Get 'pure_c' from environment variable CONAN_PURE_C (#587)

Co-authored-by: Dmitriy Vetutnev <d.vetutnev@gmail.com>

README.md

@@ -1364,6 +1364,7 @@ Check [Conan Build policies](https://docs.conan.io/en/latest/mastering/policies.
 - **CONAN_FORCE_SELINUX**: Force docker to relabel file objects on the shared volumes
 - **CONAN_SKIP_RECIPE_EXPORT**: If defined, the package recipe will only be exported on the first build.
 - **CPT_UPDATE_DEPENDENCIES**: Update all dependencies before building e.g conan create -u
+- **CONAN_PURE_C**: Set `pure_c` by environment variable, default `True`
 
 
 # Full example

cpt/packager.py

@@ -449,7 +449,7 @@ def named_builds(self, confs):
     def login(self, remote_name):
         self.auth_manager.login(remote_name)
 
-    def add_common_builds(self, shared_option_name=None, pure_c=True,
+    def add_common_builds(self, shared_option_name=None, pure_c=None,
                           dll_with_static_runtime=False, reference=None, header_only=True,
                           build_all_options_values=None):
         if reference:
@@ -468,6 +468,9 @@ def add_common_builds(self, shared_option_name=None, pure_c=True,
             env_shared_option_name = os.getenv("CONAN_SHARED_OPTION_NAME", None)
             shared_option_name = env_shared_option_name if str(env_shared_option_name).lower() != "false" else False
 
+        if pure_c is None:
+            pure_c = get_custom_bool_from_env("CONAN_PURE_C", True)
+
         build_all_options_values = build_all_options_values or split_colon_env("CONAN_BUILD_ALL_OPTIONS_VALUES") or []
         if not isinstance(build_all_options_values, list):
             raise Exception("'build_all_options_values' must be a list. e.g. ['foo:opt', 'foo:bar']")

cpt/test/unit/packager_test.py

@@ -1141,6 +1141,52 @@ def test_lockfile(self):
             builder.run()
             self.assertEquals("couse.lock", self.conan_api.calls[-1].kwargs["lockfile"])
 
+    def test_pure_c_env_var(self):
+
+        builder = ConanMultiPackager(gcc_versions=["8"], archs=["x86_64"], build_types=["Release"],
+                                     username="Pepe", channel="testing",
+                                     reference="Hello/0.1",
+                                     platform_info=platform_mock_for("Linux"),
+                                     ci_manager=self.ci_manager)
+        builder.add_common_builds()
+        expected = [({'arch': 'x86_64', 'build_type': 'Release',
+                      'compiler': 'gcc',
+                      'compiler.version': '8'},
+                     {},
+                     {},
+                     {})]
+        self.assertEquals([tuple(a) for a in builder.builds], expected)
+
+        builder.builds = []
+        with tools.environment_append({"CONAN_PURE_C": "True"}):
+            builder.add_common_builds()
+        expected = [({'arch': 'x86_64', 'build_type': 'Release',
+                      'compiler': 'gcc',
+                      'compiler.version': '8'},
+                     {},
+                     {},
+                     {})]
+        self.assertEquals([tuple(a) for a in builder.builds], expected)
+
+        builder.builds = []
+        with tools.environment_append({"CONAN_PURE_C": "False"}):
+            builder.add_common_builds()
+        expected = [({'arch': 'x86_64', 'build_type': 'Release',
+                      'compiler': 'gcc',
+                      'compiler.version': '8',
+                      'compiler.libcxx': "libstdc++"},
+                     {},
+                     {},
+                     {}),
+                    ({'arch': 'x86_64', 'build_type': 'Release',
+                      'compiler': 'gcc',
+                      'compiler.version': '8',
+                      'compiler.libcxx': "libstdc++11"},
+                     {},
+                     {},
+                     {})]
+        self.assertEquals([tuple(a) for a in builder.builds], expected)
+
     def test_docker_cwd(self):
         cwd = os.path.join(os.getcwd(), 'subdir')
         self.packager = ConanMultiPackager(username="lasote",