config: add support for installer.parallel

This change allows users to disable parallel execution while using the
new installer.

Resolves: #3087

Author: abn

Diff for: docs/docs/configuration.md

@@ -103,6 +103,15 @@ Defaults to one of the following directories:
 - Windows: `C:\Users\<username>\AppData\Local\pypoetry\Cache`
 - Unix:    `~/.cache/pypoetry`
 
+### `installer.parallel`: boolean
+
+Use parallel execution when using the new (`>=1.1.0`) installer.
+Defaults to `true`.
+
+!!!note:
+        This configuration will be ignored, and parallel execution disabled when running
+        Python 2.7 under Windows.
+
 ### `virtualenvs.create`: boolean
 
 Create a new virtual environment if one doesn't already exist.

Diff for: poetry/config/config.py

@@ -39,6 +39,7 @@ class Config(object):
             "options": {"always-copy": False},
         },
         "experimental": {"new-installer": True},
+        "installer": {"parallel": True},
     }
 
     def __init__(
@@ -140,6 +141,7 @@ def _get_validator(self, name):  # type: (str) -> Callable
             "virtualenvs.create",
             "virtualenvs.in-project",
             "virtualenvs.options.always-copy",
+            "installer.parallel",
         }:
             return boolean_validator
 
@@ -151,6 +153,7 @@ def _get_normalizer(self, name):  # type: (str) -> Callable
             "virtualenvs.create",
             "virtualenvs.in-project",
             "virtualenvs.options.always-copy",
+            "installer.parallel",
         }:
             return boolean_normalizer
 

Diff for: poetry/console/commands/config.py

@@ -69,6 +69,7 @@ def unique_config_values(self):
                 boolean_normalizer,
                 False,
             ),
+            "installer.parallel": (boolean_validator, boolean_normalizer, True,),
         }
 
         return unique_config_values

Diff for: poetry/installation/executor.py

@@ -32,7 +32,7 @@
 
 
 class Executor(object):
-    def __init__(self, env, pool, config, io, parallel=True):
+    def __init__(self, env, pool, config, io, parallel=None):
         self._env = env
         self._io = io
         self._dry_run = False
@@ -42,6 +42,9 @@ def __init__(self, env, pool, config, io, parallel=True):
         self._chef = Chef(config, self._env)
         self._chooser = Chooser(pool, self._env)
 
+        if parallel is None:
+            parallel = config.get("installer.parallel", True)
+
         if parallel and not (PY2 and WINDOWS):
             # This should be directly handled by ThreadPoolExecutor
             # however, on some systems the number of CPUs cannot be determined

Diff for: tests/config/test_config.py

@@ -1,16 +1,29 @@
 import os
 
+import pytest
 
-def test_config_get_default_value(config):
-    assert config.get("virtualenvs.create") is True
+
+@pytest.mark.parametrize(
+    ("name", "value"), [("installer.parallel", True), ("virtualenvs.create", True)]
+)
+def test_config_get_default_value(config, name, value):
+    assert config.get(name) is value
 
 
 def test_config_get_processes_depended_on_values(config):
     assert os.path.join("/foo", "virtualenvs") == config.get("virtualenvs.path")
 
 
-def test_config_get_from_environment_variable(config, environ):
-    assert config.get("virtualenvs.create")
-
-    os.environ["POETRY_VIRTUALENVS_CREATE"] = "false"
-    assert not config.get("virtualenvs.create")
+@pytest.mark.parametrize(
+    ("name", "env_value", "value"),
+    [
+        ("installer.parallel", "true", True),
+        ("installer.parallel", "false", False),
+        ("virtualenvs.create", "true", True),
+        ("virtualenvs.create", "false", False),
+    ],
+)
+def test_config_get_from_environment_variable(config, environ, name, env_value, value):
+    env_var = "POETRY_{}".format("_".join(k.upper() for k in name.split(".")))
+    os.environ[env_var] = env_value
+    assert config.get(name) is value

Diff for: tests/console/commands/test_config.py

@@ -6,6 +6,8 @@
 from poetry.config.config_source import ConfigSource
 from poetry.core.pyproject import PyProjectException
 from poetry.factory import Factory
+from poetry.utils._compat import PY2
+from poetry.utils._compat import WINDOWS
 
 
 @pytest.fixture()
@@ -28,6 +30,7 @@ def test_list_displays_default_value_if_not_set(tester, config):
 
     expected = """cache-dir = "/foo"
 experimental.new-installer = true
+installer.parallel = true
 virtualenvs.create = true
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
@@ -46,6 +49,7 @@ def test_list_displays_set_get_setting(tester, config):
 
     expected = """cache-dir = "/foo"
 experimental.new-installer = true
+installer.parallel = true
 virtualenvs.create = false
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
@@ -86,6 +90,7 @@ def test_list_displays_set_get_local_setting(tester, config):
 
     expected = """cache-dir = "/foo"
 experimental.new-installer = true
+installer.parallel = true
 virtualenvs.create = false
 virtualenvs.in-project = null
 virtualenvs.options.always-copy = false
@@ -122,3 +127,25 @@ def test_set_cert(tester, auth_config_source, mocker):
     tester.execute("certificates.foo.cert path/to/ca.pem")
 
     assert "path/to/ca.pem" == auth_config_source.config["certificates"]["foo"]["cert"]
+
+
+def test_config_installer_parallel(tester, command_tester_factory):
+    serial_enforced = PY2 and WINDOWS
+
+    tester.execute("--local installer.parallel")
+    assert tester.io.fetch_output().strip() == "true"
+
+    workers = command_tester_factory(
+        "install"
+    )._command._installer._executor._max_workers
+    assert workers > 1 or (serial_enforced and workers == 1)
+
+    tester.io.clear_output()
+    tester.execute("--local installer.parallel false")
+    tester.execute("--local installer.parallel")
+    assert tester.io.fetch_output().strip() == "false"
+
+    workers = command_tester_factory(
+        "install"
+    )._command._installer._executor._max_workers
+    assert workers == 1