add lang item

Author: xacrimon

compiler/rustc_hir/src/lang_items.rs

@@ -417,6 +417,9 @@ language_item_table! {
 
     String,                  sym::String,              string,                     Target::Struct,         GenericRequirement::None;
     CStr,                    sym::CStr,                c_str,                      Target::Struct,         GenericRequirement::None;
+
+    // FIXME(xacrimon): Used for lowering of match/if let statements. will made obsolete by const PartialEq.
+    MatchLoweredCmp,         sym::MatchLoweredCmp,     match_lowered_cmp,          Target::Trait,          GenericRequirement::None;
 }
 
 pub enum GenericRequirement {

compiler/rustc_mir_build/src/builder/matches/util.rs

@@ -229,3 +229,8 @@ pub(crate) fn ref_pat_borrow_kind(ref_mutability: Mutability) -> BorrowKind {
         Mutability::Not => BorrowKind::Shared,
     }
 }
+
+#[lang = "MatchLoweredCmp"]
+pub trait MatchLoweredCmp {
+    fn same_as(&self, other: &Self) -> bool;
+}

compiler/rustc_mir_build/src/lib.rs

@@ -3,11 +3,13 @@
 // tidy-alphabetical-start
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
+#![allow(internal_features)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(try_blocks)]
+#![feature(lang_items)]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
 

compiler/rustc_span/src/symbol.rs

@@ -267,6 +267,7 @@ symbols! {
         LintDiagnostic,
         LintPass,
         LocalKey,
+        MatchLoweredCmp,
         Mutex,
         MutexGuard,
         N,