Remove enum_from_u32.

It's a macro that just creates an enum with a `from_u32` method. It has
two arms. One is unused and the other has a single use.

This commit inlines that single use and removes the whole macro. This
increases readability because we don't have two different macros
interacting (`enum_from_u32` and `language_item_table`).

Author: nnethercote

compiler/rustc_data_structures/src/lib.rs

@@ -62,7 +62,6 @@ pub mod fx;
 pub mod graph;
 pub mod intern;
 pub mod jobserver;
-pub mod macros;
 pub mod marker;
 pub mod memmap;
 pub mod obligation_forest;

compiler/rustc_data_structures/src/macros.rs

@@ -55,17 +55,22 @@ macro_rules! language_item_table {
     (
         $( $(#[$attr:meta])* $variant:ident, $module:ident :: $name:ident, $method:ident, $target:expr, $generics:expr; )*
     ) => {
+        /// A representation of all the valid lang items in Rust.
+        #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
+        pub enum LangItem {
+            $(
+                #[doc = concat!("The `", stringify!($name), "` lang item.")]
+                $(#[$attr])*
+                $variant,
+            )*
+        }
 
-        rustc_data_structures::enum_from_u32! {
-            /// A representation of all the valid lang items in Rust.
-            #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
-            pub enum LangItem {
-                $(
-                    #[doc = concat!("The `", stringify!($name), "` lang item.")]
-                    ///
-                    $(#[$attr])*
-                    $variant,
-                )*
+        impl LangItem {
+            pub fn from_u32(u: u32) -> Option<LangItem> {
+                $(if u == LangItem::$variant as u32 {
+                    return Some(LangItem::$variant)
+                })*
+                None
             }
         }