Add seasion.create_tmp (#320)

* Address #319: Give a create_tmp API

* more stuff

* fade to black

* woops

* calculate tmp directly from envdir

* cleanup and fix tests

nox/sessions.py

@@ -135,6 +135,13 @@ def bin(self) -> Optional[str]:
         """The bin directory for the virtualenv."""
         return self.virtualenv.bin
 
+    def create_tmp(self) -> str:
+        """Create, and return, a temporary directory."""
+        tmpdir = os.path.join(self._runner.envdir, "tmp")
+        os.makedirs(tmpdir, exist_ok=True)
+        self.env["TMPDIR"] = tmpdir
+        return tmpdir
+
     @property
     def interactive(self) -> bool:
         """Returns True if Nox is being run in an interactive session or False otherwise."""
@@ -388,33 +395,36 @@ def __str__(self) -> str:
     def friendly_name(self) -> str:
         return self.signatures[0] if self.signatures else self.name
 
+    @property
+    def envdir(self) -> str:
+        return _normalize_path(self.global_config.envdir, self.friendly_name)
+
     def _create_venv(self) -> None:
         if self.func.python is False:
             self.venv = ProcessEnv()
             return
 
-        path = _normalize_path(self.global_config.envdir, self.friendly_name)
         reuse_existing = (
             self.func.reuse_venv or self.global_config.reuse_existing_virtualenvs
         )
 
         if not self.func.venv_backend or self.func.venv_backend == "virtualenv":
             self.venv = VirtualEnv(
-                path,
+                self.envdir,
                 interpreter=self.func.python,  # type: ignore
                 reuse_existing=reuse_existing,
                 venv_params=self.func.venv_params,
             )
         elif self.func.venv_backend == "conda":
             self.venv = CondaEnv(
-                path,
+                self.envdir,
                 interpreter=self.func.python,  # type: ignore
                 reuse_existing=reuse_existing,
                 venv_params=self.func.venv_params,
             )
         elif self.func.venv_backend == "venv":
             self.venv = VirtualEnv(
-                path,
+                self.envdir,
                 interpreter=self.func.python,  # type: ignore
                 reuse_existing=reuse_existing,
                 venv=True,

noxfile.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import functools
 import os
 
 import nox
@@ -30,6 +31,7 @@ def is_python_version(session, version):
 @nox.session(python=["3.5", "3.6", "3.7", "3.8"])
 def tests(session):
     """Run test suite with pytest."""
+    session.create_tmp()
     session.install("-r", "requirements-test.txt")
     session.install("-e", ".[tox_to_nox]")
     tests = session.posargs or ["tests/"]
@@ -45,6 +47,7 @@ def tests(session):
 @nox.session(python=["3.5", "3.6", "3.7", "3.8"], venv_backend="conda")
 def conda_tests(session):
     """Run test suite with pytest."""
+    session.create_tmp()
     session.conda_install(
         "--file", "requirements-conda-test.txt", "--channel", "conda-forge"
     )
@@ -93,11 +96,15 @@ def lint(session):
 @nox.session(python="3.8")
 def docs(session):
     """Build the documentation."""
-    session.run("rm", "-rf", "docs/_build", external=True)
+    output_dir = os.path.join(session.create_tmp(), "output")
+    doctrees, html = map(
+        functools.partial(os.path.join, output_dir), ["doctrees", "html"]
+    )
+    session.run("rm", "-rf", output_dir, external=True)
     session.install("-r", "requirements-test.txt")
     session.install(".")
     session.cd("docs")
-    sphinx_args = ["-b", "html", "-W", "-d", "_build/doctrees", ".", "_build/html"]
+    sphinx_args = ["-b", "html", "-W", "-d", doctrees, ".", html]
 
     if not session.interactive:
         sphinx_cmd = "sphinx-build"

tests/test_sessions.py

@@ -16,6 +16,7 @@
 import logging
 import os
 import sys
+import tempfile
 from unittest import mock
 
 import nox.command
@@ -74,6 +75,24 @@ def make_session_and_runner(self):
         runner.venv.bin = "/no/bin/for/you"
         return nox.sessions.Session(runner=runner), runner
 
+    def test_create_tmp(self):
+        session, runner = self.make_session_and_runner()
+        with tempfile.TemporaryDirectory() as root:
+            runner.global_config.envdir = root
+            tmpdir = session.create_tmp()
+            assert session.env["TMPDIR"] == tmpdir
+            assert tmpdir.startswith(root)
+
+    def test_create_tmp_twice(self):
+        session, runner = self.make_session_and_runner()
+        with tempfile.TemporaryDirectory() as root:
+            runner.global_config.envdir = root
+            runner.venv.bin = bin
+            session.create_tmp()
+            tmpdir = session.create_tmp()
+            assert session.env["TMPDIR"] == tmpdir
+            assert tmpdir.startswith(root)
+
     def test_properties(self):
         session, runner = self.make_session_and_runner()