Error UX Improvement Sync, 6/28/2018

[DanielRosenwasser]

Stripping null and undefined from targets

#25287

• We already avoid elaborating when relating primitives to unions.
• Action item: don't work on primitives, just work on objects.

User Test Suite

#25294

• Signed off
• @andy-ms, can you take a look at that weird change?

Exposing diagnostic codes to related error spans

#25304

• Should codes be Error? Suggestion? Info?
• Discuss in issue.

Related Error Spans

#25257

• Reprioritized
• Duplicate declaration/redeclared block scoped variable errors
  • Having the link to the declarations is useful
  • But usually it's not that you have 100 of the same error, it's usually that you have 100 errors in two files respectively (because they're identical).
  • Maybe limit 5 duplicate declaration error within a file, taper off with "N other duplicates have been detected"
  • If all the top-level declarations are duplicate, potentially just consider the file a duplicate?
  • Maybe say "File A duplicates identifiers x, y, z, a, ..., q from file B".
    • This one seems good.
    • We'll figure out how to do it
  • Action item: file an issue for better consolidation.

Most searched errors (?)

• We literally typed in error TS into Google and let it auto-complete.
  • Probably good enough.
• TS2339, TS2307, TS2304, TS2322, TS2531, TS1005, TS2305, TS2345, TS2306
• "error ts2304 cannot find name"
  • Google completes with require, map, buffer, describe, $, asyncIterator, process, symbol, module, promise
  • Should we provide a better error on these?
    • Yes!
  • You're using $ => Suggest jQuery
  • You're using describe => Did you mean to have types for mocha, jest, etc.?
  • process, require, module => Node types
  • Symbol, Promise, Map, Set, asyncIterator => Different lib or target.
  • Action item: Better elaborations
• "error ts2531 object is possibly 'null/undefined'"
  • What can we do?
    • Possibly tell people to use the !?
    • Might be the wrong way to lead users down the right path.
• "Typescript error TS1005: ';'"
  • Recurring issue with Visual Studio installations not overriding existing tsc.
• "Argument of type X is not assignable to parameter of type Y"
  • https://stackoverflow.com/questions/34738799/argument-of-type-x-is-not-assignable-to-parameter-of-type-x
  • This is the first result
    • And the top answer is https://stackoverflow.com/a/34738923!
  • Really, you want to know that you meant to call the value.
  • Need to know you're checking in an expression context.
  • Action item: Create better error message for uncalled values
• "File is not a module"
  • How do we explain modules to people in the terminal?
  • Could provide an explanation in every error
    • Becomes noisy
      • Rust has a suggestion to run with --showElaborations.
  • Provide a link?
    • But you don't want to provide a link for every error.
  • "Consider searching Google for-"
    • lol

[RyanCavanaugh]

We could run the numbers on @types packages by download count and make a reverse map from the globals they expose => suggestions for things to install. A quickfix would turn it into an amazing demo...

[mhegazy]

We can do that as part of #25308. we just need a json file of sorts that map global variable to a package file, and the compiler can use that.