[pangomm/meson.msvc: 1/7] Meson builds: Improve GIT check on MSVC builds

[Chun-wei Fan <fanchunwei src gnome org>]

commit 0b57706b4704446ea6bcf847d8303ad3c017ab74
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Thu Sep 19 17:50:41 2019 +0800

    Meson builds: Improve GIT check on MSVC builds
    
    Check that we are not attempting to build directly from a GIT
    checkout on MSVC, as this is currently not supported as m4 is required,
    which is not well supported on a Windows cmd.exe environment.

 meson.build | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index 14f1f27..e66a115 100644
--- a/meson.build
+++ b/meson.build
@@ -36,7 +36,10 @@ pangomm_libversion = '@0@.@1@.@2@'.format(
 project_source_root = meson.current_source_dir()
 project_build_root = meson.current_build_dir()
 
+cpp_compiler = meson.get_compiler('cpp')
+is_msvc = cpp_compiler.get_id() == 'msvc'
 python3 = import('python').find_installation('python3')
+
 python_version = python3.language_version()
 python_version_req = '>= 3.5'
 if not python_version.version_compare(python_version_req)
@@ -51,10 +54,15 @@ import sys
 sys.exit(0 if os.path.isdir("@0@") else 1)
 '''.format(project_source_root / '.git')
 is_git_build = run_command(python3, '-c', cmd_py).returncode() == 0
+
 # In Unix-like system, an alternative is
 # is_git_build = run_command('test', '-d', project_source_root / '.git').returncode() == 0
 # Python code can be used in all operating sytems where Meson can run.
 
+# Unfortunately due to m4 requirements, we cannot support MSVC builds
+# directly from GIT checkouts
+assert(not is_msvc or not is_git_build, 'Direct builds from GIT is not supported for MSVC builds')
+
 # Options.
 maintainer_mode_opt = get_option('maintainer-mode')
 maintainer_mode = maintainer_mode_opt == 'true' or \
@@ -114,8 +122,6 @@ if maintainer_mode and mm_common_get.found()
     project_source_root / 'untracked' / 'docs')
 endif
 
-cpp_compiler = meson.get_compiler('cpp')
-
 # Set compiler warnings.
 warning_flags = []
 if warning_level == 'min'