Add support for typecasting in mapping generation on cli init

[travs]

This issue has been raised before (https://github.com/graphprotocol/graph-tooling/issues/949, https://github.com/graphprotocol/graph-tooling/issues/1017), but when generating a new subgraph for a contract that has events with address[] inputs, the generated mappings won't compile properly.

This is due to an issue where arrays of derived types (Address[] in this case) are not assignable to arrays of base types (Bytes[] here).

I wasn't sure how to fix this on a lower level as I'm not familiar with AssemblyScript, so I went and implemented a fix where the mapping assignments generated for events on init are conditionally wrapped with changetype<typeB>(...parameter.of.typeA...) if typeA is not able to be implicitly cast to typeB.

This got a bit messy and I had to extend some functions since we also must add imports for the types we are typecasting as (e.g. Bytes), and these must be calculated before we iterate events inside the template string.

I tested this locally and the generated mappings compile, but I'm not too sure about events with tuples, since they were a special case to begin with. A solution that doesn't do typecasting, but improves the base types or better uses AssemblyScript's existing type system is probably superior to my approach.

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: ca886c83392559704425eff5df86689d7862d485

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR