Add test for #8855

3 files changed, 55 insertions, 1 deletions

diff --git a/tests/ui/format_args.fixed b/tests/ui/format_args.fixed
index 4322891db76..e07cae70277 100644
--- a/tests/ui/format_args.fixed
+++ b/tests/ui/format_args.fixed
@@ -122,3 +122,27 @@ fn issue8643(vendor_id: usize, product_id: usize, name: &str) {
         name
     );
 }
+
+// https://github.com/rust-lang/rust-clippy/issues/8855
+mod issue_8855 {
+    #![allow(dead_code)]
+
+    struct A {}
+
+    impl std::fmt::Display for A {
+        fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+            write!(f, "test")
+        }
+    }
+
+    fn main() {
+        let a = A {};
+        let b = A {};
+
+        let x = format!("{} {}", a, b);
+        dbg!(x);
+
+        let x = format!("{:>6} {:>6}", a, b.to_string());
+        dbg!(x);
+    }
+}
diff --git a/tests/ui/format_args.rs b/tests/ui/format_args.rs
index 61ad04612cd..86e66bce2c5 100644
--- a/tests/ui/format_args.rs
+++ b/tests/ui/format_args.rs
@@ -122,3 +122,27 @@ fn issue8643(vendor_id: usize, product_id: usize, name: &str) {
         name
     );
 }
+
+// https://github.com/rust-lang/rust-clippy/issues/8855
+mod issue_8855 {
+    #![allow(dead_code)]
+
+    struct A {}
+
+    impl std::fmt::Display for A {
+        fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+            write!(f, "test")
+        }
+    }
+
+    fn main() {
+        let a = A {};
+        let b = A {};
+
+        let x = format!("{} {}", a, b.to_string());
+        dbg!(x);
+
+        let x = format!("{:>6} {:>6}", a, b.to_string());
+        dbg!(x);
+    }
+}
diff --git a/tests/ui/format_args.stderr b/tests/ui/format_args.stderr
index 0aca1c1a0df..e69999cc9d0 100644
--- a/tests/ui/format_args.stderr
+++ b/tests/ui/format_args.stderr
@@ -126,5 +126,11 @@ error: `to_string` applied to a type that implements `Display` in `println!` arg
 LL |     println!("{foo}{bar}", bar = "bar", foo = "foo".to_string());
    |                                                    ^^^^^^^^^^^^ help: remove this
 
-error: aborting due to 21 previous errors
+error: `to_string` applied to a type that implements `Display` in `format!` args
+  --> $DIR/format_args.rs:142:38
+   |
+LL |         let x = format!("{} {}", a, b.to_string());
+   |                                      ^^^^^^^^^^^^ help: remove this
+
+error: aborting due to 22 previous errors