fix(packages): fix local plugin installation

The most recent version of pip (23.1) removes support for the
`--install-option` parameter to `pip install`.  This breaks our
`install_local_package` function, which uses `--install-option`
because `pip install --target` didn't used to work with `pip install
--editable`.

As it turns out, recent versions of pip support the use of `--target`
with `--editable`.  So here we make use of that.

Note that this also relieves us of the need to parse our local
plugin requirements ourselves (thus, hopefully, fixing #865.)

lektor/packages.py

@@ -3,7 +3,6 @@
 import shutil
 import site
 import sys
-import tempfile
 from subprocess import PIPE
 
 import click
@@ -104,53 +103,21 @@ def download_and_install_package(
 def install_local_package(package_root, path):
     """This installs a local dependency of a package."""
     # XXX: windows
-    env = dict(os.environ)
-    env["PYTHONPATH"] = package_root
-
-    # Step 1: generate egg info and link us into the target folder.
     rv = portable_popen(
         [
             sys.executable,
             "-m",
             "pip",
             "install",
+            "--target",
+            package_root,
             "--editable",
             path,
-            "--install-option=--install-dir=%s" % package_root,
-            "--no-deps",
         ],
-        env=env,
     ).wait()
     if rv != 0:
         raise RuntimeError("Failed to install local package")
 
-    # Step 2: generate the egg info into a temp folder to find the
-    # requirements.
-    tmp = tempfile.mkdtemp()
-    try:
-        rv = portable_popen(
-            [
-                sys.executable,
-                "setup.py",
-                "--quiet",
-                "egg_info",
-                "--quiet",
-                "--egg-base",
-                tmp,
-            ],
-            cwd=path,
-        ).wait()
-        dirs = os.listdir(tmp)
-        if rv != 0 or len(dirs) != 1:
-            raise RuntimeError("Failed to create egg info for local package.")
-        requires = os.path.join(tmp, dirs[0], "requires.txt")
-
-        # We have dependencies, install them!
-        if os.path.isfile(requires):
-            download_and_install_package(package_root, requirements_file=requires)
-    finally:
-        shutil.rmtree(tmp)
-
 
 def get_package_info(path):
     """Returns the name of a package at a path."""

setup.cfg

@@ -45,11 +45,11 @@ install_requires =
     Jinja2>=3.0
     markupsafe
     mistune>=0.7.0,<2
-    pip
+    pip>=21.1
     python-slugify
     pytz
     requests
-    setuptools
+    setuptools>=45.2
     watchdog
     Werkzeug<3