Rollup merge of #54488 - zackmdavis:and_the_case_of_the_unused_crate, r=estebank

in which we include attributes in unused `extern crate` suggestion spans

![unused_extern](https://user-images.githubusercontent.com/1076988/45921698-50243e80-be6f-11e8-930a-7b2a33b4935c.png)

Resolves #54400.

r? @estebank

diff --combined src/librustc_typeck/check_unused.rs
index de4ab527e1559c155702bf5057bf312b8fa8b78d,3dbd5f2017ee492a85dbdae888bd4d24e76f4418..62ffffab07661304f48df4af1bdd9a0baa587413
--- 1/src/librustc_typeck/check_unused.rs
--- 2/src/librustc_typeck/check_unused.rs
+++ b/src/librustc_typeck/check_unused.rs
@@@ -75,7 -75,7 +75,7 @@@ impl<'a, 'tcx> CheckVisitor<'a, 'tcx> 
          let msg = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
              format!("unused import: `{}`", snippet)
          } else {
 -            "unused import".to_string()
 +            "unused import".to_owned()
          };
          self.tcx.lint_node(lint::builtin::UNUSED_IMPORTS, id, span, &msg);
      }
@@@ -130,17 -130,25 +130,23 @@@ fn unused_crates_lint<'tcx>(tcx: TyCtxt
      });
  
      for extern_crate in &crates_to_lint {
 -        assert!(extern_crate.def_id.is_local());
 +        let id = tcx.hir.as_local_node_id(extern_crate.def_id).unwrap();
 +        let item = tcx.hir.expect_item(id);
  
          // If the crate is fully unused, we suggest removing it altogether.
          // We do this in any edition.
          if extern_crate.warn_if_unused {
              if let Some(&span) = unused_extern_crates.get(&extern_crate.def_id) {
 -                assert_eq!(extern_crate.def_id.krate, LOCAL_CRATE);
 -                let hir_id = tcx.hir.definitions().def_index_to_hir_id(extern_crate.def_id.index);
 -                let id = tcx.hir.hir_to_node_id(hir_id);
                  let msg = "unused extern crate";
+ 
+                 // Removal suggestion span needs to include attributes (Issue #54400)
+                 let span_with_attrs = tcx.get_attrs(extern_crate.def_id).iter()
+                     .map(|attr| attr.span)
+                     .fold(span, |acc, attr_span| acc.to(attr_span));
+ 
                  tcx.struct_span_lint_node(lint, id, span, msg)
                      .span_suggestion_short_with_applicability(
-                         span,
+                         span_with_attrs,
                          "remove it",
                          String::new(),
                          Applicability::MachineApplicable)
@@@ -155,13 -163,6 +161,13 @@@
              continue;
          }
  
 +        // If the extern crate isn't in the extern prelude,
 +        // there is no way it can be written as an `use`.
 +        let orig_name = extern_crate.orig_name.unwrap_or(item.name);
 +        if !tcx.sess.extern_prelude.contains(&orig_name) {
 +            continue;
 +        }
 +
          // If the extern crate has any attributes, they may have funky
          // semantics we can't faithfully represent using `use` (most
          // notably `#[macro_use]`). Ignore it.
@@@ -170,6 -171,9 +176,6 @@@
          }
  
          // Otherwise, we can convert it into a `use` of some kind.
 -        let hir_id = tcx.hir.definitions().def_index_to_hir_id(extern_crate.def_id.index);
 -        let id = tcx.hir.hir_to_node_id(hir_id);
 -        let item = tcx.hir.expect_item(id);
          let msg = "`extern crate` is not idiomatic in the new edition";
          let help = format!(
              "convert it to a `{}`",