Tags macro does not respect excludeLists

[FND]

The Tags macro does not respect the excludeLists tag; tags tagged with excludeLists still show up in the list.

[FND]

related: #515

[FND]

Fixed in changeset:9465.

[FND]

This fix was accidentally reverted in changeset:9493.

[MartinBudden]

Fixed in changeset:10053

[EricShulman]

The current fix DOES work... however, because it invokes store.getTiddler() within the 'for each tag' loop, it changes the performance profile from O(n) to O(n²), which might add a notable amount of overhead, especially in documents with many tiddlers that have extensive tagging.

Here's the current code (as of TW253):

	for(var t=0; t<tiddler.tags.length; t++) {
		var tag = store.getTiddler(tiddler.tags[t]); 
		if(!tag || !tag.tags.contains("excludeLists")) { 
			...
		}
	}

a more efficient approach would involve peforming a single linear lookup to retrieve the list of all excludeLists-tagged titles *before* the loop and then, within the loop simply check to see if a given tag is in that pre-fetched list, like this:

	var excluded=[];
	store.forEachTiddler(function(title,tiddler) {
		if (tiddler.isTagged("excludeLists") excluded.push(title);
	});
	for(var t=0; t<tiddler.tags.length; t++) {
		if (!excluded.contains(tiddler.tags[t]) {
			...
		}
	}

[MartinBudden]

Tiddlers are stored in a hashmap, so store.getTiddler() is O(1), not O(n), so the performance of the loop is still O(n).

[EricShulman]

The O(1) load for getTiddler() is true for an unmodified TW core. However, plugins (e.g. IncludePlugin?) can hijack getTiddler() in order to provided access to extended 'multi-store' tiddler data, so the overhead for getTiddler() *might* be O(n) or worse, depending upon exactly what plugins are installed, resulting in O(n²) for the whole tags macro loop. The suggested change should result in O(n), regardless of any plugin-enhanced extensions to the core.

Still, this might not produce that much of a performance improvement... but it's worth considering...

[MartinBudden]

Performance not an issue in the core case. Hijackers of getTiddler need to be aware of any performance issues they may introduce in this and other areas.