From 276734d6a4997088b6d2e7416f5d4c07b4c8acf5 Mon Sep 17 00:00:00 2001
From: David Ross <daboross@daboross.net>
Date: Sat, 1 Feb 2020 18:04:07 -0800
Subject: [PATCH] Fix 59191

This adds an explicit error for when macros replace the crate root with
a non-module item.
---
 src/librustc_expand/expand.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/librustc_expand/expand.rs b/src/librustc_expand/expand.rs
index ea459064b09..1aa4f11a130 100644
--- a/src/librustc_expand/expand.rs
+++ b/src/librustc_expand/expand.rs
@@ -363,7 +363,15 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 krate.attrs = vec![];
                 krate.module = ast::Mod { inner: orig_mod_span, items: vec![], inline: true };
             }
-            _ => unreachable!(),
+            Some(ast::Item { span, kind, .. }) => {
+                self.cx.span_fatal(
+                    span,
+                    &format!(
+                        "expected crate top-level item to be a module after macro expansion, found a {}",
+                        kind.descriptive_variant()
+                    ),
+                );
+            }
         };
         self.cx.trace_macros_diag();
         krate