Add derive_from unstable feature

Author: Kobzol

compiler/rustc_feature/src/unstable.rs

@@ -471,6 +471,8 @@ declare_features! (
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
     /// Allows deref patterns.
     (incomplete, deref_patterns, "1.79.0", Some(87121)),
+    /// Allows deriving the From trait on single-field structs.
+    (unstable, derive_from, "CURRENT_RUSTC_VERSION", Some(144889)),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.
     (unstable, doc_auto_cfg, "1.58.0", Some(43781)),
     /// Allows `#[doc(cfg(...))]`.

compiler/rustc_span/src/symbol.rs

@@ -842,6 +842,7 @@ symbols! {
         derive_const,
         derive_const_issue: "118304",
         derive_default_enum,
+        derive_from,
         derive_smart_pointer,
         destruct,
         destructuring_assignment,