pip installer: fix installed script executable

poetry/utils/pip.py

+import os
+import sys
+
 from pathlib import Path
 from pathlib import Path
 from typing import Union
 from typing import Union
 
 
 from poetry.exceptions import PoetryException
 from poetry.exceptions import PoetryException
 from poetry.utils.env import Env
 from poetry.utils.env import Env
+from poetry.utils.env import EnvCommandError
 from poetry.utils.env import ephemeral_environment
 from poetry.utils.env import ephemeral_environment
 
 
 
 
@@ -14,9 +18,13 @@ def pip_install(
     upgrade: bool = False,
     upgrade: bool = False,
 ) -> Union[int, str]:
 ) -> Union[int, str]:
     path = Path(path) if isinstance(path, str) else path
     path = Path(path) if isinstance(path, str) else path
+    is_wheel = path.suffix == ".whl"
 
 
     args = ["install", "--prefix", str(environment.path)]
     args = ["install", "--prefix", str(environment.path)]
 
 
+    if not is_wheel:
+        args.insert(1, "--use-pep517")
+
     if upgrade:
     if upgrade:
         args.append("--upgrade")
         args.append("--upgrade")
 
 
@@ -32,16 +40,21 @@ def pip_install(
 
 
     args.append(str(path))
     args.append(str(path))
 
 
-    if path.is_file() and path.suffix == ".whl":
+    try:
         return environment.run_pip(*args)
         return environment.run_pip(*args)
-
+    except EnvCommandError as e:
+        if sys.version_info < (3, 7) and not is_wheel:
+            # Under certain Python3.6 installs vendored pip wheel does not contain zip-safe
+            # pep517 lib. In this cases we create an isolated ephemeral virtual environment.
             with ephemeral_environment(
             with ephemeral_environment(
                 executable=environment.python, pip=True, setuptools=True
                 executable=environment.python, pip=True, setuptools=True
             ) as env:
             ) as env:
-        return env.run(
-            "pip",
+                return environment.run(
+                    env._bin("pip"),
                     *args,
                     *args,
+                    env={**os.environ, "PYTHONPATH": str(env.purelib)},
                 )
                 )
+        raise PoetryException(f"Failed to install {path.as_posix()}") from e
 
 
 
 
 def pip_editable_install(directory: Path, environment: Env) -> Union[int, str]:
 def pip_editable_install(directory: Path, environment: Env) -> Union[int, str]:

tests/installation/test_executor.py

@@ -137,7 +137,7 @@ Package operations: 4 installs, 1 update, 1 removal
     expected = set(expected.splitlines())
     expected = set(expected.splitlines())
     output = set(io.fetch_output().splitlines())
     output = set(io.fetch_output().splitlines())
     assert expected == output
     assert expected == output
-    assert 4 == len(env.executed)
+    assert 5 == len(env.executed)
     assert 0 == return_code
     assert 0 == return_code
     pip_editable_install.assert_called_once()
     pip_editable_install.assert_called_once()