Prevent redundant token rate updates

[mcmire]

Explanation

The token rates controller fetches rates for certain collections of tokens obtained via the tokens controller. If any of these collections change, then new rates need to be fetched.

Unfortunately, because the check to determine whether these collections have changed is simplistic, new rates are fetched every single time the tokens controller state is changed.

To address this, we can consider two things:

• The token rates controller only uses the addresses of tokens in these collections to fetch rates, and it also normalizes those addresses when updating state.
• These collections of tokens may contain duplicates.

So to reduce the number of times rates are fetched and to optimize each request, this commit updates the tokens state callback to assemble the aforementioned token collections into a deduplicated, normalized list of token addresses, and then it checks to see if this list has any changes to know whether or not to re-fetch rates.

References

Fixes #3605.

Changelog

@metamask/assets-controllers

• FIXED: Fix TokenRatesController to prevent redundant token rate updates when tokens change
  • Previously, token rates would be re-fetched for the globally selected network on all TokensController state changes, but now token rates are always performed for a deduplicated and normalized set of addresses, and changes to this set determine whether rates should be re-fetched.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate

[mcmire]

By the time we get here, tokenContractAddress is already normalized (thanks to #getTokenAddresses).

[mikesposito]

Looks good!

[cryptodev-2s]

LGTM!

[Gudahtt]

is the toHex call redundant alongside toChecksumHexAddress?

[mcmire]

It's not — unfortunately toChecksumHexAddress (located in controller-utils) doesn't use a type predicate to assert that its return value is a Hex. toHex (which is from @metamask/utils) does, though. So it's redundant in the sense that it doesn't do anything, but it does convert this to a Hex.