Add note to fix MATCH_TYPE_ON_DIAG_ITEM

Author: Jarcho

clippy_lints/src/utils/internal_lints.rs

@@ -770,6 +770,7 @@ impl<'tcx> LateLintPass<'tcx> for MatchTypeOnDiagItem {
             let diag_items = cx.tcx.diagnostic_items(ty_did.krate);
             if let Some(item_name) = diag_items.iter().find_map(|(k, v)| if *v == ty_did { Some(k) } else { None });
             then {
+                // TODO: check paths constants from external crates.
                 let cx_snippet = snippet(cx, context.span, "_");
                 let ty_snippet = snippet(cx, ty.span, "_");
 

tests/ui-internal/match_type_on_diag_item.rs

@@ -27,7 +27,7 @@ impl<'tcx> LateLintPass<'tcx> for Pass {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr) {
         let ty = cx.typeck_results().expr_ty(expr);
 
-        let _ = match_type(cx, ty, &paths::VEC);
+        let _ = match_type(cx, ty, &paths::VEC); // FIXME: Doesn't lint external paths
         let _ = match_type(cx, ty, &OPTION);
         let _ = match_type(cx, ty, &["core", "result", "Result"]);