"snippet" for "did you mean `x`" is not so helpful

[nikomatsakis]

On current beta, at least, I see:

error: attempted access of field `test_results` on type `TestResult`, but no field with that name was
 found
   --> src/main.rs:196:25
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^
    |
help: did you mean `results`?
   --> src/main.rs:196:37
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                                     ^^^^^^^^^^^^

But I feel like I'd rather see:

error: attempted access of field `test_results` on type `TestResult`, but no field with that name was
 found
   --> src/main.rs:196:25
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                                     ^^^^^^^^^^^^
    =  help: did you mean `results`?

Come to think of it, we could shorten the main message and move the suggestion into the label, as I think you've done elsewhere:

error: no field `test_results` on type `TestResult`
   --> src/main.rs:196:25
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                                     ^^^^^^^^^^^^ did you mean `results`?
    |

Standalone example:

https://is.gd/8STXMd

cc @jonathandturner

[durka]

Another possibility is to actually replace it

error: attempted access of field `test_results` on type `TestResult`, but no field with that name was
 found
   --> src/main.rs:196:25
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^
    |
help: did you mean `results`?
   --> src/main.rs:196:37
    |
196 |         tests_passed += normal_test.results.iter().filter(|t| t.status == "ok").count();
    |                                     ^^^^^^^

But if it's only a guess, that might not be a good idea.

[nikomatsakis]

@durka my inclination is that the extra 5 lines of output aren't valuable enough in this case, it's not likely it's tricky to figure out how to apply the change

[sophiajt]

Or maybe even...

error: attempted access of field `test_results` on type `TestResult`, but no field with that name was
 found
   --> src/main.rs:196:25
    |
196 |         tests_passed += normal_test.test_results.iter().filter(|t| t.status == "ok").count();
    |                                     ^^^^^^^^^^^^ did you mean `results`?

[nikomatsakis]

@jonathandturner how is that different from my 3rd example? (Except for using a longer "error' message)

[sophiajt]

@nikomatsakis - lol are you sure you didn't add it after I commented?

Just kidding, I just didn't see it the first time through.

[sophiajt]

My vote is your # 3 ;)

[nikomatsakis]

I'm happy to mentor the change. It seems like it would be fairly self-contained. The error is reported by this code in src/librustc_typeck/check/mod.rs -- just search for "attempted access of field" and you ought to find it.

The idea would be to

• change the main message there to something shorter, like "no field {} in type {}"
• change the expr.span in self.type_error_struct(expr.span to field.span, so that we highlight just the field name itself
• change the suggest_field_names function so that instead of calling err.span_help it calls err.span_label

I think that will basically do it!

[nikomatsakis]

One wrinkle I am not sure about: the changes that I suggested above will, iirc, cause a ^^^ with no suggestion to appear in the case that we don't have a suggested field name to offer. I feel like we wanted to move away from those, which might suggest that we ought to offer a generic label like "this field here" or something? <-- @jonathandturner ?

[sophiajt]

Yes, a default label would be great when we don't know the name. Maybe something like "^^^^ unknown field" when we don't know of a good suggestion

[aravind-pg]

I'd love to try my hand at this. The instructions posted seem sufficient for now, but I'll come back if I have any questions.