build: use date.py instead of date

MacOS (and others) "date" command don't support all the options that GNU
date has. So don't depend on that, add a small python program for this.

.gitignore

@@ -105,7 +105,6 @@ configure.lineno
 /lib/doxyfile
 /version.texi
 /compile
-build-aux/
 /TAGS
 parse
 

build-aux/date.py

@@ -0,0 +1,9 @@
+#!/bin/env python
+#The MacOS 'date' is not quite up to GNU standards
+import sys
+from datetime import datetime
+date=datetime.strptime(sys.argv[1],'%Y-%m-%d')
+print(date.strftime(sys.argv[2]))
+#
+#  ./date.py 2023-10-14 "The year-month is %y %m"
+#

meson.build

@@ -99,21 +99,22 @@ endforeach
 cxx.check_header('charconv', required:true)
 
 
+build_aux = join_paths(meson.current_source_dir(), 'build-aux')
 ################################################################################
 # derived date values (based on 'mu-date'); used in docs
-date=find_program('date', required:true)
+# we can't use the 'date' because MacOS 'date' is incompatible with GNU's.
+pdate=join_paths(build_aux, 'date.py')
 env = environment()
 env.set('LANG', 'C')
-mu_day_month_year = run_command(date, '-u', '+%d %B %Y', '--date', mu_date,
+mu_day_month_year = run_command(pdate, mu_date, '%d %B %Y',
                                 check:true, capture:true,
                                 env: env).stdout().strip()
-mu_month_year = run_command(date, '-u', '+%B %Y', '--date', mu_date,
+mu_month_year = run_command(pdate, mu_date, '%B %Y',
                             check:true, capture:true,
                             env: env).stdout().strip()
-mu_year = run_command(date, '-u', '+%Y', '--date', mu_date,
+mu_year = run_command(pdate, mu_date, '%Y',
                       check:true, capture:true, env: env).stdout().strip()
 
-
 ################################################################################
 # config.h setup
 #
@@ -239,8 +240,7 @@ else
   if not install_info.found()
     message('install-info not found')
   else
-    install_info_script=join_paths(meson.current_source_dir(), 'build-aux',
-                                   'meson-install-info.sh')
+    install_info_script=join_paths(build_aux, 'meson-install-info.sh')
   endif
 endif
 
@@ -267,7 +267,7 @@ version_texi_data.set('UPDATED', mu_day_month_year)
 version_texi_data.set('UPDATEDMONTH', mu_month_year)
 version_texi_data.set('UPDATEDYEAR', mu_year)
 
-configure_file(input: join_paths('build-aux', 'version.texi.in'),
+configure_file(input: join_paths(build_aux, 'version.texi.in'),
                output: 'version.texi',
                configuration: version_texi_data)