Introduce the `ObjectAttributeCompletionProvider` module

[karreiro]

Overview

The goal of this PR is fixing https://github.com/Shopify/theme-check/issues/642* and introducing new intelligent code completion capabilities on Theme Check.

I recommend reviewing this PR by following the sections below. I've split it into meaningful commits to approach each module individually and clarify its purpose.

Steps to review

1. Minor adjustments

• c8c7f3c7e5e13d7df67d611a96fc992b3f17b6b - First of all, we slightly adjust a detail in the Markdown documentation
• 911c53a9ae792a0cb748c97e6b63b160d60e2c8 - Then, we introduce the prototype implementation to support built-in types
  • This module still have some TODO elements: https://github.com/Shopify/theme-check/issues/657

2. Setup our new code completion tools

• 52029b5bf134edb612c5028494fb66123d2f829 - Now, we create the variable_lookup_finder/constants module to hold some regexes (they will be used in the future commits)
• 753ce9a30a05064377b7167dadf6dd10048c817 - Then, we introduce the main module of the type inference, the LiquidFixer
  • It receives a Liquid string and tries to turn it in a valid/parsable Liquid string
  • This module is designed to receive unfinished snippets, as while developers are typing, templates will be probably broken
• 6b458821b1e24f6a954e54a1d806a69e44e1209 - After that, we introduce the AssignmentsFinder module
  • This module relies on a Liquid visitor to get all assign occurrences
  • We still have one missing detail to finish in this module here: https://github.com/Shopify/theme-check/issues/655
• e27f9dfaa43f85042acffd21e57531a1c09948b - With those elements in place, we can now change the VariableLookupFinder to use the AssignmentsFinder and the LiquidFixer modules
  • With them, the VariableLookupFinder can follow variables and get their types based on assignments

3. Improve our code completion suggestions

• 13b37515a63f2f5c922f39ded6c7fafb848dd8b - Cool! We have our new mechanism in place; it's time to use it to provide valuable suggestions
  • But, before that, we need to apply some minor changes
  • The CompletionEngine works as an aggregator of all completion providers (each completion provider extends CompletionProvider)
  • With that in mind, we're changing the CompletionProvider main method from completions(content, cursor) to completions(relative_path, line, col)
  • The goal of this change is empowering each provider to suggest completion items based on the file, the line, and the column (instead of content, which was the current token a subset of the file)
  • Good! We're done with that
  • Now, let's update the existing completion providers and introduce documentation on them as well (as we have it for free now) :)

4. The new ObjectAttributeCompletionProvider provider

• da2c38fe51ca3ecfb474a95a74752aa06c115e8 - Ok, in the latest commits, we updated the existing completion providers, it's time to introduce the new 'ObjectAttributeCompletionProvider' provider
  • Our new provider relies in the new VariableLookupFinder implementation to provide intelligent code completion for attributes
  • Now, we're pretty much done

5. TODO

• fc749d3db443166a055e71e605ff7f3585b0d5b8 & a324fb326570b60601b78537b73f6bf2eaa34ca9 - These commits just introduce some references about the pending work we have

Steps to 🎩

• Setup your editor (VS Code, vim, or nvim) with your local Theme Check by following this guide
• Create a new theme with shopify theme init
• Open your new theme to try code completion
• Notice that filters/tags/objects code completion items have documentation now
• Notice that objects support multi-level attribute code completion now:

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* I've been calling the features introduced by this PR as "type inference" in https://github.com/Shopify/theme-check/issues/642 issue. But, I've decided to break that concept into sub-components into this PR to clarify what each phase means.