Type errors of the form "expected... but found..." should indicate the source of their expectation

[zwarich]

The program

extern crate collections;
use collections::treemap::TreeMap;

fn main() {
    let mut a = TreeMap::new();
    a.insert(0, 1);
    a.insert(0, "foo");
}

gives the type error

treemap-test.rs:7:17: 7:22 error: mismatched types: expected `<generic integer #1>` but found `&'static str` (expected integral variable but found &-ptr)
treemap-test.rs:7     a.insert(0, "foo");
                                   ^~~~~

This error should indicate the source of the expectation that the type parameter is integral.

[steveklabnik]

Updated code:

use std::collections::BTreeMap;

fn main() {
    let mut a = BTreeMap::new();
    a.insert(0, 1);
    a.insert(0, "foo");
}

Error

 expected `_`,
    found `&'static str`
(expected integral variable,
    found &-ptr) [E0308]
hello.rs:6     a.insert(0, "foo");
                           ^~~~~

It still does not point to insert(0, 1).

[Havvy]

Triage: No change.