error[E0463]: can't find crate for `non_existent`
  --> $DIR/multiple-extern-by-macro-for-inexist.rs:5:1
   |
LL | extern crate non_existent;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

error[E0259]: the name `non_existent` is defined multiple times
  --> $DIR/multiple-extern-by-macro-for-inexist.rs:10:9
   |
LL | extern crate non_existent;
   | -------------------------- previous import of the extern crate `non_existent` here
...
LL |         extern crate std as non_existent;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `non_existent` reimported here
...
LL | m!();
   | ---- in this macro invocation
   |
   = note: `non_existent` must be defined only once in the type namespace of this module
   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you can use `as` to change the binding name of the import
   |
LL |         extern crate std as other_non_existent;
   |

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0259, E0463.
For more information about an error, try `rustc --explain E0259`.