[gtkmm] meson.build: Don't use deprecated execute(..., gui_app: ...)

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 1ff8f899aa652fc167954311c5d910432f773d98
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri Feb 18 12:19:16 2022 +0100

    meson.build: Don't use deprecated execute(..., gui_app: ...)
    
    Don't use deprecated python3.path() and execute(..., gui_app: ...).
    Let import('python').find_installation() always find the python
    installation used to run Meson.
    Fixes #111

 demos/gtk-demo/meson.build | 2 +-
 docs/reference/meson.build | 4 ++--
 gdk/gdkmm/meson.build      | 4 ++--
 gtk/gtkmm/meson.build      | 4 ++--
 meson.build                | 9 ++++-----
 tests/meson.build          | 2 +-
 6 files changed, 12 insertions(+), 13 deletions(-)
---
diff --git a/demos/gtk-demo/meson.build b/demos/gtk-demo/meson.build
index 9211c9c2..a4428b96 100644
--- a/demos/gtk-demo/meson.build
+++ b/demos/gtk-demo/meson.build
@@ -48,7 +48,7 @@ if epoxy_dep.found()
     gtkmm_demo_cc_files, demo_resources,
     dependencies: [gtkmm_own_dep, epoxy_dep],
     implicit_include_directories: false,
-    gui_app: true,
+    win_subsystem: 'windows',
     build_by_default: build_demos,
     link_args: gui_app_ldflags,
     install: false,
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index 32bb9f8b..617d367a 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -154,7 +154,7 @@ devhelp_file = custom_target('devhelp',
 
 # Install Devhelp file and html files.
 meson.add_install_script(
-  python3.path(), doc_reference_py, 'install_doc',
+  python3, doc_reference_py, 'install_doc',
   doctool_dir,
   devhelp_file.full_path(),
   install_devhelpdir,
@@ -177,7 +177,7 @@ install_data(image_files, install_dir: install_image_docdir)
 if can_add_dist_script
   # Distribute built files and files copied by mm-common-get.
   meson.add_dist_script(
-    python3.path(), doc_reference_py, 'dist_doc',
+    python3, doc_reference_py, 'dist_doc',
     doctool_dir,
     doctool_dist_dir,
     meson.current_build_dir(),
diff --git a/gdk/gdkmm/meson.build b/gdk/gdkmm/meson.build
index 0b5e20e8..de322c44 100644
--- a/gdk/gdkmm/meson.build
+++ b/gdk/gdkmm/meson.build
@@ -256,7 +256,7 @@ gdkmm_library = static_library('gdkmm',
 
 # Install built .h and _p.h files.
 meson.add_install_script(
-  python3.path(), generate_binding_py, 'install_built_h_files',
+  python3, generate_binding_py, 'install_built_h_files',
   built_h_cc_dir,
   install_includedir / gtkmm_pcname / 'gdkmm', # subdir below {prefix}
   gdkmm_used_hg_ccg_basenames
@@ -265,7 +265,7 @@ meson.add_install_script(
 if can_add_dist_script
   # Distribute built files.
   meson.add_dist_script(
-    python3.path(), generate_binding_py, 'dist_built_files',
+    python3, generate_binding_py, 'dist_built_files',
     built_h_cc_dir,
     untracked_gdkmm,
     gdkmm_hg_ccg_basenames,
diff --git a/gtk/gtkmm/meson.build b/gtk/gtkmm/meson.build
index af74a196..a04013ab 100644
--- a/gtk/gtkmm/meson.build
+++ b/gtk/gtkmm/meson.build
@@ -507,7 +507,7 @@ gtkmm_library = library(gtkmm_libname, extra_gtkmm_objects,
 
 # Install built .h and _p.h files.
 meson.add_install_script(
-  python3.path(), generate_binding_py, 'install_built_h_files',
+  python3, generate_binding_py, 'install_built_h_files',
   built_h_cc_dir,
   install_includedir / gtkmm_pcname / 'gtkmm', # subdir below {prefix}
   gtkmm_used_hg_ccg_basenames
@@ -516,7 +516,7 @@ meson.add_install_script(
 if can_add_dist_script
   # Distribute built files.
   meson.add_dist_script(
-    python3.path(), generate_binding_py, 'dist_built_files',
+    python3, generate_binding_py, 'dist_built_files',
     built_h_cc_dir,
     untracked_gtkmm,
     gtkmm_hg_ccg_basenames,
diff --git a/meson.build b/meson.build
index 71e7b23c..722f5a36 100644
--- a/meson.build
+++ b/meson.build
@@ -7,8 +7,7 @@ project('gtkmm', 'c', 'cpp',
   default_options: [
     'cpp_std=c++17'
   ],
-  meson_version: '>= 0.54.0', # required for meson.override_dependency()
-                              # and dep.get_variable(internal:)
+  meson_version: '>= 0.56.0', # required for executable(win_subsystem:)
 )
 
 gtkmm_api_version = '4.0'
@@ -46,7 +45,7 @@ project_build_root = meson.current_build_dir()
 cpp_compiler = meson.get_compiler('cpp')
 is_msvc = cpp_compiler.get_id() == 'msvc'
 is_host_windows = host_machine.system() == 'windows'
-python3 = import('python').find_installation('python3')
+python3 = import('python').find_installation()
 
 python_version = python3.language_version()
 python_version_req = '>= 3.5'
@@ -289,7 +288,7 @@ subdir('docs/reference')
 if can_add_dist_script
   # Add a ChangeLog file to the distribution directory.
   meson.add_dist_script(
-    python3.path(), dist_changelog_py,
+    python3, dist_changelog_py,
     project_source_root,
   )
 
@@ -304,7 +303,7 @@ if can_add_dist_script
   # Add build scripts to the distribution directory, and delete .gitignore
   # files and an empty $MESON_PROJECT_DIST_ROOT/build/ directory.
   meson.add_dist_script(
-    python3.path(), dist_build_scripts_py,
+    python3, dist_build_scripts_py,
     project_source_root,
     'untracked' / 'build_scripts',
     dont_distribute,
diff --git a/tests/meson.build b/tests/meson.build
index d512c7d8..ecb32c2d 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -36,7 +36,7 @@ foreach ex : test_programs
   exe_file = executable(ex_name, ex_sources,
     dependencies: gtkmm_own_dep,
     implicit_include_directories: false,
-    gui_app: ex[3],
+    win_subsystem: ex[3] ? 'windows' : 'console',
     build_by_default: build_tests,
     link_args: ex[3] ? gui_app_ldflags : [],
     install: false,