Rollup merge of #141069 - chenyukang:yukang-fix-137486-suggest-mut, r=davidtwco

Suggest mut when possbile for temporary value dropped while borrowed

Fixes #137486

3 files changed, 81 insertions, 0 deletions

diff --git a/tests/ui/nll/sugg-mut-for-binding-issue-137486.fixed b/tests/ui/nll/sugg-mut-for-binding-issue-137486.fixed
new file mode 100644
index 00000000000..ee9d9a373de
--- /dev/null
+++ b/tests/ui/nll/sugg-mut-for-binding-issue-137486.fixed
@@ -0,0 +1,23 @@
+//@ run-rustfix
+#![allow(unused_assignments)]
+
+use std::pin::Pin;
+fn main() {
+    let mut s = String::from("hello");
+    let mut ref_s = &mut s;
+
+    let mut binding = String::from("world");
+    ref_s = &mut binding; //~ ERROR temporary value dropped while borrowed [E0716]
+
+    print!("r1 = {}", ref_s);
+
+    let mut val: u8 = 5;
+    let mut s = Pin::new(&mut val);
+    let mut ref_s = &mut s;
+
+    let mut val2: u8 = 10;
+    let mut binding = Pin::new(&mut val2);
+    ref_s = &mut binding; //~ ERROR temporary value dropped while borrowed [E0716]
+
+    print!("r1 = {}", ref_s);
+}
diff --git a/tests/ui/nll/sugg-mut-for-binding-issue-137486.rs b/tests/ui/nll/sugg-mut-for-binding-issue-137486.rs
new file mode 100644
index 00000000000..8f7ea756107
--- /dev/null
+++ b/tests/ui/nll/sugg-mut-for-binding-issue-137486.rs
@@ -0,0 +1,21 @@
+//@ run-rustfix
+#![allow(unused_assignments)]
+
+use std::pin::Pin;
+fn main() {
+    let mut s = String::from("hello");
+    let mut ref_s = &mut s;
+
+    ref_s = &mut String::from("world"); //~ ERROR temporary value dropped while borrowed [E0716]
+
+    print!("r1 = {}", ref_s);
+
+    let mut val: u8 = 5;
+    let mut s = Pin::new(&mut val);
+    let mut ref_s = &mut s;
+
+    let mut val2: u8 = 10;
+    ref_s = &mut Pin::new(&mut val2); //~ ERROR temporary value dropped while borrowed [E0716]
+
+    print!("r1 = {}", ref_s);
+}
diff --git a/tests/ui/nll/sugg-mut-for-binding-issue-137486.stderr b/tests/ui/nll/sugg-mut-for-binding-issue-137486.stderr
new file mode 100644
index 00000000000..8432725f60a
--- /dev/null
+++ b/tests/ui/nll/sugg-mut-for-binding-issue-137486.stderr
@@ -0,0 +1,37 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/sugg-mut-for-binding-issue-137486.rs:9:18
+   |
+LL |     ref_s = &mut String::from("world");
+   |                  ^^^^^^^^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
+   |                  |
+   |                  creates a temporary value which is freed while still in use
+LL |
+LL |     print!("r1 = {}", ref_s);
+   |                       ----- borrow later used here
+   |
+help: consider using a `let` binding to create a longer lived value
+   |
+LL ~     let mut binding = String::from("world");
+LL ~     ref_s = &mut binding;
+   |
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/sugg-mut-for-binding-issue-137486.rs:18:18
+   |
+LL |     ref_s = &mut Pin::new(&mut val2);
+   |                  ^^^^^^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
+   |                  |
+   |                  creates a temporary value which is freed while still in use
+LL |
+LL |     print!("r1 = {}", ref_s);
+   |                       ----- borrow later used here
+   |
+help: consider using a `let` binding to create a longer lived value
+   |
+LL ~     let mut binding = Pin::new(&mut val2);
+LL ~     ref_s = &mut binding;
+   |
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0716`.