transactional facilities are not implemented for ty_ivar

[nikomatsakis]

The infer module has transactional capabilities for rolling back changes to type/region variables, but these are not being used for integral type variables. We have to modify the methods commit(), try(), and probe() to do something comparable to what is being done for the tvb variable.

Here is a test that displays undesirable behavior as a result:

impl methods for uint {
    fn foo() -> ~str { ~"uint" }
}
impl methods for int {
    fn foo() -> ~str { ~"int" }
}
fn main() {
    assert 22.foo() == ~"int";
}

Actually a naive fix for this will probably lead to an ambig method call error. I am not sure if this is the right thing or not.

[pnkfelix]

Porting Niko's original example to more modern syntax:

trait methods         { fn foo(&self) -> ~str;            }
impl methods for uint { fn foo(&self) -> ~str { ~"uint" } }
impl methods for int  { fn foo(&self) -> ~str { ~"int"  } }

fn main() {
    assert!(22.foo() == ~"int");
}

I indeed get an error due to multiple applicable methods:

% rustc /tmp/bug5.rs
/tmp/bug5.rs:6:12: 6:23 error: multiple applicable methods in scope
/tmp/bug5.rs:6     assert!(22.foo() == ~"int");
                           ^~~~~~~~~~~
<core-macros>:52:4: 69:5 note: in expansion of assert!
/tmp/bug5.rs:6:4: 6:32 note: expansion site
/tmp/bug5.rs:2:24: 2:57 note: candidate #1 is `__extensions__::foo`
/tmp/bug5.rs:2 impl methods for uint { fn foo(&self) -> ~str { ~"uint" } }
                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/bug5.rs:3:24: 3:57 note: candidate #2 is `__extensions__::foo`
/tmp/bug5.rs:3 impl methods for int  { fn foo(&self) -> ~str { ~"int"  } }
                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

which seems like the right thing to me in this context. Niko, feel free to re-open if I have misunderstood the crux of the bug.