- Feature: add backend support to MesonToolchain

conan/tools/meson/toolchain.py

@@ -41,6 +41,7 @@ class MesonToolchain(object):
     {% if b_ndebug %}b_ndebug = {{b_ndebug}}{% endif %}
     {% if b_staticpic %}b_staticpic = {{b_staticpic}}{% endif %}
     {% if cpp_std %}cpp_std = {{cpp_std}}{% endif %}
+    {% if backend %}backend = {{backend}}{% endif %}
     c_args = {{c_args}} + preprocessor_definitions
     c_link_args = {{c_link_args}}
     cpp_args = {{cpp_args}} + preprocessor_definitions
@@ -66,8 +67,9 @@ class MesonToolchain(object):
     endian = {{endian}}
     """)
 
-    def __init__(self, conanfile):
+    def __init__(self, conanfile, backend=None):
         self._conanfile = conanfile
+        self._backend = self._get_backend(backend)
         self._build_type = self._conanfile.settings.get_safe("build_type")
         self._base_compiler = self._conanfile.settings.get_safe("compiler.base") or \
                               self._conanfile.settings.get_safe("compiler")
@@ -99,6 +101,7 @@ def from_build_env(name):
         self.buildtype = self._to_meson_build_type(self._build_type) if self._build_type else None
         self.default_library = self._to_meson_shared(self._shared) \
             if self._shared is not None else None
+        self.backend = self._to_meson_value(self._backend)
 
         # https://mesonbuild.com/Builtin-options.html#base-options
         self.b_vscrt = self._to_meson_vscrt(self._vscrt)
@@ -117,6 +120,19 @@ def from_build_env(name):
 
         check_using_build_profile(self._conanfile)
 
+    def _get_backend(self, recipe_backend):
+        # Returns the name of the backend used by Meson
+        conanfile = self._conanfile
+        # Downstream consumer always higher priority
+        backend_conf = conanfile.conf["tools.meson.mesontoolchain:backend"]
+        if backend_conf:
+            return backend_conf
+        # second priority: the recipe one:
+        if recipe_backend:
+            return recipe_backend
+        # if not defined, deduce automatically the default one (ninja)
+        return 'ninja'
+
     @staticmethod
     def _to_meson_value(value):
         # https://mesonbuild.com/Machine-files.html#data-types
@@ -211,6 +227,7 @@ def _context(self):
             # https://mesonbuild.com/Builtin-options.html#core-options
             "buildtype": self.buildtype,
             "default_library": self.default_library,
+            "backend": self.backend,
             # https://mesonbuild.com/Builtin-options.html#base-options
             "b_vscrt": self.b_vscrt,
             "b_staticpic": self.b_staticpic,

conans/test/integration/toolchains/meson/test_backend.py

@@ -0,0 +1,57 @@
+import os
+import platform
+import sys
+import textwrap
+
+import pytest
+
+from conans.test.assets.sources import gen_function_cpp
+from conans.test.utils.tools import TestClient
+
+
+@pytest.mark.tool_meson
+@pytest.mark.skipif(sys.version_info.major == 2, reason="Meson not supported in Py2")
+@pytest.mark.skipif(platform.system() != "Windows", reason="requires Windows")
+def test_cross_x86():
+    conanfile_py = textwrap.dedent("""
+        from conans import ConanFile, tools
+        from conan.tools.meson import Meson, MesonToolchain
+
+
+        class App(ConanFile):
+            settings = "os", "arch", "compiler", "build_type"
+            options = {"shared": [True, False], "fPIC": [True, False]}
+            default_options = {"shared": False, "fPIC": True}
+
+            def config_options(self):
+                if self.settings.os == "Windows":
+                    del self.options.fPIC
+
+            def generate(self):
+                tc = MesonToolchain(self, backend='vs')
+                tc.generate()
+
+            def build(self):
+                meson = Meson(self)
+                meson.configure()
+                meson.build()
+        """)
+    meson_build = textwrap.dedent("""
+        project('tutorial', 'cpp')
+        executable('demo', 'main.cpp')
+        """)
+    main_cpp = gen_function_cpp(name="main")
+    client = TestClient()
+    client.save({"conanfile.py": conanfile_py,
+                 "meson.build": meson_build,
+                 "main.cpp": main_cpp})
+    client.run("install .")
+    content = client.load("conan_meson_native.ini")
+    assert "backend = 'vs'" in content
+    client.run("build .")
+    assert "Auto detected Visual Studio backend" in client.out
+    client.run_command(os.path.join("build", "demo"))
+
+    assert "main _M_X64 defined" in client.out
+    assert "main _MSC_VER19" in client.out
+    assert "main _MSVC_LANG2014" in client.out