pip 10 and pyproject.toml is required for wheel build

changelog/850.feature.rst

@@ -1 +1 @@
-PEP-518 support: provide a tox configuration flag ``build`` which can be either ``sdist`` or ``wheel``. For ``sdist`` (default) we build the package as before by using ``python setup.py sdist``. However, when ``wheel`` is enabled now we'll use ``pip wheel`` to build it, and we'll also install wheels in these case into the environments. Note: ``pip`` 10 supports specifying project dependencies (such as ``setuptools-scm``, or a given ``setuptools`` version) via ``pyproject.toml``. Once ``pip`` supports building ``sdist`` to we'll migrate over the ``sdist`` build too. @gaborbernat
+PEP-518 support: provide a tox configuration flag ``build`` which can be either ``sdist`` or ``wheel``. For ``sdist`` (default) we build the package as before by using ``python setup.py sdist``. However, when ``wheel`` is enabled now we'll use ``pip wheel`` to build it, and we'll also install wheels in these case into the environments. Note: ``pip`` 10 supports specifying project dependencies (such as ``setuptools-scm``, or a given ``setuptools`` version) via ``pyproject.toml``. Once ``pip`` supports building ``sdist`` to we'll migrate over the ``sdist`` build too.`@gaborbernat <https://github.com/gaborbernat>`_

changelog/851.feature.rst

@@ -1 +1 @@
-While running tox invokes various commands (such as building the package, pip installing dependencies and so on), these were printed in case they failed as Python arrays. Changed the representation to a shell command, allowing the users to quickly replicate/debug the failure on their own. @gaborbernat
+While running tox invokes various commands (such as building the package, pip installing dependencies and so on), these were printed in case they failed as Python arrays. Changed the representation to a shell command, allowing the users to quickly replicate/debug the failure on their own.`@gaborbernat <https://github.com/gaborbernat>`_

doc/config.rst

@@ -91,6 +91,11 @@ and will first lookup global tox settings in this section:
 
             pip wheel . --no-dep
 
+        .. note::
+
+           wheel should only be used with pip ``10+`` and a ``pyproject.toml``, the build will
+           fail if either is missing
+
 
     **Default:** ``sdist``
 

src/tox/session.py

@@ -15,6 +15,7 @@
 import time
 
 import py
+from pkg_resources import get_distribution
 
 import tox
 from tox._verlib import IrrationalVersionError, NormalizedVersion
@@ -492,6 +493,15 @@ def _make_package(self, action, setup):
                 cwd=self.config.setupdir,
             )
         elif self.config.build == "wheel":
+            if NormalizedVersion(get_distribution("pip").version).parts[0][0] > 10:
+                raise RuntimeError("wheel support requires pip 10 or later")
+            py_project_toml = self.config.setupdir.join("pyproject.toml")
+            if not py_project_toml.exists():
+                raise RuntimeError(
+                    "wheel support requires creating and setting build-requires in {}".format(
+                        py_project_toml
+                    )
+                )
             action.popen(
                 [
                     sys.executable,