scm: new guile/scheme bindings

This implements the new scm/guile bindings for mu, to replace the deprecated
guile/ (at some point in the future).

For now, we allow for creating a guile shell with mu support.

scm/meson.build

@@ -0,0 +1,58 @@
+## Copyright (C) 2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software Foundation,
+## Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+mu_scm_dir=join_paths(datadir, 'mu', 'scm')
+mu_scm_dir_arg='-DMU_SCM_DIR="' + mu_scm_dir + '"'
+
+lib_mu_scm=static_library(
+  'mu-scm',
+  [
+    'mu-scm.cc',
+    'mu-scm-contact.cc',
+    'mu-scm-store.cc'
+  ],
+  dependencies: [
+    guile_dep,
+    config_h_dep,
+    lib_mu_dep,
+    lib_mu_utils_dep,
+    lib_mu_message_dep],
+  install: false,
+  cpp_args: [mu_scm_dir_arg])
+
+install_data(['mu-scm.scm', 'mu-scm-shell.scm'], install_dir : mu_scm_dir)
+
+# note: top-level meson.build defines a dummy replacement for this.
+mu_scm_dep = declare_dependency(
+  link_with: lib_mu_scm,
+  dependencies: [guile_dep, lib_mu_dep, config_h_dep, thread_dep ],
+  include_directories:
+    include_directories(['.', '..']))
+
+if makeinfo.found()
+  custom_target('mu_scm_info',
+                input: 'mu-scm.texi',
+                output: 'mu-scm.info',
+                install: true,
+                install_dir: infodir,
+                command: [makeinfo,
+                          '-o', join_paths(meson.current_build_dir(), 'mu-scm.info'),
+                          join_paths(meson.current_source_dir(), 'mu-scm.texi'),
+                          '-I', join_paths(meson.current_build_dir(), '..')])
+  if install_info.found()
+    infodir = join_paths(get_option('prefix') / get_option('infodir'))
+    meson.add_install_script(install_info_script, infodir, 'mu-scm.info')
+  endif
+endif