Prevent crash when macro is in different file

This was caused by a macro in a different file.
The `target.span` was be in the file of the macro definition and the
`item.span` in the file of the calling code.

clippy_lints/src/types.rs

@@ -12,7 +12,7 @@
 use syntax::ast::{FloatTy, IntTy, UintTy};
 use syntax::codemap::Span;
 use syntax::errors::DiagnosticBuilder;
-use utils::{comparisons, higher, in_constant, in_external_macro, in_macro, last_path_segment, match_def_path, match_path,
+use utils::{comparisons, differing_macro_contexts, higher, in_constant, in_external_macro, in_macro, last_path_segment, match_def_path, match_path,
             match_type, multispan_sugg, opt_def_id, same_tys, snippet, snippet_opt, span_help_and_lint, span_lint,
             span_lint_and_sugg, span_lint_and_then, clip, unsext, sext, int_bits};
 use utils::paths;
@@ -1714,6 +1714,10 @@ fn suggestion<'a, 'tcx>(
                 vis.visit_ty(ty);
 
                 for target in &vis.found {
+                    if differing_macro_contexts(item.span, target.span()) {
+                        return;
+                    }
+
                     let generics_suggestion_span = generics.span.substitute_dummy({
                         let pos = snippet_opt(cx, item.span.until(target.span()))
                             .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)))

tests/auxiliary/test_macro.rs

@@ -0,0 +1,11 @@
+pub trait A {}
+
+macro_rules! __implicit_hasher_test_macro {
+    (impl< $($impl_arg:tt),* > for $kind:ty where $($bounds:tt)*) => {
+        __implicit_hasher_test_macro!( ($($impl_arg),*) ($kind) ($($bounds)*) );
+    };
+
+    (($($impl_arg:tt)*) ($($kind_arg:tt)*) ($($bounds:tt)*)) => {
+        impl< $($impl_arg)* > test_macro::A for $($kind_arg)* where $($bounds)* { }
+    };
+}

tests/ui/implicit_hasher.rs

@@ -83,4 +83,11 @@ pub fn $name(_map: &mut HashMap<i32, i32>, _set: &mut HashSet<i32>) {
 gen!(impl);
 gen!(fn bar);
 
+// When the macro is in a different file, the suggestion spans can't be combined properly
+// and should not cause an ICE
+// See #2707
+#[macro_use]
+#[path = "../auxiliary/test_macro.rs"] pub mod test_macro;
+__implicit_hasher_test_macro!(impl<K, V> for HashMap<K, V> where V: test_macro::A);
+
 fn main() {}