Improve error message when type is unknown

[bstrie]

fn main() {
    1.bar();
}

Compiling this gives:

error: attempted access of field `bar` on type `<VI0>`, but no field or method with that name was found.

I'm guessing that the compiler hasn't inferred a type for <VI0>, but it should probably be more explicit about this fact rather than spitting out something that looks like a compiler error. Nothing fancy, it could just look like:

error: attempted access of field `bar` on type `<unknown integral type>`, but no field or method with that name was found.

(Here I'm presuming that a type like <VI0> is known to be integral, where this error occurs more generally it might say <V0>, which should simply become <unknown type>.)

If this can happen in other error messages it should be improved there as well.

---

Here's a test case with another error message that would likely be improved by the fixing this bug:

trait T {
    fn foo();
}

fn bar<V: T>(v: @V) {
    v.foo();
}

fn main() {
    bar(5);
}

Current output:

5124.rs:10:8: 10:9 error: mismatched types: expected `@<V0>` but found `<VI0>` (expected @-ptr but found integral variable)
5124.rs:10     bar(5);
                   ^

Suggested fixed output:

5124.rs:10:8: 10:9 error: mismatched types: expected `@<unknown type>` but found `<unknown integral type>` (expected @-ptr but found integral variable)
5124.rs:10     bar(5);
                   ^

[pnkfelix]

Not critical for 0.6; de-milestoning

[catamorphism]

Nominating for milestone 5, production-ready

[pnkfelix]

accepted for production ready

[bstrie]

Updated with the test case for #5124.

[pcwalton]

Triage bump

[mo]

Another example is this snippet:

fn main() {
    let i = 1;
    if (i % 3 || i % 5)
    {
        println("hello");
    }
}

repro.rs:3:8: 3:22 error: binary operation || cannot be applied to type <VI0>

Ideal error imo would be:
repro.rs:3:8: 3:22 error: binary operation || cannot be applied to integral types

[pnkfelix]

we believe this is fixed, or at least the message quality has been improved.

[pnkfelix]

closing as believed to be fixed.

[alexcrichton]

This appears fixed by #11513