From 500503b16ca9f72a44028e27c1cc2fa76be49085 Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Sun, 16 May 2021 22:26:57 -0400
Subject: [PATCH] Suppress spurious errors inside `async fn`

Fixes #73741
---
 .../src/check/generator_interior.rs           | 30 +++++++++++++------
 .../ui/async-await/issue-73741-type-err.rs    | 14 +++++++++
 .../async-await/issue-73741-type-err.stderr   | 11 +++++++
 3 files changed, 46 insertions(+), 9 deletions(-)
 create mode 100644 src/test/ui/async-await/issue-73741-type-err.rs
 create mode 100644 src/test/ui/async-await/issue-73741-type-err.stderr

diff --git a/compiler/rustc_typeck/src/check/generator_interior.rs b/compiler/rustc_typeck/src/check/generator_interior.rs
index e40aa914858..5f26e701c0a 100644
--- a/compiler/rustc_typeck/src/check/generator_interior.rs
+++ b/compiler/rustc_typeck/src/check/generator_interior.rs
@@ -89,19 +89,31 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
             if let Some((unresolved_type, unresolved_type_span)) =
                 self.fcx.unresolved_type_vars(&ty)
             {
-                let note = format!(
-                    "the type is part of the {} because of this {}",
-                    self.kind, yield_data.source
-                );
-
                 // If unresolved type isn't a ty_var then unresolved_type_span is None
                 let span = self
                     .prev_unresolved_span
                     .unwrap_or_else(|| unresolved_type_span.unwrap_or(source_span));
-                self.fcx
-                    .need_type_info_err_in_generator(self.kind, span, unresolved_type)
-                    .span_note(yield_data.span, &*note)
-                    .emit();
+
+                // If we encounter an int/float variable, then inference fallback didn't
+                // finish due to some other error. Don't emit spurious additional errors.
+                if let ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) =
+                    unresolved_type.kind()
+                {
+                    self.fcx
+                        .tcx
+                        .sess
+                        .delay_span_bug(span, &format!("Encountered var {:?}", unresolved_type));
+                } else {
+                    let note = format!(
+                        "the type is part of the {} because of this {}",
+                        self.kind, yield_data.source
+                    );
+
+                    self.fcx
+                        .need_type_info_err_in_generator(self.kind, span, unresolved_type)
+                        .span_note(yield_data.span, &*note)
+                        .emit();
+                }
             } else {
                 // Insert the type into the ordered set.
                 let scope_span = scope.map(|s| s.span(self.fcx.tcx, self.region_scope_tree));
diff --git a/src/test/ui/async-await/issue-73741-type-err.rs b/src/test/ui/async-await/issue-73741-type-err.rs
new file mode 100644
index 00000000000..c5b9e34edf7
--- /dev/null
+++ b/src/test/ui/async-await/issue-73741-type-err.rs
@@ -0,0 +1,14 @@
+// edition:2018
+//
+// Regression test for issue #73741
+// Ensures that we don't emit spurious errors when
+// a type error ocurrs in an `async fn`
+
+async fn weird() {
+    1 = 2; //~ ERROR invalid left-hand side
+
+    let mut loop_count = 0;
+    async {}.await
+}
+
+fn main() {}
diff --git a/src/test/ui/async-await/issue-73741-type-err.stderr b/src/test/ui/async-await/issue-73741-type-err.stderr
new file mode 100644
index 00000000000..0b5343a98cf
--- /dev/null
+++ b/src/test/ui/async-await/issue-73741-type-err.stderr
@@ -0,0 +1,11 @@
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/issue-73741-type-err.rs:8:7
+   |
+LL |     1 = 2;
+   |     - ^
+   |     |
+   |     cannot assign to this expression
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0070`.