libcamera/base: Validate internal headers as private

Headers which must not be exposed as part of the public libcamera API
should include base/private.h.

Any interface which includes the private.h header will only be able to
build if the libcamera_private dependency is used (or the
libcamera_base_private dependency directly).

Build targets which are intended to use the private API's will use the
libcamera_private to handle the automatic definition of the inclusion
guard.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/base/meson.build

@@ -21,10 +21,15 @@ libcamera_base_deps = [
     dependency('threads'),
 ]
 
+# Internal components must use the libcamera_base_private dependency to enable
+# the use of headers which must not be exposed to the libcamera public api.
+libcamera_base_args = [ '-DLIBCAMERA_BASE_PRIVATE' ]
+
 libcamera_base_lib = shared_library('libcamera-base',
                                     [libcamera_base_sources, libcamera_base_headers],
                                     name_prefix : '',
                                     install : true,
+                                    cpp_args : libcamera_base_args,
                                     include_directories : libcamera_includes,
                                     dependencies : libcamera_base_deps)
 
@@ -39,3 +44,6 @@ pkg_mod.generate(libcamera_base_lib,
                  version : '1.0',
                  description : 'Camera support base utility library',
                  subdirs : 'libcamera')
+
+libcamera_base_private = declare_dependency(dependencies : libcamera_base,
+                                            compile_args : libcamera_base_args)

src/libcamera/meson.build

@@ -112,6 +112,7 @@ endif
 libcamera_deps = [
     libatomic,
     libcamera_base,
+    libcamera_base_private,
     libdl,
     libgnutls,
     liblttng,
@@ -143,9 +144,15 @@ libcamera_dep = declare_dependency(sources : [
                                        libcamera_generated_ipa_headers,
                                    ],
                                    include_directories : libcamera_includes,
-                                   dependencies: libcamera_base,
+                                   dependencies : libcamera_base,
                                    link_with : libcamera)
 
+# Internal dependency for components and plugins which can use private APIs
+libcamera_private = declare_dependency(dependencies : [
+                                           libcamera_dep,
+                                           libcamera_base_private,
+                                       ])
+
 pkg_mod = import('pkgconfig')
 pkg_mod.generate(libcamera,
                  libraries : libcamera_base_lib,

src/libcamera/proxy/worker/meson.build

@@ -21,7 +21,7 @@ foreach mojom : ipa_mojoms
                        [worker, libcamera_generated_ipa_headers],
                        install : true,
                        install_dir : proxy_install_dir,
-                       dependencies : libcamera_dep)
+                       dependencies : libcamera_private)
 endforeach
 
 config_h.set('IPA_PROXY_DIR',