Add test of deprecated type in From impl

    error: use of deprecated struct `test_deprecated::DeprecatedStruct`
      --> tests/test_lints.rs:73:13
       |
    73 |             DeprecatedStruct,
       |             ^^^^^^^^^^^^^^^^
       |
    note: the lint level is defined here
      --> tests/test_lints.rs:39:13
       |
    39 |     #![deny(deprecated)]
       |             ^^^^^^^^^^

Author: dtolnay

tests/test_lints.rs

@@ -64,6 +64,16 @@ fn test_deprecated() {
         Variant,
     }
 
+    #[derive(Error, Debug)]
+    pub enum DeprecatedFrom {
+        #[error(transparent)]
+        Variant(
+            #[from]
+            #[allow(deprecated)]
+            DeprecatedStruct,
+        ),
+    }
+
     #[allow(deprecated)]
     let _: DeprecatedStruct;
     #[allow(deprecated)]