Remove warning of duplicated error code

[GuillaumeGomez]

r? @Manishearth

[bstrie]

@GuillaumeGomez can you be more specific about what this does, for posterity? Is there an open issue for the correction here?

[GuillaumeGomez]

It just removes the warning that the E0015 error code appears more than one in the code:

diagnostic code E0015 already used

[ebfull]

I think the function (and the use of Session) should be closer in scope to the actual place it's used, since it's very specific for this situation and shouldn't be used elsewhere. Once const functions stabilize we can refactor it out.

On that note, it might be interesting to add a :reuse flag of some kind to the span_err! macro for this situation in the future, though it might not buy us much.

[Manishearth]

The more idiomatic thing to do here is to use a single span_err call, and use an if to decide what string to pass it (let foo = if ...{format!(...)} else {format!(...)}; span_err(code, str))

[GuillaumeGomez]

You're hard on business haha ! I moved the function to a more little scope as suggested.

[arielb1]

@GuillaumeGomez

Squash and use better names for the parameters (e.g. pass tcx instead of sess). r+ modulo that.

[GuillaumeGomez]

@arielb1: Done !

[Manishearth]

@bors r+ rollup

[bors]

📌 Commit 22f7e96 has been approved by Manishearth

[arielb1]

@bors r-

Sorry, tcx: &Session just doesn't cut it (pass v.tcx - it has the type &ty::ctxt).

[GuillaumeGomez]

Updated !

[arielb1]

@bors r+ rollup

[bors]

📌 Commit 08181d2 has been approved by arielb1