Improve error messages

[dilijev]

In order to provide the best possible development experience, we should improve error messages to call out as much information as possible (which parameter, which field, actual/expected types, etc.) when something goes wrong.

Sub-issues:

Fixed

• Fix error message for changing [[Writable]] to true from false for non-configurable properties #424 (fixed)
• Error message for not defined identifiers is confusing (uses the term undefined) #2901

Poor / difficult to understand messages

• Fix the message for implicit Symbol.toString to make it more descriptive #434
• Poor error message for unicode escapes in keywords #2872

Nice-to-have improvements

• Follow up issue [1, 2].sort({}) has unhelpful error message #2411 and PR Change error msg for Array.sort (Fix #2411) #2648 (improved by the PR but still needs more work)

[dilijev]

@ljharb I like #2648 for what it is; in order to provide better messages across the board would be a bigger work item, so I've decided to open this issue to track it.

[liminzhu]

@bterlson

[bterlson]

I am working on a comparison sheet with our errors and other runtimes' errors (based on test262 tests). I will post that here, thanks for creating an issue :)

[dilijev]

Meta:

I don't think Bug (not a functionality problem) or Codebase Quality (IMO more about code cleanliness) really works for this kind of issue. I was thinking of adding a label like Dev Experience but even that seems a bit off or perhaps heavy-handed. For now I'll leave it as Codebase Quality. What do you think @bterlson / @liminzhu?

FYI: https://github.com/Microsoft/ChakraCore/wiki/Label-Glossary

[bterlson]

Agree none of the current labels really apply. I like the idea of "Dev Experience" or even just "Experience". The default label set includes "Improvement" which is another option, too.

[dilijev]

We don't currently have an "Improvement" label.

One reason I don't like Dev Experience is that considering we're a dev tool, there might be confusion as to whether "Dev" refers to users/embedders of ChakraCore (who are devs) or to ChakraCore devs.

Arguably the split is Codebase Quality is for issues that affect devs of ChakraCore and Dev Experience relates to the dev experience we ship. Arguably an issue in the dev experience we ship is a kind of Bug...

I'll probably go with Dev Experience if nobody else chimes in.

[dilijev]

@kfarnung we have this catch-all for error message improvements. Maybe we can dupe any other error-message issues to this one and track as a group?