Merge ~pappacena/turnip:make-target-py3-check into turnip:master

[Thiago F. Pappacena]

Adding Makefile rule to run `make check-python-compat` and run tests on both python 2 and python 3 envs.

[Colin Watson (cjwatson)]

review: Needs Information

1a866e1... by Thiago F. Pappacena on 2020-05-13

Keeping python2 and python3 envs simultaneously

[Thiago F. Pappacena (pappacena)]

cjwatson, pushed the changes to keep both venvs at the same time. Let me know if you would like to review that.

75589bf... by Thiago F. Pappacena on 2020-05-13

Merge branch 'master' into make-target-py3-check

[Colin Watson (cjwatson)]

review: Approve

ed898b0... by Thiago F. Pappacena on 2020-05-14

Preventing environment variables from overriding some Makefile vars

diff --git a/.gitignore b/.gitignore
index fb9d39c..5698ab9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ dist
 download-cache
 eggs
 env
+py3env
 pip-cache
 *.egg*
 *.egg-info
diff --git a/Makefile b/Makefile
index c514366..9e6bb12 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,7 @@
 # GNU Affero General Public License version 3 (see the file LICENSE).
 
 ENV := $(CURDIR)/env
+PY3_ENV := $(CURDIR)/py3env
 PIP_CACHE = $(CURDIR)/pip-cache
 
 PYTHON := $(ENV)/bin/python
@@ -11,6 +12,7 @@ PIP := $(ENV)/bin/pip
 VIRTUALENV := virtualenv
 
 DEPENDENCIES_URL := https://git.launchpad.net/~canonical-launchpad-branches/turnip/+git/dependencies
+PIP_SOURCE_DIR := dependencies
 
 PIP_ARGS ?= --quiet
 ifneq ($(PIP_SOURCE_DIR),)
@@ -59,7 +61,7 @@ test: $(ENV)
 
 clean:
 	find turnip -name '*.py[co]' -exec rm '{}' \;
-	rm -rf $(ENV) $(PIP_CACHE)
+	rm -rf $(ENV) $(PY3_ENV) $(PIP_CACHE)
 	rm -f turnip/version_info.py
 
 dist:
@@ -80,6 +82,11 @@ pip-check: $(ENV)
 
 check: pip-check test lint
 
+check-python3:
+	$(MAKE) check VENV_ARGS="-p python3" ENV="$(PY3_ENV)"
+
+check-python-compat: check check-python3
+
 run-api: $(ENV)
 	$(PSERVE) api.ini --reload