feat(eslint-plugin): add new rule no-misused-promises

[princjef]

Adds a new no-misused-promises rule as discussed previously in #508. Fixes #508

Some notes about the implementation:

• Trying to determine the type of the parameter for which an argument is provided was harder than I expected. The only way I could find to make it work was to enumerate the call signatures of the function being called and matching argument and parameter by index. This can potentially be problematic for functions with many overloads or rest params, but the rule is conservative enough that there should be no false positives in such cases.

• I ended up making the conditional check apply to any situation where the truthiness/falsiness check could end up swallowing a promise. I can't think of any valid use cases where the checks that I have placed will trigger, but I did carve out a case so that code like const foo = someCheck || promise; won't be flagged due to short-circuit evaulation.

• There was no entry in RuleListener for LogicalExpression, so I added it to the type and everything seemed to work. I'm assuming this was just an omission from the type.

[codecov]

Codecov Report

Merging #612 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #612      +/-   ##
==========================================
+ Coverage   94.33%   94.43%   +0.09%     
==========================================
  Files         111      112       +1     
  Lines        4593     4672      +79     
  Branches     1268     1286      +18     
==========================================
+ Hits         4333     4412      +79     
  Misses        149      149              
  Partials      111      111

Impacted Files	Coverage Δ
...ges/eslint-plugin/src/rules/no-misused-promises.ts	100% <100%> (ø)
packages/eslint-plugin/src/rules/index.ts	100% <100%> (ø)	⬆️

[JamesHenry]

Great work! Thanks for doing this

Stale

[bradzacher]

awesome! great work - thanks for the contribution.

[twavv]

Related (but a few months late):
I've opened this issue on TypeScript itself to make using a promise in a condition a compiler error (microsoft/TypeScript#34717) à la the change in 3.7 to make non-nullable functions in conditions an error.