ENV block (PATH, PKG_CONFIG_PATH, CMAKE_PREFIX_PATH,
+# C_INCLUDE_PATH/CPLUS_INCLUDE_PATH, LIBRARY_PATH) for CMake's own lookups.
+# The prefix is derived from this file's location, so it also works when the
+# prefix is moved. Include it after project(), before the first find_package().
+#
+#   GW_SOURCE_STACK_ONLY  resolve libraries and packages only below the prefix
+
+option(GW_SOURCE_STACK_ONLY
+    "Resolve libraries and packages only below the source-stack prefix" OFF)
+
+get_filename_component(_ss_p "${CMAKE_CURRENT_LIST_DIR}/../.." ABSOLUTE)
+set(_ss_multiarch "@MULTIARCH@")
+
+list(PREPEND CMAKE_PREFIX_PATH "${_ss_p}")
+list(PREPEND CMAKE_PROGRAM_PATH "${_ss_p}/bin")
+list(PREPEND CMAKE_INCLUDE_PATH "${_ss_p}/include")
+list(PREPEND CMAKE_LIBRARY_PATH "${_ss_p}/lib/${_ss_multiarch}" "${_ss_p}/lib")
+
+# pkg_check_modules() reads PKG_CONFIG_PATH at call time.
+set(_ss_pc "${_ss_p}/lib/${_ss_multiarch}/pkgconfig:${_ss_p}/lib/pkgconfig:${_ss_p}/share/pkgconfig")
+if(GW_SOURCE_STACK_ONLY)
+    # PKG_CONFIG_LIBDIR replaces the default search path, so system .pc files are ignored.
+    set(ENV{PKG_CONFIG_LIBDIR} "${_ss_pc}")
+    set(ENV{PKG_CONFIG_PATH} "")
+    # Build tools come from the system; look them up before system paths are switched off.
+    find_program(PKG_CONFIG_EXECUTABLE NAMES pkg-config pkgconf)
+    set(CMAKE_FIND_USE_CMAKE_SYSTEM_PATH OFF)
+    set(CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH OFF)
+    set(CMAKE_FIND_ROOT_PATH "${_ss_p}")
+    set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+    set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+    set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+else()
+    if(NOT "$ENV{PKG_CONFIG_PATH}" STREQUAL "")
+        set(ENV{PKG_CONFIG_PATH} "${_ss_pc}:$ENV{PKG_CONFIG_PATH}")
+    else()
+        set(ENV{PKG_CONFIG_PATH} "${_ss_pc}")
+    endif()
+endif()
+
+# protoc installed next to the libraries, unless the caller chose one.
+if(NOT Protobuf_PROTOC_EXECUTABLE AND EXISTS "${_ss_p}/bin/protoc")
+    set(Protobuf_PROTOC_EXECUTABLE "${_ss_p}/bin/protoc" CACHE FILEPATH "protoc")
+endif()
+
+message(STATUS "source-stack: ${_ss_p} (${_ss_multiarch})")
+unset(_ss_p)
+unset(_ss_multiarch)
+unset(_ss_pc)