Copy and paste error messages from the typechecker when using suppression statements

❌Bad:

// $FlowFixMe: greeting isn't null
sayHello(greeting);

✅Good:

// $FlowFixMe: Flow thinks `greeting` is null, but it isn't because xyz (https://example.com/link/to/my/stack/trace)
sayHello(greeting);

(Or link to the error in an inline comment during code review.)

Why?

Your code reviewer can't easily run your code to see what the actual error was. Help them by showing them the error that the typechecker (e.g. Flow or TypeScript) produced. Either:

• copy and paste it as an inline comment in Github (or whatever code review tool you use)
• copy and paste it into a public pastebin (e.g. fluffy.cc) (or company internal equivalent) and link to it in-code in the supression statement comment

Using a supression statement, especially for typecheckers, is a code smell. Something has gone wrong if we're resorting to using one, and it usually indicates that something somewhere else needs to be fixed, such as library type definitions, generated client libraries from swagger specs, or perhaps a bug in the typechecker itself.

This implies that if we're turning off the typechecker, it's either:

1. a placeholder until the underlying issue is fixed (in which case, also give this reason in the supression comment)
2. we're simply turning it off for this line because it's complex to resolve

Either way, you should always copy and paste the error message from the typechecker, so your code reviewer can confirm that your error fits the reason given for (1), or help provide a fix in code to resolve (2).