skip missing interpreters config value can be overriden via cli flag

5 files changed, 69 insertions, 26 deletions

diff --git a/changelog/903.feature.rst b/changelog/903.feature.rst
new file mode 100644
index 00000000..bb700ffb
--- /dev/null
+++ b/changelog/903.feature.rst
@@ -0,0 +1 @@
+skip missing interpreters value from the config file can now be overridden via the ``--skip-missing-interpreters`` cli flag - by :user:`gaborbernat`
diff --git a/doc/config.rst b/doc/config.rst
index e56fe8de..cb47a68f 100644
--- a/doc/config.rst
+++ b/doc/config.rst
@@ -54,18 +54,18 @@ and will first lookup global tox settings in this section:
     commands = ...  # override [tox] settings for the jenkins context
     # note: for jenkins distshare defaults to ``{toxworkdir}/distshare`` (DEPRECATED)
 
-.. confval:: skip_missing_interpreters=BOOL
+.. confval:: skip_missing_interpreters=config|true|false
 
     .. versionadded:: 1.7.2
 
-    Setting this to ``True`` is equivalent of passing the
-    ``--skip-missing-interpreters`` command line option, and will force ``tox`` to
-    return success even if some of the specified environments were missing. This is
-    useful for some CI systems or running on a developer box, where you might only
-    have a subset of all your supported interpreters installed but don't want to
-    mark the build as failed because of it. As expected, the command line switch
-    always overrides this setting if passed on the invokation.
-    **Default:** ``False``
+    When skip missing interpreters is ``true`` will force ``tox`` to return success even
+    if some of the specified environments were missing. This is useful for some CI
+    systems or running on a developer box, where you might only have a subset of
+    all your supported interpreters installed but don't want to mark the build as
+    failed because of it. As expected, the command line switch always overrides
+    this setting if passed on the invocation. Setting it to ``config``
+    means that the value is read from the config file (default is ``false``).
+    **Default:** ``config``
 
 .. confval:: envlist=CSV
 
diff --git a/src/tox/config.py b/src/tox/config.py
index a7e62d52..12ac98c5 100755
--- a/src/tox/config.py
+++ b/src/tox/config.py
@@ -493,11 +493,8 @@ def tox_addoption(parser):
     parser.add_argument(
         "--alwayscopy", action="store_true", help="override alwayscopy setting to True in all envs"
     )
-    parser.add_argument(
-        "--skip-missing-interpreters",
-        action="store_true",
-        help="don't fail tests for missing interpreters",
-    )
+
+    cli_skip_missing_interpreter(parser)
     parser.add_argument(
         "--workdir",
         action="store",
@@ -780,6 +777,24 @@ def tox_addoption(parser):
     )
 
 
+def cli_skip_missing_interpreter(parser):
+    class SkipMissingInterpreterAction(argparse.Action):
+        def __call__(self, parser, namespace, values, option_string=None):
+            value = "true" if values is None else values
+            if value not in ("config", "true", "false"):
+                raise argparse.ArgumentTypeError("value must be config, true or false")
+            setattr(namespace, self.dest, value)
+
+    parser.add_argument(
+        "--skip-missing-interpreters",
+        default="config",
+        metavar="val",
+        nargs="?",
+        action=SkipMissingInterpreterAction,
+        help="don't fail tests for missing interpreters: {config,true,false} choice",
+    )
+
+
 class Config(object):
     """Global Tox config object."""
 
@@ -947,10 +962,9 @@ class ParseIni(object):
         else:
             config.toxworkdir = config.toxinidir.join(config.option.workdir, abs=True)
 
-        if not config.option.skip_missing_interpreters:
-            config.option.skip_missing_interpreters = reader.getbool(
-                "skip_missing_interpreters", False
-            )
+        if config.option.skip_missing_interpreters == "config":
+            val = reader.getbool("skip_missing_interpreters", False)
+            config.option.skip_missing_interpreters = "true" if val else "false"
 
         config.ignore_basepython_conflict = reader.getbool("ignore_basepython_conflict", False)
 
diff --git a/src/tox/session.py b/src/tox/session.py
index 97e5da19..07e99708 100644
--- a/src/tox/session.py
+++ b/src/tox/session.py
@@ -470,7 +470,7 @@ class Session:
                 )
             except tox.exception.InterpreterNotFound as e:
                 status = e
-                if self.config.option.skip_missing_interpreters:
+                if self.config.option.skip_missing_interpreters == "true":
                     default_ret_code = 0
             if status:
                 str_status = str(status)
@@ -573,7 +573,7 @@ class Session:
             status = venv.status
             if isinstance(status, tox.exception.InterpreterNotFound):
                 msg = " {}: {}".format(venv.envconfig.envname, str(status))
-                if self.config.option.skip_missing_interpreters:
+                if self.config.option.skip_missing_interpreters == "true":
                     self.report.skip(msg)
                 else:
                     retcode = 1
diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
index 8b5d2285..3b53bad2 100644
--- a/tests/unit/test_config.py
+++ b/tests/unit/test_config.py
@@ -1902,20 +1902,48 @@ class TestGlobalOptions:
             newconfig([], inisource)
 
     def test_skip_missing_interpreters_true(self, newconfig):
-        inisource = """
+        ini_source = """
             [tox]
             skip_missing_interpreters = True
         """
-        config = newconfig([], inisource)
-        assert config.option.skip_missing_interpreters
+        config = newconfig([], ini_source)
+        assert config.option.skip_missing_interpreters == "true"
 
     def test_skip_missing_interpreters_false(self, newconfig):
-        inisource = """
+        ini_source = """
             [tox]
             skip_missing_interpreters = False
         """
-        config = newconfig([], inisource)
-        assert not config.option.skip_missing_interpreters
+        config = newconfig([], ini_source)
+        assert config.option.skip_missing_interpreters == "false"
+
+    def test_skip_missing_interpreters_cli_no_arg(self, newconfig):
+        ini_source = """
+            [tox]
+            skip_missing_interpreters = False
+        """
+        config = newconfig(["--skip-missing-interpreters"], ini_source)
+        assert config.option.skip_missing_interpreters == "true"
+
+    def test_skip_missing_interpreters_cli_not_specified(self, newconfig):
+        config = newconfig([], "")
+        assert config.option.skip_missing_interpreters == "false"
+
+    def test_skip_missing_interpreters_cli_overrides_true(self, newconfig):
+        ini_source = """
+                    [tox]
+                    skip_missing_interpreters = False
+                """
+        config = newconfig(["--skip-missing-interpreters", "true"], ini_source)
+        assert config.option.skip_missing_interpreters == "true"
+
+    def test_skip_missing_interpreters_cli_overrides_false(self, newconfig):
+        ini_source = """
+                    [tox]
+                    skip_missing_interpreters = True
+                """
+        config = newconfig(["--skip-missing-interpreters", "false"], ini_source)
+        assert config.option.skip_missing_interpreters == "false"
 
     def test_defaultenv_commandline(self, newconfig):
         config = newconfig(["-epy27"], "")