Implement `--executable' option (#257)

src/installer/__main__.py

@@ -31,6 +31,13 @@ def _get_main_parser() -> argparse.ArgumentParser:
         type=str,
         help="override prefix to install packages to",
     )
+    parser.add_argument(
+        "--executable",
+        metavar="path",
+        default=sys.executable,
+        type=str,
+        help="#! executable to install scripts with (default=sys.executable)",
+    )
     parser.add_argument(
         "--compile-bytecode",
         action="append",
@@ -103,7 +110,7 @@ def _main(cli_args: Sequence[str], program: Optional[str] = None) -> None:
                 source.validate_record(validate_contents=args.validate_record == "all")
             destination = SchemeDictionaryDestination(
                 scheme_dict=_get_scheme_dict(source.distribution, prefix=args.prefix),
-                interpreter=sys.executable,
+                interpreter=args.executable,
                 script_kind=get_launcher_kind(),
                 bytecode_optimization_levels=bytecode_levels,
                 destdir=args.destdir,

tests/test_main.py

@@ -74,6 +74,28 @@ def test_main_prefix(fancy_wheel, tmp_path):
     }
 
 
+def test_main_executable(fancy_wheel, tmp_path):
+    destdir = tmp_path / "dest"
+
+    main(
+        [
+            str(fancy_wheel),
+            "-d",
+            str(destdir),
+            "--executable",
+            "/monty/python3.x",
+        ],
+        "python -m installer",
+    )
+
+    installed_scripts = destdir.rglob("bin/*")
+
+    for f in installed_scripts:
+        with f.open("rb") as fp:
+            shebang = fp.readline()
+            assert shebang == b"#!/monty/python3.x\n"
+
+
 def test_main_no_pyc(fancy_wheel, tmp_path):
     destdir = tmp_path / "dest"