Fix "Save settings" crash on disabled port; show plugin version in tab

[nothing-stops-this-train]

1. Fix: "Save settings" crashes when the HTTP port is disabled

Saving settings with the HTTP port set to 0 ("disabled") crashed with:

File ".../swapserver_gui/qt.py", line 223, in on_save
    self.config.SWAPSERVER_PORT = new_port
...
File ".../electrum/simple_config.py", line 316, in delete_key
    d.pop(key, None)
AttributeError: 'NoneType' object has no attribute 'pop'

Root cause

on_save turned a spinbox value of 0 into None. SWAPSERVER_PORT is registered by Electrum's bundled swapserver plugin as the dotted key plugins.swapserver.port, so assigning None routes into SimpleConfig's key-deletion branch, whose recursion walks the dotted path without checking that each intermediate dict exists:

# electrum/simple_config.py
prefix, suffix = key.split('.', 1)
d2 = d.get(prefix)          # None when 'plugins.swapserver' was never written
empty = delete_key(d2, suffix)

This plugin only ever writes plugins.swapserver_gui.*, so unless the user has separately enabled and configured the bundled swapserver plugin, plugins.swapserver does not exist and the delete always raises. Reproduced against a real SimpleConfig:

user_config state	result
{} (fresh config)	AttributeError: ... has no attribute 'get'
{'plugins': {'swapserver_gui': {...}}}	... has no attribute 'pop' ← the reported traceback
{'plugins': {'swapserver': {'port': 5455}}}	OK
{'plugins': {'swapserver': {}}}	OK

Because the port write came first, its crash also silently discarded the fee, PoW-target and relay writes — nothing was saved at all.

Fix

A disabled port is now stored as 0, never None. Every reader tests the key for truthiness (electrum/submarine_swaps.py, electrum/plugins/swapserver/server.py, and this plugin's can_run / start_server / status), so 0 is behaviourally identical but takes the ordinary write path. Configs already holding None still load correctly.

This is an upstream Electrum bug; the workaround belongs here because users run released AppImages we cannot patch.

Two supporting changes:

• The writes moved into a GUI-agnostic swapserver_gui.save_settings(). PyQt6 is unavailable in CI, so anything reachable only through qt.py is effectively untestable — which is exactly why the existing suite (built on an attribute-bag config fake) never caught this.
• on_save now catches save failures, logs them, and reports them via show_error instead of letting them escape into the Qt event loop as an unhandled-exception traceback.

2. Feature: plugin version in the tab header

The tab header now shows the installed version, dimmed, between the status text and the enable/disable button:

┌──────────────────────────────────────────────┐
│ Swap server: running    v0.2.1  [ Disable ]  │
├──────────────────────────────────────────────┤

The git tag is the single source of truth. _version.py is committed with the placeholder dev; contrib/make_zip.sh stamps the real value into a staging copy while building the archive, so the working tree is never modified. CI stamps ${GITHUB_REF_NAME#v} on v* tags and dev-g<sha7> otherwise, then verifies the stamp actually landed in the zip.

So a release asset can never disagree with the tag it was built from, a branch/PR zip is always traceable to its commit, and cutting a release needs no in-tree bump — just push the tag. Release builds render v0.2.1; dev stamps render verbatim (vdev would read as a release).

Tests

83 pass (python3 -m unittest discover -s tests). New coverage:

• tests/test_settings_save.py — drives a real SimpleConfig (not the fake) across all four user_config shapes above; asserts later writes survive a disabled port, values persist across a simulated restart, and plugins.swapserver_gui.enabled is not collaterally pruned by upstream's empty-parent-dict cleanup (that would uninstall the plugin on save). Plus a static AST guard against direct SWAPSERVER_PORT assignment in qt.py — verified to fire on the pre-fix code at line 223, the exact line from the traceback.
• tests/test_version.py — version formatting, and the stamping contract make_zip.sh depends on (drift there would silently ship dev in a release).
• tests/test_zip_plugin_load.py — end-to-end: a stamped version reaches the running module when the zip is loaded the way Electrum loads it; unstamped builds keep the placeholder; the working tree stays clean; malformed version strings fail the build rather than emitting a broken _version.py.

Not covered

The QLabel rendering and the show_error dialog itself cannot be exercised — PyQt6 is not installable in this environment or in CI. The logic behind both (version formatting, the persist function and its failure mode) is covered; only the widget wiring is not.

🤖 Generated with Claude Code

https://claude.ai/code/session_013zETFC6MhnsCuxvQDGxqV5