[glibmm] Add dependencies to Doxygen tag files in subprojects

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 44e1ee08158fab864f84e0a283fb829ff9a3b15f
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue May 18 09:54:28 2021 +0200

    Add dependencies to Doxygen tag files in subprojects
    
    Doxygen in a main project shall not be called before tag files have been
    created or updated in subprojects.

 docs/reference/meson.build | 13 ++++++++++++-
 meson.build                |  2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)
---
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index 296f2909..923577be 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -12,12 +12,21 @@ tag_file_modules = [
   'sigc++-3.0',
 ]
 doxygen_tagfiles = ''
+doxygen_tag_targets = []
 docinstall_flags = []
 foreach module : tag_file_modules
   depmod = dependency(module, required: false)
   if depmod.found()
     doxytagfile = depmod.get_variable(pkgconfig: 'doxytagfile', internal: 'doxytagfile', default_value: '')
     if doxytagfile != ''
+      if depmod.type_name() == 'internal'
+        # Subprojects must build their tag files before doxygen is called.
+        if module.startswith('mm-common')
+          doxygen_tag_targets += subproject('mm-common').get_variable('global_tag_file_target')
+        else
+          doxygen_tag_targets += subproject(module).get_variable('global_tag_file_target')
+        endif
+      endif
       htmlrefpub = depmod.get_variable(pkgconfig: 'htmlrefpub', internal: 'htmlrefpub', default_value: '')
       htmlrefdir = depmod.get_variable(pkgconfig: 'htmlrefdir', internal: 'htmlrefdir', default_value: '')
       if htmlrefpub == ''
@@ -51,7 +60,7 @@ doc_conf_data.set('abs_top_srcdir', project_source_root)
 doc_conf_data.set('GLIBMM_MODULE_NAME', book_name)
 doc_conf_data.set('DOXYGEN_TAGFILES', doxygen_tagfiles)
 
-configure_file(
+doxyfile = configure_file(
   input: 'Doxyfile.in',
   output: '@BASENAME@',
   configuration: doc_conf_data,
@@ -122,6 +131,8 @@ tag_file = custom_target('html_and_tag',
     src_h_files,
     built_h_files,
   ],
+  depend_files: doxyfile,
+  depends: doxygen_tag_targets,
   build_by_default: build_documentation,
   install: true,
   install_dir: install_reference_docdir,
diff --git a/meson.build b/meson.build
index 0ca01cb6..252c8170 100644
--- a/meson.build
+++ b/meson.build
@@ -309,6 +309,8 @@ if meson.is_subproject()
   }
   if build_documentation
     pkgconfig_vars += {'doxytagfile': tag_file.full_path()}
+    # May be used in a main project.
+    global_tag_file_target = tag_file
   endif
   giomm_dep = declare_dependency(
     dependencies: giomm_own_dep,