Use spans for -Z external-macro-backtrace

[estebank]

% rustc ui/type-check/cannot_infer_local_or_vec.rs -Z external-macro-backtrace
error[E0282]: type annotations needed
  --> <vec macros>:3:1
   |
1  | / ( $ elem : expr ; $ n : expr ) => (
2  | | $ crate :: vec :: from_elem ( $ elem , $ n ) ) ; ( $ ( $ x : expr ) , * ) => (
3  | | < [ _ ] > :: into_vec ( box [ $ ( $ x ) , * ] ) ) ; ( $ ( $ x : expr , ) * )
   | | ^^^^^^^^^^^^^^^^^^^^^
   | | |
   | | cannot infer type for `T`
4  | | => ( vec ! [ $ ( $ x ) , * ] )
   | |______________________________- in this expansion of `vec!`
   |
  ::: ui/type-check/cannot_infer_local_or_vec.rs
   |
12 |       let x = vec![];
   |           -   ------ in this macro invocation
   |           |
   |           consider giving `x` a type

error: aborting due to previous error

[rust-highfive]

r? @pnkfelix

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[estebank]

Follow up to #45545 (comment).

CC @durka.

[durka]

Looks really good!

…

On Dec 9, 2017 1:31 PM, "Esteban Kuber" ***@***.***> wrote: Follow up to #45545 (comment) <#45545 (comment)>. CC @durka <https://github.com/durka>. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#46605 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAC3nyYaxTxTqf_JwFCV6b4fJoDN_egQks5s-tIbgaJpZM4Q8MZg> .

[pnkfelix]

... would it be better to move these annotations outside of the macro_rules! pong { ... }? I was a little confused at first by the main.stderr until I realized that they were just transcribed from the source because they happen to occur within the macro definition?

[pnkfelix]

I'm thinking something along the lines of:

// a local macro
macro_rules! pong {
    () => { syntax error };
}
//~^^ ERROR expected one of
//~| ERROR expected one of
//~| ERROR expected one of

but maybe I misremember the exact syntax here.

Its possible that even this may work:

// a local macro
macro_rules! pong {
    () => { syntax error };
} //~^ ERROR expected one of
  //~| ERROR expected one of
  //~| ERROR expected one of

[pnkfelix]

r=me once the //~ERROR annotations are moved outside of the macro. (Or if that turns out not to be possible for some reason, then just r=me. 😄)

[estebank]

@bors r=pnkfelix

[bors]

📌 Commit d4b8e99 has been approved by pnkfelix

[bors]

⌛ Testing commit d4b8e99 with merge 8954b16...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: pnkfelix
Pushing 8954b16 to master...