Return an empty enclosures list for items with no link (fixes #340)

[gaoflow]

Fixes #340.

You agreed back in 2023 that this should not crash; since the issue is still open (and was bumped again in 2024) I put together a fix. Happy to defer if you would rather take it from here.

The bug

Accessing enclosures (or license) on a feed or entry that has an id but no link crashes instead of returning an empty list:

import feedparser
d = feedparser.parse(
    '<feed xmlns="http://www.w3.org/2005/Atom"><entry><id>urn:x</id></entry></feed>'
)
d.entries[0].enclosures      # AttributeError: object has no attribute 'enclosures'
d.entries[0]['enclosures']   # KeyError: 'links'

Reproduced on main (6.0.12) for both Atom and RSS. The documented contract is that enclosures is always a list.

Cause

The computed enclosures and license keys in feedparser/util.py iterate over dict.__getitem__(self, "links"). The links key is only created lazily (setdefault("links", [])) when a <link> is actually parsed, so an entry or feed with no link never gets it, and the iteration raises KeyError: 'links' (surfaced as AttributeError on attribute access).

Fix

Seed an empty links list when an entry (_base.py _start_item) or the feed (mixin.py.__init__) is created. enclosures then returns [] and license is simply absent, matching the docs. Bare FeedParserDict() instances are deliberately left untouched, so test_empty (which asserts enclosures/license are absent on an empty dict) still holds.

The util.py one-liner dict.get(self, "links", []) would be simpler, but it breaks test_empty because it cannot distinguish a parsed-but-link-less object from a bare dict. Seeding at parse time preserves that distinction.

Scope note

The issue is about entries, but the identical crash exists at the feed level (feed.license / feed.enclosures on a feed with no link), so I fixed both. If you would prefer to keep this scoped to the entry case in #340, I am happy to drop the mixin.py change and its fixture.

Tests

Added three well-formed fixtures (an Atom entry, an RSS item, and a feed, each with an id/guid but no link) asserting enclosures == []. Without the fix these fail with KeyError: 'links'; with it the full suite is green (4303 passed, 8 skipped).

Disclosure: I prepared this fix with AI assistance under my direction; I reviewed and verified the change and the tests myself.