[mm-common] skeletonmm/meson.build: Avoid configuration warnings

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 3379d0809c55560638ee7ed1336337d4dfc86992
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri May 13 15:36:34 2022 +0200

    skeletonmm/meson.build: Avoid configuration warnings

 skeletonmm/meson.build | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)
---
diff --git a/skeletonmm/meson.build b/skeletonmm/meson.build
index c60c9b2..d1e89d4 100644
--- a/skeletonmm/meson.build
+++ b/skeletonmm/meson.build
@@ -4,7 +4,8 @@ project('skeletonmm', 'cpp',
   version: '0.1.0',
   license: 'LGPLv2.1+',
   default_options: [
-    'cpp_std=c++17'
+    'cpp_std=c++17',
+    'warning_level=1',
   ],
   meson_version: '>= 0.56.0', # required for executable(..., win_subsystem: ...)
 )
@@ -68,10 +69,12 @@ maintainer_mode = maintainer_mode_opt == 'true' or \
 if is_dist_check
   message('Looks like a tarball is being tested. ' + \
           'Option "dist-warnings" is used instead of "warnings".')
-  warning_level = get_option('dist-warnings')
+  cpp_warnings = get_option('dist-warnings')
 else
-  warning_level = get_option('warnings')
+  cpp_warnings = get_option('warnings')
 endif
+warning_level = get_option('warning_level').to_int()
+werror = get_option('werror')
 build_deprecated_api = get_option('build-deprecated-api')
 build_documentation_opt = get_option('build-documentation')
 build_documentation = build_documentation_opt == 'true' or \
@@ -164,13 +167,24 @@ perl = find_program('perl', required: maintainer_mode or \
 cpp_compiler = meson.get_compiler('cpp')
 
 # Set compiler warnings.
+# Meson warns if any of the /W1, /W2, /W3, /W4, /Wall, -Wall, -Wextra, -Werror
+# compiler options are added with add_project_arguments().
+# Avoid such warnings, when possible.
+# See _warn_about_builtin_args() in meson/mesonbuild/interpreter/interpreter.py.
 warning_flags = []
-if warning_level == 'min'
-  warning_flags = ['-Wall']
-elif warning_level == 'max' or warning_level == 'fatal'
-  warning_flags = '-pedantic -Wall -Wextra -Wformat-security -Wsuggest-override -Wshadow 
-Wno-long-long'.split()
-  if warning_level == 'fatal'
-    warning_flags += ['-Werror']
+if cpp_warnings == 'min'
+  if warning_level == 0
+    warning_flags = ['-Wall']
+  endif
+elif cpp_warnings == 'max' or cpp_warnings == 'fatal'
+  if warning_level < 3
+    warning_flags = ['-pedantic', '-Wall', '-Wextra']
+  endif
+  warning_flags += '-Wformat-security -Wsuggest-override -Wshadow -Wno-long-long'.split()
+  if cpp_warnings == 'fatal'
+    if not werror
+      warning_flags += ['-Werror']
+    endif
     deprecations = 'G SKELETON GLIBMM SIGCXX'.split()
     foreach d : deprecations
       warning_flags += '-D@0@_DISABLE_DEPRECATED'.format(d)
@@ -243,7 +257,8 @@ summary = [
   meson.project_name() + ' ' + meson.project_version(),
   '',
   '         Maintainer mode: @0@@1@'.format(maintainer_mode_opt, real_maintainer_mode),
-  '       Compiler warnings: @0@'.format(warning_level),
+  '       Compiler warnings: @0@ (warning_level: @1@, werror: @2@)'. \
+                             format(cpp_warnings, warning_level, werror),
   '    Build deprecated API: @0@'.format(build_deprecated_api),
   'Build HTML documentation: @0@@1@'.format(build_documentation_opt, real_build_documentation),
   '  Build example programs: @0@'.format(build_examples),