guile: deprecate; instead use scm

Deprecate the long-deprecated guile support in the build-system too.
Needs explicit -Dguile=enabled

Makefile

@@ -1,4 +1,4 @@
-## Copyright (C) 2008-2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+## Copyright (C) 2008-2026 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
@@ -33,13 +33,13 @@ ifneq ($(V),0)
   VERBOSE=--verbose
 endif
 
-# when MU_HACKER is set, do a debug build
+# when MU_HACKER is set, do a debug build MU_HACKER is for djcb & compatible
-# MU_HACKER is for djcb & compatible developers
+# developers note that mu requires C++20, we only pass C++23 here for the better
-# note that mu uses C++17, we only pass C++23 here
+# error messages (esp. for fmt).
-# for the better error messages (esp. for fmt).
 ifneq (${MU_HACKER},)
 MESON_FLAGS:=$(MESON_FLAGS) '-Dbuildtype=debug'    \
 			    '-Dreadline=enabled'   \
+			    '-Dguile=enabled'      \
 			    '-Dcpp_std=c++23'
 endif
 

meson.build

@@ -208,13 +208,7 @@ gio_unix_dep   = dependency('gio-unix-2.0', version: '>= 2.80')
 
 # gmime
 gmime_dep       = dependency('gmime-3.0', version: '>= 3.2.13')
-
+# 3.2.13 version has  g_mime_object_write_content_to_stream
-# note: g_mime_object_write_content_to_stream is not available
-# in the gmime we still support for normal mu build.; we only need
-# for scm (see beloww)
-gmime_scm_ok = cc.has_function('g_mime_object_write_content_to_stream',
-                               prefix : '#include <gmime/gmime.h>',
-                               dependencies: gmime_dep)
 
 thread_dep     = dependency('threads')
 
@@ -278,9 +272,11 @@ endif
 #
 # guile
 
-guile_dep = dependency('guile-3.0', required: get_option('guile'))
+guile_required=get_option('guile').enabled() or get_option('scm').enabled()
-# allow for a custom guile-extension-dir
+guile_dep = dependency('guile-3.0', required: guile_required)
-if guile_dep.found()
+
+# allow for a custom guile-extension-dir (for old-style guile-support)
+if guile_dep.found() and get_option('guile').enabled()
   custom_guile_xd=get_option('guile-extension-dir')
   if custom_guile_xd == ''
     guile_extension_dir = guile_dep.get_variable(pkgconfig: 'extensiondir')
@@ -341,21 +337,27 @@ install_data('NEWS.org', 'IDEAS.org',
 subdir('lib')
 
 # this must happen _after_ subdir('lib')
-if not get_option('guile').disabled() and guile_dep.found()
+if guile_dep.found()
-  config_h_data.set('BUILD_GUILE', 1)
+
-  config_h_data.set_quoted('GUILE_BINARY',
+  # modern guile support
+  if not get_option('scm').disabled() and guile_dep.found()
+    config_h_data.set('BUILD_SCM', 1)
+    subdir('scm')
+  else
+    # dummy-dep.
+    mu_scm_dep = declare_dependency()
+  endif
+
+  # old-style guile-support (deprecated)
+  if not get_option('guile').disabled()
+    message('old-style gulie support is deprecated')
+    config_h_data.set('BUILD_GUILE', 1)
+    config_h_data.set_quoted('GUILE_BINARY',
                            guile_dep.get_variable(pkgconfig: 'guile'))
-  subdir('guile')
+    subdir('guile')
-endif
+  endif
 
-# this must happen _after_ subdir('lib')
 
-if not get_option('scm').disabled() and guile_dep.found() and gmime_scm_ok
-  config_h_data.set('BUILD_SCM', 1)
-  subdir('scm')
-else
-  # dummy-dep.
-  mu_scm_dep = declare_dependency()
 endif
 
 subdir('mu')

meson_options.txt

@@ -1,4 +1,4 @@
-## Copyright (C) 2022-2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+## Copyright (C) 2022-2026 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
@@ -54,24 +54,27 @@ option('lispdir',
 
 
 #
-# guile & scm
+# scm & guile (both use GNU Guile)
 #
-
+option('scm',
-option('guile',
        type : 'feature',
        value: 'auto',
        description: 'build the guile scripting support (requires guile-3.x)')
 
+
+# old-style guile has been deprecated for years, and is now
+# disabled by default. It will be removed in some future release.
+option('guile',
+       type : 'feature',
+       value: 'disabled',
+       deprecated: true,
+       description: 'build the guile scripting support (requires guile-3.x)')
+
 # by default, this uses guile_dep.get_variable(pkgconfig: 'extensiondir')
 option('guile-extension-dir',
        type: 'string',
        description: 'custom install path for the guile extension module')
 
-option('scm',
-       type : 'feature',
-       value: 'auto',
-       description: 'build the guile scripting support (requires guile-3.x)')
-
 #
 # misc
 #