modules/rust: inject a C/C++ standard for bindgen

Especially for C++ this is very important.

docs/markdown/snippets/rust-bindgen-std.md

@@ -0,0 +1,3 @@
+## Bindgen now uses the same C/C++ as the project as a whole
+
+Which is very important for C++ bindings.

mesonbuild/modules/rust.py

@@ -268,6 +268,23 @@ def bindgen(self, state: ModuleState, args: T.List, kwargs: FuncBindgen) -> Modu
         if language == 'cpp':
             clang_args.extend(['-x', 'c++'])
 
+        # Add the C++ standard to the clang arguments. Attempt to translate VS
+        # extension versions into the nearest standard version
+        std = state.get_option('std', lang=language)
+        assert isinstance(std, str), 'for mypy'
+        if std.startswith('vc++'):
+            if std.endswith('latest'):
+                mlog.warning('Attempting to translate vc++latest into a clang compatible version.',
+                             'Currently this is hardcoded for c++20', once=True, fatal=False)
+                std = 'c++20'
+            else:
+                mlog.debug('The current C++ standard is a Visual Studio extension version.',
+                           'bindgen will use a the nearest C++ standard instead')
+                std = std[1:]
+
+        if std != 'none':
+            clang_args.append(f'-std={std}')
+
         cmd = self._bindgen_bin.get_command() + \
             [
                 '@INPUT@', '--output',

test cases/rust/12 bindgen/meson.build

@@ -1,7 +1,11 @@
 # SPDX-license-identifer: Apache-2.0
-# Copyright © 2021-2022 Intel Corporation
+# Copyright © 2021-2024 Intel Corporation
 
-project('rustmod bindgen', ['c', 'cpp', 'rust'], meson_version : '>= 0.63')
+project(
+  'rustmod bindgen',
+  ['c', 'cpp', 'rust'],
+  meson_version : '>= 0.63',
+  default_options : ['cpp_std=c++17'])
 
 prog_bindgen = find_program('bindgen', required : false)
 if not prog_bindgen.found()

test cases/rust/12 bindgen/test.json

@@ -4,7 +4,7 @@
   },
   "stdout": [
     {
-      "line": "test cases/rust/12 bindgen/meson.build:38: WARNING: Project targets '>= 0.63' but uses feature introduced in '1.0.0': \"rust.bindgen\" keyword argument \"include_directories\" of type array[str]."
+      "line": "test cases/rust/12 bindgen/meson.build:42: WARNING: Project targets '>= 0.63' but uses feature introduced in '1.0.0': \"rust.bindgen\" keyword argument \"include_directories\" of type array[str]."
     }
   ]
 }