Spelling suggestions should consider trailing exclamation points

[bstrie]

< sawrubh> suppose I wrote assert instead of assert!, I get this message
           : unresolved name: `assert`. Did you mean: `result`? what's
           the thing which generates the last suggestion
< sawrubh> I think that suggesting that I'm missing an ! would be more
           helpful, so just wondering who decides and how it decides what
           to suggest as the solution

As an aside, assert -> result is still a hilariously large edit distance.

[sawrubh]

The search should be first if the spelling mistake is a part of the macros or some other keyword in the language and try and match it with that. If that fails only then suggest other local variables as the correction.

[thestinger]

@sawrubh: I think edit distance takes care of this fine. I don't think ert should autocorrect to assert! instead of a local variable called cert. Heuristics like that would just hurt.

[emberian]

I think it should suggest a macro if the identifier is identical, but it shouldn't suggest it otherwise

[huonw]

Still an issue:

fn main() {
    let result = 1i;
    assert(true);
}

<anon>:3:5: 3:11 error: unresolved name `assert`. Did you mean `result`?
<anon>:3     assert(true);
             ^~~~~~

[frewsxcv]

Still an issue (same input/output as @huonw's comment above)

[Manishearth]

This can be done by holding on to the SyntaxEnv (or just a vec of strings built from the syntaxenv) after expand_crate and passing it down to librustc_resolve through the driver. Not exactly a clean solution, but not too bad either.

[Manishearth]

Opened #29968