Implement regular expression search for tag and tags

[claremacrae]

In Tasks 1.12.0, it will become possible to do regular expression searches on path, heading and description fields.

It would be good to add this to tag/tags searches too.

This sill involve editing src/Query/Filter/TagsField.ts. Ideally, this would be implemented in terms of TextField, to not duplicate any of the code in TextField.

[claremacrae]

When this is implemented, show how to write the following as a regex:

(tags include #context/loc1) OR (tags include #context/loc2) OR (tags include #context/loc3)

Something like:

tags regex matches /#context/loc1|#context/loc2|#context/loc3/

[claremacrae]

This should start by a separate refactoring PR to make TagsField.createFilterOrErrorMessage more consistent with TextField.

For example:

• TextField uses stringIncludesCaseInsensitive() which is locale-aware, whereas as TagsField uses its own tag.toLowerCase().includes(search.toLowerCase()
• Negation in the current code can be simplified like TextField uses its method maybeNegate().

[claremacrae]

This should start by a separate refactoring PR to make TagsField.createFilterOrErrorMessage more consistent with TextField.

For example:

• TextField uses stringIncludesCaseInsensitive() which is locale-aware, whereas as TagsField uses its own tag.toLowerCase().includes(search.toLowerCase()
• Negation in the current code can be simplified like TextField uses its method maybeNegate().

See #1056 for the above changes.

[claremacrae]

I've looked at implementing this a couple of times, and each time I got stuck agonising about this:

            // Search is done sans the hash. If it is provided then strip it off.
            const search = tagMatch[3].replace(/^#/, '');

I don't think the regex filters should strip # out of the query, as this would mess up filtering for start-of-tag /^#a$/.

The more I think about it, the more I think that it is unhelpful that these two searches give identical results:

tags include home
tags include #home

I think if the users supplies a # in their query, it should be honoured.

Currently, searching for tags include #home matches

Changing the above code to the following does not cause any tests to fail:

            const search = tagMatch[3];

[claremacrae]

Logged in #1106

[claremacrae]

This has just been released in 1.13.0

https://obsidian-tasks-group.github.io/obsidian-tasks/queries/filters/#tags
https://obsidian-tasks-group.github.io/obsidian-tasks/queries/regular-expressions/#finding-sub-tags