expand section names (tox-dev#1545)

* expand section names

* fix linting

* Added changelog

* trim whitespaces around factor names

* added docs

docs/changelog/1545.feature.rst

@@ -0,0 +1 @@
+Allow generative section name expansion. - by :user:`bruchar1`

docs/config.rst

@@ -830,6 +830,27 @@ are stripped, so the following line defines the same environment names::
         flake
 
 
+.. _generative-sections:
+
+Generative section names
+++++++++++++++++++++++++
+
+.. versionadded:: 3.15
+
+Using similar syntax, it is possible to generate sections::
+
+    [testenv:py{27,36}-flake]
+
+This is equivalent to defining distinct sections::
+
+    $ tox -a
+    py27-flake
+    py36-flake
+
+It is useful when you need an environment different from the default one,
+but still want to take advantage of factor-conditional settings.
+
+
 .. _factors:
 
 Factors and factor-conditional settings

docs/example/basic.rst

@@ -372,6 +372,29 @@ use :ref:`generative-envlist` and :ref:`conditional settings <factors>` to expre
         # mocking sqlite on 2.7 and 3.6 if factor "sqlite" is present
         py{27,36}-sqlite: mock
 
+
+Using generative section names
+------------------------------
+
+Suppose you have some binary packages, and need to run tests both in 32 and 64 bits.
+You also want an environment to create your virtual env for the developers.
+
+.. code-block:: ini
+
+    [testenv]
+    basepython =
+        py38-x86: python3.8-32
+        py38-x64: python3.8-64
+    commands = pytest
+
+    [testenv:py38-{x86,x64}-venv]
+    usedevelop = true
+    envdir =
+        x86: .venv-x86
+        x64: .venv-x64
+    commands =
+
+
 Prevent symbolic links in virtualenv
 ------------------------------------
 By default virtualenv will use symlinks to point to the system's python files, modules, etc.

src/tox/config/__init__.py

@@ -1015,6 +1015,8 @@ def __init__(self, config, ini_path, ini_data):  # noqa
         self._cfg = py.iniconfig.IniConfig(config.toxinipath, ini_data)
         previous_line_of = self._cfg.lineof
 
+        self.expand_section_names(self._cfg)
+
         def line_of_default_to_zero(section, name=None):
             at = previous_line_of(section, name=name)
             if at is None:
@@ -1353,6 +1355,28 @@ def _getenvdata(self, reader, config):
             raise tox.exception.ConfigError(msg)
         return env_list, all_envs, _split_env(from_config), envlist_explicit
 
+    @staticmethod
+    def expand_section_names(config):
+        """Generative section names.
+
+        Allow writing section as [testenv:py{36,37}-cov]
+        The parser will see it as two different sections: [testenv:py36-cov], [testenv:py37-cov]
+
+        """
+        factor_re = re.compile(r"\{\s*([\w\s,]+)\s*\}")
+        split_re = re.compile(r"\s*,\s*")
+        to_remove = set()
+        for section in list(config.sections):
+            split_section = factor_re.split(section)
+            for parts in itertools.product(*map(split_re.split, split_section)):
+                section_name = "".join(parts)
+                if section_name not in config.sections:
+                    config.sections[section_name] = config.sections[section]
+                    to_remove.add(section)
+
+        for section in to_remove:
+            del config.sections[section]
+
 
 def _split_env(env):
     """if handed a list, action="append" was used for -e """

tests/unit/config/test_config.py

@@ -859,6 +859,15 @@ def test_getbool(self, newconfig):
         (msg,) = excinfo.value.args
         assert msg == "key5: boolean value 'yes' needs to be 'True' or 'False'"
 
+    def test_expand_section_name(self, newconfig):
+        config = newconfig(
+            """
+            [testenv:custom-{one,two,three}-{four,five}-six]
+        """
+        )
+        assert "testenv:custom-one-five-six" in config._cfg.sections
+        assert "testenv:custom-{one,two,three}-{four,five}-six" not in config._cfg.sections
+
 
 class TestIniParserPrefix:
     def test_basic_section_access(self, newconfig):