From 1e2feb98ee07200542598641b4204d3458e73d18 Mon Sep 17 00:00:00 2001
From: Gus Wynn <guswynn@gmail.com>
Date: Mon, 11 Oct 2021 13:25:06 -0700
Subject: [PATCH 1/3] make must_not_suspend allow-by-default until edge cases
 are ironed out

---
 compiler/rustc_lint_defs/src/builtin.rs       |  2 +-
 src/test/ui/lint/must_not_suspend/warn.rs     |  1 +
 src/test/ui/lint/must_not_suspend/warn.stderr | 12 ++++++++----
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 5830ce26fea3f..dffb033b6b6bc 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -348,7 +348,7 @@ declare_lint! {
     /// `MutexGuard`'s)
     ///
     pub MUST_NOT_SUSPEND,
-    Warn,
+    Allow,
     "use of a `#[must_not_suspend]` value across a yield point",
 }
 
diff --git a/src/test/ui/lint/must_not_suspend/warn.rs b/src/test/ui/lint/must_not_suspend/warn.rs
index 50a696ba52322..7fdea66a23517 100644
--- a/src/test/ui/lint/must_not_suspend/warn.rs
+++ b/src/test/ui/lint/must_not_suspend/warn.rs
@@ -1,6 +1,7 @@
 // edition:2018
 // run-pass
 #![feature(must_not_suspend)]
+#![warn(must_not_suspend)]
 
 #[must_not_suspend = "You gotta use Umm's, ya know?"]
 struct Umm {
diff --git a/src/test/ui/lint/must_not_suspend/warn.stderr b/src/test/ui/lint/must_not_suspend/warn.stderr
index 24f52275b430a..42374d4acac27 100644
--- a/src/test/ui/lint/must_not_suspend/warn.stderr
+++ b/src/test/ui/lint/must_not_suspend/warn.stderr
@@ -1,19 +1,23 @@
 warning: `Umm` held across a suspend point, but should not be
-  --> $DIR/warn.rs:20:9
+  --> $DIR/warn.rs:21:9
    |
 LL |     let _guard = bar();
    |         ^^^^^^
 LL |     other().await;
    |     ------------- the value is held across this suspend point
    |
-   = note: `#[warn(must_not_suspend)]` on by default
+note: the lint level is defined here
+  --> $DIR/warn.rs:4:9
+   |
+LL | #![warn(must_not_suspend)]
+   |         ^^^^^^^^^^^^^^^^
 note: You gotta use Umm's, ya know?
-  --> $DIR/warn.rs:20:9
+  --> $DIR/warn.rs:21:9
    |
 LL |     let _guard = bar();
    |         ^^^^^^
 help: consider using a block (`{ ... }`) to shrink the value's scope, ending before the suspend point
-  --> $DIR/warn.rs:20:9
+  --> $DIR/warn.rs:21:9
    |
 LL |     let _guard = bar();
    |         ^^^^^^

From d2766a9664e6be9765a60a7adb6e1beb452da92a Mon Sep 17 00:00:00 2001
From: Gus Wynn <guswynn@gmail.com>
Date: Mon, 11 Oct 2021 14:21:58 -0700
Subject: [PATCH 2/3] ensure lint-docs build for allow-by-default
 must_not_suspend

---
 compiler/rustc_lint_defs/src/builtin.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index dffb033b6b6bc..1f1a4fbfd1bec 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -322,6 +322,7 @@ declare_lint! {
     ///
     /// ```rust
     /// #![feature(must_not_suspend)]
+    /// #![warn(must_not_suspend)]
     ///
     /// #[must_not_suspend]
     /// struct SyncThing {}

From 7b95c7be01a76b503b22cdc37caab1589d7ddc01 Mon Sep 17 00:00:00 2001
From: Gus Wynn <guswynn@gmail.com>
Date: Thu, 14 Oct 2021 10:04:21 -0700
Subject: [PATCH 3/3] add regression test for allow-by-default must_not_suspend

---
 .../ui/lint/must_not_suspend/issue-89562.rs   | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 src/test/ui/lint/must_not_suspend/issue-89562.rs

diff --git a/src/test/ui/lint/must_not_suspend/issue-89562.rs b/src/test/ui/lint/must_not_suspend/issue-89562.rs
new file mode 100644
index 0000000000000..acdb36fcdabf9
--- /dev/null
+++ b/src/test/ui/lint/must_not_suspend/issue-89562.rs
@@ -0,0 +1,19 @@
+// edition:2018
+// run-pass
+
+use std::sync::Mutex;
+
+// Copied from the issue. Allow-by-default for now, so run-pass
+pub async fn foo() {
+    let foo = Mutex::new(1);
+    let lock = foo.lock().unwrap();
+
+    // Prevent mutex lock being held across `.await` point.
+    drop(lock);
+
+    bar().await;
+}
+
+async fn bar() {}
+
+fn main() {}