From edee23ee25d813547587fdd6bcd3677606839fad Mon Sep 17 00:00:00 2001
From: Matthew Jasper <mjjasper1@gmail.com>
Date: Sat, 28 Dec 2019 15:50:06 +0000
Subject: [PATCH] Avoid unnecessary opaque type errors in borrowck

---
 src/librustc_mir/borrow_check/mod.rs | 3 +++
 src/librustc_mir/borrow_check/nll.rs | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/src/librustc_mir/borrow_check/mod.rs b/src/librustc_mir/borrow_check/mod.rs
index 1843d4bf72d..da9bdc8b4b0 100644
--- a/src/librustc_mir/borrow_check/mod.rs
+++ b/src/librustc_mir/borrow_check/mod.rs
@@ -136,6 +136,9 @@ fn do_mir_borrowck<'a, 'tcx>(
 
     // Gather the upvars of a closure, if any.
     let tables = tcx.typeck_tables_of(def_id);
+    if tables.tainted_by_errors {
+        infcx.set_tainted_by_errors();
+    }
     let upvars: Vec<_> = tables
         .upvar_list
         .get(&def_id)
diff --git a/src/librustc_mir/borrow_check/nll.rs b/src/librustc_mir/borrow_check/nll.rs
index e4e5fe35d7f..4c1ee9582c1 100644
--- a/src/librustc_mir/borrow_check/nll.rs
+++ b/src/librustc_mir/borrow_check/nll.rs
@@ -282,6 +282,11 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     let (closure_region_requirements, nll_errors) =
         regioncx.solve(infcx, &body, def_id, polonius_output.clone());
 
+    if !nll_errors.is_empty() {
+        // Suppress unhelpful extra errors in `infer_opaque_types`.
+        infcx.set_tainted_by_errors();
+    }
+
     let remapped_opaque_tys = regioncx.infer_opaque_types(&infcx, opaque_type_values, body.span);
 
     NllOutput {