config: add support for installer.parallel

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

Resolves: #3087

Author: abn

docs/docs/configuration.md

@@ -102,6 +102,15 @@ 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.

poetry/config/config.py

@@ -38,6 +38,7 @@ class Config(object):
             "path": os.path.join("{cache-dir}", "virtualenvs"),
         },
         "experimental": {"new-installer": True},
+        "installer": {"parallel": True},
     }
 
     def __init__(
@@ -131,14 +132,22 @@ def process(self, value):  # type: (Any) -> Any
         return re.sub(r"{(.+?)}", lambda m: self.get(m.group(1)), value)
 
     def _get_validator(self, name):  # type: (str) -> Callable
-        if name in {"virtualenvs.create", "virtualenvs.in-project"}:
+        if name in {
+            "virtualenvs.create",
+            "virtualenvs.in-project",
+            "installer.parallel",
+        }:
             return boolean_validator
 
         if name == "virtualenvs.path":
             return str
 
     def _get_normalizer(self, name):  # type: (str) -> Callable
-        if name in {"virtualenvs.create", "virtualenvs.in-project"}:
+        if name in {
+            "virtualenvs.create",
+            "virtualenvs.in-project",
+            "installer.parallel",
+        }:
             return boolean_normalizer
 
         if name == "virtualenvs.path":

poetry/console/commands/config.py

@@ -63,6 +63,7 @@ def unique_config_values(self):
                 boolean_normalizer,
                 True,
             ),
+            "installer.parallel": (boolean_validator, boolean_normalizer, True,),
         }
 
         return unique_config_values

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

tests/console/commands/test_config.py

@@ -5,6 +5,8 @@
 
 from poetry.config.config_source import ConfigSource
 from poetry.factory import Factory
+from poetry.utils._compat import PY2
+from poetry.utils._compat import WINDOWS
 
 
 @pytest.fixture()
@@ -17,6 +19,7 @@ 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.path = {path}  # /foo{sep}virtualenvs
@@ -34,6 +37,7 @@ 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.path = {path}  # /foo{sep}virtualenvs
@@ -73,6 +77,7 @@ 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.path = {path}  # /foo{sep}virtualenvs
@@ -108,3 +113,25 @@ 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"]
+
+
+@pytest.mark.skipif(
+    PY2 and WINDOWS, reason="Python 2.7 under windows is enforced serial"
+)
+def test_config_installer_parallel(tester, command_tester_factory):
+    tester.execute("--local installer.parallel")
+    assert tester.io.fetch_output().strip() == "true"
+
+    assert (
+        command_tester_factory("install")._command._installer._executor._max_workers > 1
+    )
+
+    tester.io.clear_output()
+    tester.execute("--local installer.parallel false")
+    tester.execute("--local installer.parallel")
+    assert tester.io.fetch_output().strip() == "false"
+
+    assert (
+        command_tester_factory("install")._command._installer._executor._max_workers
+        == 1
+    )