Introduce pyproject.toml

Using pyproject.toml, defined in PEP518, allows us to have
an isolated build environment, ensuring that Cython can be installed
before calling setup.py in tox. This allows us to use cython helpers
in the setup.py script.

This is a prerequisite for introducing Cython in the codebase

1 files changed, 6 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index a7a4874c7..0a269c17d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,6 +4,7 @@
 [tox]
 envlist = py{35,36,37}
 skip_missing_interpreters = true
+isolated_build = true
 
 #
 # Defaults for all environments
@@ -147,3 +148,8 @@ deps =
     -rrequirements/requirements.txt
     -rrequirements/dev-requirements.txt
     -rrequirements/plugin-requirements.txt
+
+# When building using PEP518 and 517, we don't want default dependencies
+# installed by the base environment.
+[testenv:.package]
+deps =