Better error message when users mistakenly import from named vs. default export

[alexeagle]

At google, we've had a number of users trip over import syntax when working with libraries that have default exports.

Given this scenario:

has_named_export.ts

export var a = 1;

has_default_export.ts

var b = '';
export default b;

1. Users often do:

import {b} from './has_default_export';

which gives:
Error: module has no exported member 'b'

Request: the error could be more helpful, like "did you mean to import the default export, with no curly braces"
This is especially likely when the name of the default export matches the named import.
Novice users look at has_default_export and think that B should be importable, and may never have worked with default exports.

2. Also possible:

import a from './has_named_export';

"has_named_export" has no default export

This one is less frequent, but it could say "did you mean to import the named import 'a' by using curly braces"

[mhegazy]

Should be a rather simple check in getExternalModuleMember to add the elaboration. PRs are welcomed.

[jules-costa]

I'd like to give this a shot! This would be my first open source contribution.

[RyanCavanaugh]

@jules-costa the closed PRs referenced above are fairly close to correct - I'd recommend picking out the good bits from those changes

[knrt10]

@jules-costa are you still working on this issue? If not, I would like to give it a try.

[joaniedavis]

@knrt10 Are you still working on this issue? If not, could I take over your PR and update it with the requested fixes?

[knrt10]

@joaniedavis I was little busy, but sure go ahead.