Suggest which trait to import if method lookup fails

[catamorphism]

This may be a dup, but http://pastebin.com/KkCdjmRS suggests that this error message could be improved:

arguments.rs:17:8: 17:14 error: attempted access of field each on type ['a], but no public field or method with that name was found
arguments.rs:17     for v.each {|elt| acc += [f(elt)]; }

This error message could be better, because it doesn't tell the user what they need to do to fix the problem. In this case, the hint "import the module that defines the implementation that defines each" would be helpful. Obviously there is no hint that would always apply, but this would be helpful in many cases.

[catamorphism]

I think this is only an issue in an older version of rustc, but this could probably still happen when using an impl that's not in the standard library, and it would be good to handle that?

[nikomatsakis]

Part of the problem here is that the code which issues that error has no idea that this is a method call. This could be fixed in various ways... certainly that would be a good flag that indicates an import might be necessary.

[pcwalton]

Edited title.

[alexcrichton]

I'm not sure that the case above is the best test case for this any more. The language seems to have change a lot since then. The major changes is that [T] is no longer a valid vector form, along with values being move-by-default. Technically += isn't defined on a vector any more, and it wouldn't work anyway because there's no U: Copy.

So with that, is there another small case which exhibits this behavior?

[metajack]

Here's an updated test case (I think):

fn main() {
    let s = ~"hello, world";
    do s.foo |cs| {
        // nothing
    }
}

which produces

$ rustc 2508.rs 
2508.rs:3:4: 5:5 error: type `~str` does not implement any method in scope named `foo`
2508.rs:3     do s.foo {
2508.rs:4         // nothing
2508.rs:5     }

I tried several variation of this, but couldn't ever get the unknown field error. I think this is fixed.

[metajack]

Actually, this one trigger it:

fn main() {
    let s = ~"hello, world";
    for _ in s.foo {
        // nothing
    }
}

with

$ rustc 2508.rs 
2508.rs:3:13: 3:18 error: attempted access of field `foo` on type `~str`, but no field with that name was found
2508.rs:3     for _ in s.foo {
                       ^~~~~

It seems like also mentioning this might be trying to resolve a method. Perhaps:

"Type ~str does not have a public field foo or implement any method in scope named foo"

[Kimundi]

@metajack The new for doesn't allow to leave off the (), so that syntax could only look for a field.

[metajack]

Closing then.