Auto merge of #55635 - oli-obk:min_const_unsafe_fn, r=nikomatsakis

Allow calling `const unsafe fn` in `const fn` behind a feature gate

cc #55607

r? @Centril

1 files changed, 28 insertions, 4 deletions

diff --git a/src/librustc_data_structures/indexed_vec.rs b/src/librustc_data_structures/indexed_vec.rs
index a59bf9d530c..6522dbe1179 100644
--- a/src/librustc_data_structures/indexed_vec.rs
+++ b/src/librustc_data_structures/indexed_vec.rs
@@ -98,12 +98,18 @@ macro_rules! newtype_index {
      @max          [$max:expr]
      @vis          [$v:vis]
      @debug_format [$debug_format:tt]) => (
-        #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, $($derives),*)]
+        #[derive(Copy, PartialEq, Eq, Hash, PartialOrd, Ord, $($derives),*)]
         #[rustc_layout_scalar_valid_range_end($max)]
         $v struct $type {
             private: u32
         }
 
+        impl Clone for $type {
+            fn clone(&self) -> Self {
+                *self
+            }
+        }
+
         impl $type {
             $v const MAX_AS_U32: u32 = $max;
 
@@ -145,7 +151,7 @@ macro_rules! newtype_index {
 
             #[inline]
             $v const unsafe fn from_u32_unchecked(value: u32) -> Self {
-                $type { private: value }
+                unsafe { $type { private: value } }
             }
 
             /// Extract value of this index as an integer.
@@ -328,12 +334,13 @@ macro_rules! newtype_index {
                    derive [$($derives:ident,)+]
                    $($tokens:tt)*) => (
         newtype_index!(
-            @derives      [$($derives,)+ RustcDecodable, RustcEncodable,]
+            @derives      [$($derives,)+ RustcEncodable,]
             @type         [$type]
             @max          [$max]
             @vis          [$v]
             @debug_format [$debug_format]
                           $($tokens)*);
+        newtype_index!(@decodable $type);
     );
 
     // The case where no derives are added, but encodable is overridden. Don't
@@ -360,12 +367,29 @@ macro_rules! newtype_index {
      @debug_format [$debug_format:tt]
                    $($tokens:tt)*) => (
         newtype_index!(
-            @derives      [RustcDecodable, RustcEncodable,]
+            @derives      [RustcEncodable,]
             @type         [$type]
             @max          [$max]
             @vis          [$v]
             @debug_format [$debug_format]
                           $($tokens)*);
+        newtype_index!(@decodable $type);
+    );
+
+    (@decodable $type:ident) => (
+        impl $type {
+            fn __decodable__impl__hack() {
+                mod __more_hacks_because__self_doesnt_work_in_functions {
+                    extern crate serialize;
+                    use self::serialize::{Decodable, Decoder};
+                    impl Decodable for super::$type {
+                        fn decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
+                            d.read_u32().map(Self::from)
+                        }
+                    }
+                }
+            }
+        }
     );
 
     // Rewrite final without comma to one that includes comma