remove support for the #[start] attribute

compiler/rustc_feature/src/builtin_attrs.rs

@@ -448,7 +448,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Entry point:
-    ungated!(start, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
 

compiler/rustc_feature/src/removed.rs

@@ -220,8 +220,9 @@ declare_features! (
     (removed, rustc_diagnostic_macros, "1.38.0", None, None),
     /// Allows identifying crates that contain sanitizer runtimes.
     (removed, sanitizer_runtime, "1.17.0", None, None),
-    (removed, simd, "1.0.0", Some(27731),
-     Some("removed in favor of `#[repr(simd)]`")),
+    (removed, simd, "1.0.0", Some(27731), Some("removed in favor of `#[repr(simd)]`")),
+    /// Allows using `#[start]` on a function indicating that it is the program entrypoint.
+    (removed, start, "1.0.0", Some(29633), Some("not portable enough and never RFC'd")),
     /// Allows `#[link(kind = "static-nobundle", ...)]`.
     (removed, static_nobundle, "1.16.0", Some(37403),
      Some(r#"subsumed by `#[link(kind = "static", modifiers = "-bundle", ...)]`"#)),

compiler/rustc_feature/src/unstable.rs

@@ -300,8 +300,6 @@ declare_features! (
     (internal, rustdoc_internals, "1.58.0", Some(90418)),
     /// Allows using the `rustdoc::missing_doc_code_examples` lint
     (unstable, rustdoc_missing_doc_code_examples, "1.31.0", Some(101730)),
-    /// Allows using `#[start]` on a function indicating that it is the program entrypoint.
-    (unstable, start, "1.0.0", Some(29633)),
     /// Allows using `#[structural_match]` which indicates that a type is structurally matchable.
     /// FIXME: Subsumed by trait `StructuralPartialEq`, cannot move to removed until a library
     /// feature with the same name exists.