Make proxy parameter override environment proxy

Author: q0w

news/10685.bugfix.rst

@@ -0,0 +1 @@
+Make the ``--proxy`` parameter take precedence over environment variables.

src/pip/_internal/cli/req_command.py

@@ -148,6 +148,7 @@ def _build_session(
                 "http": options.proxy,
                 "https": options.proxy,
             }
+            session.trust_env = False
 
         # Determine if we can prompt the user for authentication or not
         session.auth.prompting = not options.no_input

tests/functional/test_proxy.py

@@ -0,0 +1,37 @@
+from typing import Any, Dict, Optional
+
+import proxy
+import pytest
+from proxy.http.proxy import HttpProxyBasePlugin
+
+from tests.lib import PipTestEnvironment
+from tests.lib.path import Path
+
+
+class AccessLogPlugin(HttpProxyBasePlugin):
+    def on_access_log(self, context: Dict[str, Any]) -> Optional[Dict[str, Any]]:
+        print(context)
+        return super().on_access_log(context)
+
+
+@pytest.mark.network
+def test_proxy_overrides_env(
+    script: PipTestEnvironment, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setenv("http_proxy", "127:0.0.1:8888")
+    monkeypatch.setenv("https_proxy", "127:0.0.1:8888")
+    with proxy.Proxy(
+        port=8899,
+    ), proxy.Proxy(plugins=[AccessLogPlugin], port=8888):
+        result = script.pip(
+            "download",
+            "--proxy",
+            "http://127.0.0.1:8899",
+            "--trusted-host",
+            "127.0.0.1",
+            "-d",
+            "pip_downloads",
+            "INITools==0.1",
+        )
+        result.did_create(Path("scratch") / "pip_downloads" / "INITools-0.1.tar.gz")
+        assert "CONNECT" not in result.stdout

tests/requirements.txt

@@ -11,3 +11,4 @@ virtualenv < 20.0
 werkzeug
 wheel
 tomli-w
+proxy.py