Add clear method to EntityDocument

[jakobw]

By letting entities clear themselves we can get rid of type-specific clearing logic in EditEntity, i.e.

• getting rid of Property specific logic in EditEntity from re-adding the data type
• not resetting the FormId counter for Lexemes

Related patch: https://gerrit.wikimedia.org/r/#/c/429792/

Task on Phabricator: https://phabricator.wikimedia.org/T192264

[JeroenDeDauw]

This mistake keeps haunting me :) I've been thinking this is an anti-pattern for years, but people are still copying my shitty code :)

I suggest to create dedicated tests:

testClearClearsSitelinks() {
$item = newItem();
$item->clear();
$this->suchAssert();
}
testClearClearsStatements() {
$item = newItem();
$item->clear();
$this->suchAssert();
}
testClearDoesNotClearId() {
$item = newItem();
$item->clear();
$this->suchAssert();
}

[JeroenDeDauw]

Some clarification happened on IRC and I do not object to leaving the code as is, though think I'd be cool to ditch the instanceProvider call

[JeroenDeDauw]

How is this interface intended to be used? Will there be instanceof checks? Somehow it seems strange to me.

If this is only meant for Entities, calling it ClearableEntity is more obvious (even if it is in the Entity NS).

[jakobw]

ClearableEntity does make it clearer (pun intended). Renamed.
Regarding its use: See the two bullet points and the gerrit patch I mention in the description here. Ideally we're getting rid of instanceof checks. A different question would be whether this should just be part of EntityDocument? Up for debate.

[JeroenDeDauw]

Funny method. Got depracted, undeprecated, deprecated again, removed, and now added again.

Removal happened in 6.0: #614

No objection from my side to re-adding it, especially if there is no way to construct a new empty entity of the same type.

[JeroenDeDauw]

Two points to consider:

• Assigning new objects to the fields rather than calling clear on them breaks references. No idea if this is good or bad for this code
• Maybe a version without mutation (more functional) is possible. Something like $entity->newWithSameId() or $entity->newWithId( $entity->getId() )