Fix problems when using horse-with-no-namespace with zc.buildout.

1. Buildout recipes are loaded via a pkg_resources API that updates sys.path. We have to make sure that the __path__ for a namespace module gets updated when sys.path changes.
2. Scripts installed by buildout do their own mangling of sys.path. We have to make sure that the pkg_resources working set doesn't get initialized until after that.

Author: davisagli

demo_buildout/.gitignore

@@ -0,0 +1,7 @@
+/.installed.cfg
+/.venv
+/bin
+/develop-eggs
+/eggs
+/parts
+/var

demo_buildout/Makefile

@@ -1,13 +1,17 @@
 .PHONY: all
-all: bin/py
-	bin/py test.py
+all: bin/instance
+	bin/instance run test.py
 
-bin/py: .venv/bin/buildout
-	.venv/bin/buildout
+bin/instance: .venv/bin/buildout
+	.venv/bin/buildout -D
 
 .venv/bin/pip:
-	python3 -m venv .venv
+	uv venv --seed .venv
 
 .venv/bin/buildout: .venv/bin/pip
-	.venv/bin/pip install -r https://dist.plone.org/release/6.1-latest/requirements.txt
+	.venv/bin/pip install -r requirements.txt
 	.venv/bin/pip install -e ..
+
+.PHONY: clean
+clean:
+	rm -rf .installed.cfg .venv bin develop-eggs eggs parts var

demo_buildout/buildout.cfg

@@ -1,19 +1,19 @@
 [buildout]
 extends =
-    https://dist.plone.org/release/6.1-latest/versions.cfg
-    https://dist.plone.org/release/6.1-latest/versions-ecosystem.cfg
-    https://dist.plone.org/release/6.1-latest/versions-extra.cfg
+    https://dist.plone.org/release/6.1.2/versions.cfg
+
 parts =
-    py
-show-picked-versions = true
-newest = false
+    instance
+    test
 
-[py]
-recipe = zc.recipe.egg
-interpreter = py
 eggs =
-    five.localsitemanager
-    five.globalrequest
+    Plone
+
+[instance]
+recipe = plone.recipe.zope2instance
+user = admin:admin
+eggs = ${buildout:eggs}
 
-[versions]
-five.globalrequest = 99.1
+[test]
+recipe = zc.recipe.testrunner
+eggs = ${buildout:eggs}

demo_buildout/constraints.txt

@@ -0,0 +1 @@
+-r https://dist.plone.org/release/6.1.2/requirements.txt

demo_buildout/requirements.txt

@@ -0,0 +1,5 @@
+-c constraints.txt
+
+zc.buildout
+wheel
+horse-with-no-namespace

demo_buildout/test.py

@@ -1,9 +1,9 @@
-import five.globalrequest  # noqa: F401
-import five.localsitemanager  # noqa: F401
+import zc.buildout  # noqa: F401
+import zc.lockfile  # noqa: F401
 
 print("")
-print("Testing five.globalrequest and five.localsitemanager imports...")
+print("Testing imports...")
 print("")
 
-print(five.globalrequest)
-print(five.localsitemanager)
+print(zc.buildout)
+print(zc.lockfile)

src/horse_with_no_namespace/__about__.py

@@ -1,4 +1,4 @@
 # SPDX-FileCopyrightText: 2025 David Glick <[email protected]>
 #
 # SPDX-License-Identifier: MIT
-__version__ = "20250626.0"
+__version__ = "20250704.0"

src/horse_with_no_namespace/__init__.py

@@ -12,10 +12,12 @@
 # but the site module sorts the files before processing them,
 # and that hasn't changed recently.)
 
-import pkgutil
+import importlib
 import sys
 
 logged = False
+BOLD = "\033[1m"
+RESET = "\033[0m"
 
 
 def apply():
@@ -25,37 +27,26 @@ def apply():
     global logged
     if not logged:
         print(
-            "🐎 This Python uses horse-with-no-namespace "
-            "to make pkg_resources namespace packages compatible "
-            "with PEP 420 namespace packages.",
+            f"🐎 This Python ({BOLD}{sys.executable}{RESET}) uses "
+            "horse-with-no-namespace to make pkg_resources namespace "
+            "packages compatible with PEP 420 namespace packages.",
             file=sys.stderr,
         )
         logged = True
 
-    # Only patch pkg_resources if it is installed...
-    # (To do: at some point pkg_resources will be removed from setuptools.
-    # Then we might have to add our own fake module.)
-    try:
-        import pkg_resources
-    except ImportError:
-        pass
-    else:
-        # Patch pkg_resources.declare_namespace
-        # to update __path__ using pkgutil.extend_path instead
-        def declare_namespace(packageName):
-            parent_locals = sys._getframe(1).f_locals
-            # Sometimes declare_namespace is called from pkg_resources itself;
-            # then there is no __path__ which needs to be updated.
-            if "__path__" in parent_locals:
-                parent_locals["__path__"] = pkgutil.extend_path(
-                    parent_locals["__path__"], packageName
-                )
-
-        pkg_resources.declare_namespace = declare_namespace
-
     # Remove existing namespace package modules that were already created
     # by other .pth files, possibly with an incomplete __path__
     for name, module in list(sys.modules.items()):
         loader = getattr(module, "__loader__", None)
         if loader and loader.__class__.__name__ == "NamespaceLoader":
             del sys.modules[name]
+
+    # We want to patch pkg_resources.declare_namespace,
+    # but we don't want to import it too early,
+    # because that would initialize the pkg_resources working set
+    # before sys.path is finalized.
+    # So, let's put a fake pkg_resources module is sys.modules,
+    # which will replace itself once it is accessed.
+    sys.modules["pkg_resources"] = importlib.import_module(
+        "horse_with_no_namespace.pkg_resources"
+    )

src/horse_with_no_namespace/pkg_resources.py

@@ -0,0 +1,64 @@
+import pkgutil
+import sys
+
+
+def declare_namespace(packageName):
+    # We'll patch pkg_resources to replace its declare_namespace function.
+    # The replacement bypasses all the pkg_resources namespace package
+    # machinery, and instead makes the calling module's __path__
+    # get dynamically looked up using pkgutil.extend_path.
+
+    # Get the locals from our caller
+    parent_locals = sys._getframe(1).f_locals
+
+    # Sometimes declare_namespace is called from pkg_resources itself;
+    # then there is no __path__ which needs to be updated.
+    if "__path__" not in parent_locals:
+        return
+
+    orig_path = parent_locals["__path__"]
+    del parent_locals["__path__"]
+    if "__getattr__" in parent_locals:
+        # The module already has its own __getattr__;
+        # there's nothing we can do.
+        return
+
+    # Get the module __path__ dynamically.
+    # (We can't just set it to a static value,
+    # because it needs to handle updates to sys.path)
+    def __getattr__(name):
+        if name == "__path__":
+            return pkgutil.extend_path(orig_path, packageName)
+        raise AttributeError(name)
+
+    parent_locals["__getattr__"] = __getattr__
+
+
+# The rest of this is to replace this module
+# with the real pkg_resources once it is accessed.
+
+_pkg_resources = None
+
+
+def _lazy_load_pkg_resources():
+    global _pkg_resources
+    if _pkg_resources is not None:
+        return
+    # This is called when something from pkg_resources is accessed.
+    # We import it here to avoid importing it at the top of the file,
+    # which would cause a circular import.
+    del sys.modules["pkg_resources"]
+    import pkg_resources
+
+    pkg_resources.declare_namespace = declare_namespace
+    _pkg_resources = pkg_resources
+
+
+def __getattr__(name):
+    _lazy_load_pkg_resources()
+    return getattr(_pkg_resources, name)
+
+
+def __dir__():
+    _lazy_load_pkg_resources()
+    return dir(_pkg_resources)