add structural_init feature

Author: beepster4096

compiler/rustc_feature/src/unstable.rs

@@ -239,6 +239,8 @@ declare_features! (
     (internal, rustc_attrs, "1.0.0", None),
     /// Allows using the `#[stable]` and `#[unstable]` attributes.
     (internal, staged_api, "1.0.0", None),
+    /// FIXME: needs description and tracking issue.
+    (unstable, structural_init, "CURRENT_RUSTC_VERSION", None),
     /// Added for testing unstable lints; perma-unstable.
     (internal, test_unstable_lint, "1.60.0", None),
     /// Helps with formatting for `group_imports = "StdExternalCrate"`.

compiler/rustc_span/src/symbol.rs

@@ -2083,6 +2083,7 @@ symbols! {
         struct_field_attributes,
         struct_inherit,
         struct_variant,
+        structural_init,
         structural_match,
         structural_peq,
         sub,