mkvenv: work around broken pip installations on Debian 10

This is a workaround intended for Debian 10, where the debian-patched
pip does not function correctly if accessed from within a virtual
environment.

We don't support Debian 10 as a build platform any longer, though we do
still utilize it for our build-tricore-softmmu CI test. It's also
possible that this bug might appear on other derivative platforms and
this workaround may prove useful.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20230511035435.734312-11-jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

python/scripts/mkvenv.py

@@ -161,7 +161,7 @@ class QemuEnvBuilder(venv.EnvBuilder):
             ):
                 kwargs["with_pip"] = False
             else:
-                check_ensurepip()
+                check_ensurepip(suggest_remedy=True)
 
         super().__init__(*args, **kwargs)
 
@@ -266,7 +266,7 @@ def need_ensurepip() -> bool:
     return True
 
 
-def check_ensurepip() -> None:
+def check_ensurepip(prefix: str = "", suggest_remedy: bool = False) -> None:
     """
     Check that we have ensurepip.
 
@@ -277,12 +277,15 @@ def check_ensurepip() -> None:
             "Python's ensurepip module is not found.\n"
             "It's normally part of the Python standard library, "
             "maybe your distribution packages it separately?\n"
-            "Either install ensurepip, or alleviate the need for it in the "
-            "first place by installing pip and setuptools for "
-            f"'{sys.executable}'.\n"
-            "(Hint: Debian puts ensurepip in its python3-venv package.)"
+            "(Debian puts ensurepip in its python3-venv package.)\n"
         )
-        raise Ouch(msg)
+        if suggest_remedy:
+            msg += (
+                "Either install ensurepip, or alleviate the need for it in the"
+                " first place by installing pip and setuptools for "
+                f"'{sys.executable}'.\n"
+            )
+        raise Ouch(prefix + msg)
 
     # ensurepip uses pyexpat, which can also go missing on us:
     if not find_spec("pyexpat"):
@@ -290,12 +293,15 @@ def check_ensurepip() -> None:
             "Python's pyexpat module is not found.\n"
             "It's normally part of the Python standard library, "
             "maybe your distribution packages it separately?\n"
-            "Either install pyexpat, or alleviate the need for it in the "
-            "first place by installing pip and setuptools for "
-            f"'{sys.executable}'.\n\n"
-            "(Hint: NetBSD's pkgsrc debundles this to e.g. 'py310-expat'.)"
+            "(NetBSD's pkgsrc debundles this to e.g. 'py310-expat'.)\n"
         )
-        raise Ouch(msg)
+        if suggest_remedy:
+            msg += (
+                "Either install pyexpat, or alleviate the need for it in the "
+                "first place by installing pip and setuptools for "
+                f"'{sys.executable}'.\n"
+            )
+        raise Ouch(prefix + msg)
 
 
 def make_venv(  # pylint: disable=too-many-arguments
@@ -501,6 +507,38 @@ def generate_console_scripts(
             logger.debug("wrote console_script '%s'", filename)
 
 
+def checkpip() -> bool:
+    """
+    Debian10 has a pip that's broken when used inside of a virtual environment.
+
+    We try to detect and correct that case here.
+    """
+    try:
+        # pylint: disable=import-outside-toplevel,unused-import,import-error
+        # pylint: disable=redefined-outer-name
+        import pip._internal  # type: ignore  # noqa: F401
+
+        logger.debug("pip appears to be working correctly.")
+        return False
+    except ModuleNotFoundError as exc:
+        if exc.name == "pip._internal":
+            # Uh, fair enough. They did say "internal".
+            # Let's just assume it's fine.
+            return False
+        logger.warning("pip appears to be malfunctioning: %s", str(exc))
+
+    check_ensurepip("pip appears to be non-functional, and ")
+
+    logger.debug("Attempting to repair pip ...")
+    subprocess.run(
+        (sys.executable, "-m", "ensurepip"),
+        stdout=subprocess.DEVNULL,
+        check=True,
+    )
+    logger.debug("Pip is now (hopefully) repaired!")
+    return True
+
+
 def pkgname_from_depspec(dep_spec: str) -> str:
     """
     Parse package name out of a PEP-508 depspec.
@@ -741,10 +779,12 @@ def post_venv_setup() -> None:
     This is intended to be run *inside the venv* after it is created.
     """
     logger.debug("post_venv_setup()")
-    # Generate a 'pip' script so the venv is usable in a normal
-    # way from the CLI. This only happens when we inherited pip from a
-    # parent/system-site and haven't run ensurepip in some way.
-    generate_console_scripts(["pip"])
+    # Test for a broken pip (Debian 10 or derivative?) and fix it if needed
+    if not checkpip():
+        # Finally, generate a 'pip' script so the venv is usable in a normal
+        # way from the CLI. This only happens when we inherited pip from a
+        # parent/system-site and haven't run ensurepip in some way.
+        generate_console_scripts(["pip"])
 
 
 def _add_create_subcommand(subparsers: Any) -> None: