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Add defense for expensive APIs
Performance can be thought in terms of "Offense" – the changes that you make to actively improve performance – and "Defense" – the systems you have in place to prevent performance regression's (this offense/defense idea from [https://medium.com/@ricomariani/dos-and-don-ts-for-performance-teams-7f52c41b5355?source=rss-e6e91dab0708------2 this blog post]).
== Defense: discouraging use of expensive APIs ==
In some cases, we want to discourage folks from using expensive APIs such as <code>runBlocking</code>. As a first draft solution, we propose a multi-step check:
# Compile-time check throughout the codebase: write a code ownered test asserting the number of references to the API.
## ''Question: given the lint rule, should we just count the number of `@Suppress` for this?''
## ''Question: would it help if this was an annotation processor on our lint rule and we look for <code>@Suppress</code>?''
# Run-time check on critical paths: wrap the API and increment a counter each time it is called. For each critical path (e.g. start up, page load), write a code ownered test asserting the number of calls to the API.
## ''Question: is this too "perfect is the enemy of the good?"''
# Add lint rule to discourage use of the API. This overlaps with the compile-time check, however:
## We can't just use the compile-time check because in the best case it'll only run before the git push – it won't appear in the IDE – and the feedback loop will be too long for devs
## We can't just use the lint rule because it can be suppressed and we won't notice
== App start up ==
