Rollup merge of #119704 - chenyukang:yukang-fix-let_underscore, r=Nilstrieb

Fix two variable binding issues in lint let_underscore

Fixes #119696
Fixes #119697

4 files changed, 101 insertions, 0 deletions

diff --git a/tests/ui/lint/let_underscore/issue-119696-err-on-fn.rs b/tests/ui/lint/let_underscore/issue-119696-err-on-fn.rs
new file mode 100644
index 00000000000..8e15b4da35a
--- /dev/null
+++ b/tests/ui/lint/let_underscore/issue-119696-err-on-fn.rs
@@ -0,0 +1,21 @@
+// edition: 2021
+
+#![deny(let_underscore_drop)]
+fn main() {
+    let _ = foo(); //~ ERROR non-binding let on a type that implements `Drop`
+}
+
+async fn from_config(_: Config) {}
+
+async fn foo() {
+    from_config(Config {
+        nickname: None,
+        ..Default::default()
+    })
+    .await;
+}
+
+#[derive(Default)]
+struct Config {
+    nickname: Option<Box<u8>>,
+}
diff --git a/tests/ui/lint/let_underscore/issue-119696-err-on-fn.stderr b/tests/ui/lint/let_underscore/issue-119696-err-on-fn.stderr
new file mode 100644
index 00000000000..86e521580b8
--- /dev/null
+++ b/tests/ui/lint/let_underscore/issue-119696-err-on-fn.stderr
@@ -0,0 +1,22 @@
+error: non-binding let on a type that implements `Drop`
+  --> $DIR/issue-119696-err-on-fn.rs:5:5
+   |
+LL |     let _ = foo();
+   |     ^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-119696-err-on-fn.rs:3:9
+   |
+LL | #![deny(let_underscore_drop)]
+   |         ^^^^^^^^^^^^^^^^^^^
+help: consider binding to an unused variable to avoid immediately dropping the value
+   |
+LL |     let _unused = foo();
+   |         ~~~~~~~
+help: consider immediately dropping the value
+   |
+LL |     drop(foo());
+   |     ~~~~~     +
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/lint/let_underscore/issue-119697-extra-let.rs b/tests/ui/lint/let_underscore/issue-119697-extra-let.rs
new file mode 100644
index 00000000000..1dc80a123f6
--- /dev/null
+++ b/tests/ui/lint/let_underscore/issue-119697-extra-let.rs
@@ -0,0 +1,21 @@
+#![deny(let_underscore_drop)]
+#![feature(type_alias_impl_trait)]
+
+pub struct Foo {
+    /// This type must have nontrivial drop glue
+    field: String,
+}
+
+pub type Tait = impl Sized;
+
+pub fn ice_cold(beverage: Tait) {
+    // Must destructure at least one field of `Foo`
+    let Foo { field } = beverage;
+    // boom
+    _ = field; //~ ERROR non-binding let on a type that implements `Drop`
+
+    let _ = field; //~ ERROR non-binding let on a type that implements `Drop`
+}
+
+
+pub fn main() {}
diff --git a/tests/ui/lint/let_underscore/issue-119697-extra-let.stderr b/tests/ui/lint/let_underscore/issue-119697-extra-let.stderr
new file mode 100644
index 00000000000..16df2c720ea
--- /dev/null
+++ b/tests/ui/lint/let_underscore/issue-119697-extra-let.stderr
@@ -0,0 +1,37 @@
+error: non-binding let on a type that implements `Drop`
+  --> $DIR/issue-119697-extra-let.rs:15:5
+   |
+LL |     _ = field;
+   |     ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-119697-extra-let.rs:1:9
+   |
+LL | #![deny(let_underscore_drop)]
+   |         ^^^^^^^^^^^^^^^^^^^
+help: consider binding to an unused variable to avoid immediately dropping the value
+   |
+LL |     let _unused = field;
+   |     ~~~~~~~~~~~
+help: consider immediately dropping the value
+   |
+LL |     drop(field);
+   |     ~~~~~     +
+
+error: non-binding let on a type that implements `Drop`
+  --> $DIR/issue-119697-extra-let.rs:17:5
+   |
+LL |     let _ = field;
+   |     ^^^^^^^^^^^^^^
+   |
+help: consider binding to an unused variable to avoid immediately dropping the value
+   |
+LL |     let _unused = field;
+   |         ~~~~~~~
+help: consider immediately dropping the value
+   |
+LL |     drop(field);
+   |     ~~~~~     +
+
+error: aborting due to 2 previous errors
+