Code Action for pre-filling required fields

[radeksimko]

Follow-up to #719

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Problem Statement

Users can today introduce a new block into their configuration via completion

However the block is not considered complete/valid until it has all required attributes and blocks.

This means that users have to either scrolls over a potentially long list of attributes and blocks to add all required ones and/or consult documentation in a separate window.

#719 pre-fills required fields on completion (using the completion LSP method) which mainly solves the problem for new blocks.

Expected User Experience

Block with existing attributes/blocks

A contextual code action would be available to the user to fill any missing required attributes and blocks, similar to gopls:

Proposal

• provide new quickfix code action associated with the body of a block which has missing required attributes or blocks