Add preservation of site-packages directories on upgrade.

src/manage/commands.py

@@ -254,6 +254,7 @@ def execute(self):
         "enable_shortcut_kinds": (str, config_split_append),
         "disable_shortcut_kinds": (str, config_split_append),
         "default_install_tag": (str, None),
+        "preserve_site_on_upgrade": (config_bool, None),
     },
 
     "first_run": {
@@ -794,6 +795,7 @@ class InstallCommand(BaseCommand):
     enable_shortcut_kinds = None
     disable_shortcut_kinds = None
     default_install_tag = None
+    preserve_site_on_upgrade = True
 
     def __init__(self, args, root=None):
         super().__init__(args, root)

src/manage/install_command.py

@@ -458,6 +458,86 @@ def _download_one(cmd, source, install, download_dir, *, must_copy=False):
     return package
 
 
+def _preserve_site(cmd, root):
+    if not root.is_dir():
+        return None
+    if not cmd.preserve_site_on_upgrade:
+        LOGGER.verbose("Not preserving site directory because of config")
+        return None
+    if cmd.force:
+        LOGGER.verbose("Not preserving site directory because of --force")
+        return None
+    if cmd.repair:
+        LOGGER.verbose("Not preserving site directory because of --repair")
+        return None
+    state = []
+    i = 0
+    dirs = [root]
+    root = root.with_name(f"_{root.name}")
+    root.mkdir(parents=True, exist_ok=True)
+    while dirs:
+        if dirs[0].match("site-packages"):
+            while True:
+                target = root / str(i)
+                i += 1
+                try:
+                    unlink(target)
+                    break
+                except FileNotFoundError:
+                    break
+                except OSError:
+                    LOGGER.verbose("Failed to remove %s.", target)
+            LOGGER.info("Preserving %s during update as %s.", dirs[0], target)
+            try:
+                dirs[0].rename(target)
+            except OSError:
+                LOGGER.warn("Failed to preserve %s during update.", dirs[0])
+                LOGGER.verbose("TRACEBACK", exc_info=True)
+            else:
+                state.append((dirs[0], target))
+        else:
+            dirs.extend(d for d in dirs[0].iterdir() if d.is_dir())
+        dirs.pop(0)
+    # Append None, root last so that root gets cleaned up after restore is done
+    state.append((None, root))
+    return state
+
+
+def _restore_site(cmd, state):
+    if not state:
+        return
+    for dest, src in state:
+        if not dest:
+            LOGGER.verbose("Removing preserved directory at %s", src)
+            try:
+                rmtree(
+                    src,
+                    "Removing temporary files is taking some time. " +
+                    "You can continue to wait or press Ctrl+C to abort. " +
+                    "Python has been installed, but some harmless temporary " +
+                    "files may remain on disk."
+                )
+            except KeyboardInterrupt:
+                break
+            continue
+        LOGGER.info("Restoring %s from %s after update.", dest, src)
+        try:
+            for i in src.iterdir():
+                if not i.is_dir() and not i.is_file():
+                    LOGGER.verbose("Not restoring %s because it is not a " +
+                                   "normal file or directory.", i)
+                d = dest / i.name
+                if d.exists():
+                    LOGGER.verbose("Not restoring %s because %s exists", i, d)
+                    continue
+                LOGGER.verbose("Restoring %s to %s", i, d)
+                d.parent.mkdir(parents=True, exist_ok=True)
+                i.rename(d)
+        except OSError:
+            LOGGER.warn("Failed to restore %s during update.", dest)
+            LOGGER.verbose("TRACEBACK", exc_info=True)
+
+
 def _install_one(cmd, source, install, *, target=None):
     if cmd.repair:
         LOGGER.info("Repairing %s.", install['display-name'])
@@ -475,6 +555,8 @@ def _install_one(cmd, source, install, *, target=None):
 
     dest = target or (cmd.install_dir / install["id"])
 
+    preserved_site = _preserve_site(cmd, dest)
+
     LOGGER.verbose("Extracting %s to %s", package, dest)
     if not cmd.repair:
         try:
@@ -544,6 +626,8 @@ def _install_one(cmd, source, install, *, target=None):
         with open(dest / "__install__.json", "w", encoding="utf-8") as f:
             json.dump(install, f, default=str)
 
+    _restore_site(cmd, preserved_site)
+
     LOGGER.verbose("Install complete")
 
 

tests/test_install_command.py

@@ -230,3 +230,62 @@ def test_merge_existing_index_not_valid(tmp_path):
     new = [1, 2, 3]
     IC._merge_existing_index(new, existing)
     assert new == [1, 2, 3]
+
+
+def test_preserve_site(tmp_path):
+    root = tmp_path / "root"
+    preserved = tmp_path / "_root"
+    site = root / "site-packages"
+    not_site = root / "site-not-packages"
+    A = site / "A"
+    B = site / "B.txt"
+    C = site / "C.txt"
+    A.mkdir(parents=True, exist_ok=True)
+    B.write_bytes(b"")
+    C.write_bytes(b"original")
+
+    class Cmd:
+        preserve_site_on_upgrade = False
+        force = False
+        repair = False
+
+    state = IC._preserve_site(Cmd, root)
+    assert not state
+    assert not preserved.exists()
+    Cmd.preserve_site_on_upgrade = True
+    Cmd.force = True
+    state = IC._preserve_site(Cmd, root)
+    assert not state
+    assert not preserved.exists()
+    Cmd.force = False
+    Cmd.repair = True
+    state = IC._preserve_site(Cmd, root)
+    assert not state
+    assert not preserved.exists()
+
+    Cmd.repair = False
+    state = IC._preserve_site(Cmd, root)
+    assert state == [(site, preserved / "0"), (None, preserved)]
+    assert preserved.is_dir()
+
+    root.rename(root.parent / "ex_root_1")
+    IC._restore_site(Cmd, state)
+    assert root.is_dir()
+    assert A.is_dir()
+    assert B.is_file()
+    assert C.is_file()
+    assert b"original" == C.read_bytes()
+    assert not preserved.exists()
+
+    state = IC._preserve_site(Cmd, root)
+    assert state == [(site, preserved / "0"), (None, preserved)]
+
+    assert not C.exists()
+    C.parent.mkdir(parents=True, exist_ok=True)
+    C.write_bytes(b"updated")
+    IC._restore_site(Cmd, state)
+    assert A.is_dir()
+    assert B.is_file()
+    assert C.is_file()
+    assert b"updated" == C.read_bytes()
+    assert not preserved.exists()