Machine file pkg_config_path overrides environment

This is consistent with c_args in machine file overriding CFLAGS from
env. This also spotted an issue where in a native build this resulted
in pkg_config_path being /bar instead of /foo:
`-Dpkg_config_path=/foo -Dbuild.pkg_config_path=/bar`

Fixes: #7573

mesonbuild/coredata.py

@@ -735,7 +735,9 @@ class CoreData:
         for k, v in options.items():
             if k.startswith('build.'):
                 k = k.split('.', 1)[1]
-            res[k] = v
+                res.setdefault(k, v)
+            else:
+                res[k] = v
         return res
 
     def copy_build_options_from_regular_ones(self):

mesonbuild/environment.py

@@ -629,12 +629,12 @@ class Environment:
         self.properties = properties.default_missing()
         self.cmakevars = cmakevars.default_missing()
 
-        # Environment options override those from cross/native files
-        self.set_options_from_env()
-
         # Command line options override those from cross/native files
         self.raw_options.update(options.cmd_line_options)
 
+        # Take default value from env if not set in cross/native files or command line.
+        self.set_default_options_from_env()
+
         # Warn if the user is using two different ways of setting build-type
         # options that override each other
         if 'buildtype' in self.raw_options and \
@@ -727,7 +727,7 @@ class Environment:
                 per_machine_options[build_optname] = value
         self.raw_options = per_machine_options
 
-    def set_options_from_env(self):
+    def set_default_options_from_env(self):
         for for_machine in MachineChoice:
             p_env_pair = get_env_var_pair(for_machine, self.is_cross_build(), 'PKG_CONFIG_PATH')
             if p_env_pair is not None:
@@ -746,7 +746,7 @@ class Environment:
                 # FIXME: We should remember if we took the value from env to warn
                 # if it changes on future invocations.
                 if self.first_invocation:
-                    self.raw_options[key] = p_list
+                    self.raw_options.setdefault(key, p_list)
 
     def create_new_coredata(self, options: 'argparse.Namespace') -> None:
         # WARNING: Don't use any values from coredata in __init__. It gets

run_unittests.py

@@ -8373,7 +8373,7 @@ class NativeFileTests(BasePlatformTests):
         else:
             self.fail('Did not find werror in build options?')
 
-    def test_builtin_options_env_overrides_conf(self):
+    def test_builtin_options_conf_overrides_env(self):
         testcase = os.path.join(self.common_test_dir, '2 cpp')
         config = self.helper_create_native_file({'built-in options': {'pkg_config_path': '/foo'}})
 
@@ -8381,7 +8381,7 @@ class NativeFileTests(BasePlatformTests):
         configuration = self.introspect('--buildoptions')
         for each in configuration:
             if each['name'] == 'pkg_config_path':
-                self.assertEqual(each['value'], ['/bar'])
+                self.assertEqual(each['value'], ['/foo'])
                 break
         else:
             self.fail('Did not find pkg_config_path in build options?')
@@ -8786,10 +8786,10 @@ class CrossFileTests(BasePlatformTests):
                 break
         self.assertEqual(found, 4, 'Did not find all sections.')
 
-    def test_builtin_options_env_overrides_conf(self):
+    def test_builtin_options_conf_overrides_env(self):
         testcase = os.path.join(self.common_test_dir, '2 cpp')
-        config = self.helper_create_cross_file({'built-in options': {'pkg_config_path': '/foo'}})
-        cross = self.helper_create_cross_file({'built-in options': {'pkg_config_path': '/foo'}})
+        config = self.helper_create_cross_file({'built-in options': {'pkg_config_path': '/native'}})
+        cross = self.helper_create_cross_file({'built-in options': {'pkg_config_path': '/cross'}})
 
         self.init(testcase, extra_args=['--native-file', config, '--cross-file', cross],
                   override_envvars={'PKG_CONFIG_PATH': '/bar', 'PKG_CONFIG_PATH_FOR_BUILD': '/dir'})
@@ -8797,10 +8797,10 @@ class CrossFileTests(BasePlatformTests):
         found = 0
         for each in configuration:
             if each['name'] == 'pkg_config_path':
-                self.assertEqual(each['value'], ['/bar'])
+                self.assertEqual(each['value'], ['/cross'])
                 found += 1
             elif each['name'] == 'build.pkg_config_path':
-                self.assertEqual(each['value'], ['/dir'])
+                self.assertEqual(each['value'], ['/native'])
                 found += 1
             if found == 2:
                 break