Removes automatic reuse of venvs when no-install is provided (wntrblm…

…#394)

Also reduces log verbosity by only noting package reinstallation
when venv is not explicitly reused.

docs/config.rst

@@ -424,6 +424,7 @@ The following options can be specified in the Noxfile:
 * ``nox.options.default_venv_backend`` is equivalent to specifying :ref:`-db or --default-venv-backend <opt-default-venv-backend>`.
 * ``nox.options.force_venv_backend`` is equivalent to specifying :ref:`-fb or --force-venv-backend <opt-force-venv-backend>`.
 * ``nox.options.reuse_existing_virtualenvs`` is equivalent to specifying :ref:`--reuse-existing-virtualenvs <opt-reuse-existing-virtualenvs>`. You can force this off by specifying ``--no-reuse-existing-virtualenvs`` during invocation.
+* ``nox.options.no_install`` is equivalent to specifying :ref:`--no-install <opt-no-install>`.
 * ``nox.options.stop_on_first_error`` is equivalent to specifying :ref:`--stop-on-first-error <opt-stop-on-first-error>`. You can force this off by specifying ``--no-stop-on-first-error`` during invocation.
 * ``nox.options.error_on_missing_interpreters`` is equivalent to specifying :ref:`--error-on-missing-interpreters <opt-error-on-missing-interpreters>`. You can force this off by specifying ``--no-error-on-missing-interpreters`` during invocation.
 * ``nox.options.error_on_external_run`` is equivalent to specifying :ref:`--error-on-external-run <opt-error-on-external-run>`. You can force this off by specifying ``--no-error-on-external-run`` during invocation.

nox/sessions.py

@@ -379,9 +379,10 @@ def conda_install(
                 )
                 return None
             else:
-                logger.info(
-                    "Venv not created yet: ignoring --no-install and installing from conda."
-                )
+                if not self._runner.global_config.reuse_existing_virtualenvs:
+                    logger.info(
+                        "Venv not created yet: ignoring --no-install and installing from conda."
+                    )
 
         # Escape args that should be (conda-specific; pip install does not need this)
         args = _dblquote_pkg_install_args(args)
@@ -450,9 +451,10 @@ def install(self, *args: str, **kwargs: Any) -> None:
                 )
                 return None
             else:
-                logger.info(
-                    "Venv not created yet: ignoring --no-install and installing."
-                )
+                if not self._runner.global_config.reuse_existing_virtualenvs:
+                    logger.info(
+                        "Venv not created yet: ignoring --no-install and installing."
+                    )
 
         if "silent" not in kwargs:
             kwargs["silent"] = True
@@ -544,9 +546,7 @@ def _create_venv(self) -> None:
             return
 
         reuse_existing = (
-            self.func.reuse_venv
-            or self.global_config.reuse_existing_virtualenvs
-            or self.global_config.no_install
+            self.func.reuse_venv or self.global_config.reuse_existing_virtualenvs
         )
 
         if backend is None or backend == "virtualenv":