Fix "No module named 'swapserver_gui'" crash when installing the zip

[nothing-stops-this-train]

Installing the v.0.13 plugin zip in Electrum crashes with:

ModuleNotFoundError: No module named 'swapserver_gui'

Cause

qt.py and swapserver_gui.py both used from . import pow as swap_pow. That import form is unsafe for an Electrum external zip plugin.

electrum/plugin.py: maybe_load_plugin_init_method registers the package in sys.modules as electrum_external_plugins.swapserver_gui, but builds its spec with zipimport.zipimporter(zip).find_spec('swapserver_gui') — so the package object's __name__ stays the bare swapserver_gui:

sys.modules key   : electrum_external_plugins.swapserver_gui
module.__name__   : swapserver_gui          <-- what _handle_fromlist uses
'swapserver_gui' in sys.modules: False

CPython's importlib._bootstrap._handle_fromlist builds the submodule name as '{}.{}'.format(module.__name__, x), so from . import pow resolved to swapserver_gui.pow, whose parent is not importable.

Only v.0.13 is affected — pow.py and these imports arrived with the shutdown-hang fix. from .swapserver_gui import ... was never affected: a non-package module has no __path__, so _handle_fromlist skips that branch and resolution goes through __package__.

Fix

swap_pow = importlib.import_module('.pow', __package__). __package__ comes from the submodule's own correctly-dotted spec, so it works for both the zip and the directory layout. All 9 swap_pow. call sites and the 'swap_pow.PowState' annotations are unchanged.

Tests

The existing suite could not catch this: it puts plugins/ on sys.path and imports the package as a top-level swapserver_gui, where __name__ does match the sys.modules key.

tests/test_zip_plugin_load.py adds:

• an AST guard rejecting from . import <submodule> in the plugin sources — covers qt.py without needing PyQt6 — plus a check that the guard actually fires;
• an end-to-end test that builds the real zip via contrib/make_zip.sh and replicates Electrum's loader in a subprocess with plugins/ deliberately off sys.path, asserting the bare name is genuinely unimportable so the test is not vacuous (a fresh interpreter is required anyway, since ConfigVar asserts each key registers exactly once);
• a test that the directory layout still imports as a top-level package.

Reverting the two import lines fails the new tests. With the fix: 59 tests, OK.

🤖 Generated with Claude Code

https://claude.ai/code/session_013zETFC6MhnsCuxvQDGxqV5