improve const eq functionality in patterns

Author: xacrimon

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

@@ -17,6 +17,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::DefId;
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Span, Symbol, sym};
+use rustc_trait_selection::infer::InferCtxtExt;
 use tracing::{debug, instrument};
 
 use crate::builder::Builder;
@@ -450,7 +451,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             (_, expect) = coerce(expect_ty, expect, *elem_ty);
         }
 
-        // Figure out the type on which we are calling `PartialEq`. This involves an extra wrapping
+        // Figure out the type we are searching for traits against. This involves an extra wrapping
         // reference: we can only compare two `&T`, and then compare_ty will be `T`.
         // Make sure that we do *not* call any user-defined code here.
         // The only types that can end up here are string and byte literals,
@@ -466,10 +467,20 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             _ => span_bug!(source_info.span, "invalid type for non-scalar compare: {}", ty),
         };
 
-        let eq_def_id =
+        let mut cmp_trait_def_id =
             self.tcx.require_lang_item(LangItem::MatchLoweredCmp, Some(source_info.span));
-        let method = trait_method(self.tcx, eq_def_id, sym::do_match, [compare_ty, compare_ty]);
 
+        let has_pattern_eq = self
+            .infcx
+            .type_implements_trait(cmp_trait_def_id, [compare_ty], self.param_env)
+            .must_apply_modulo_regions();
+        if !has_pattern_eq {
+            cmp_trait_def_id =
+                self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span));
+        }
+
+        let method =
+            trait_method(self.tcx, cmp_trait_def_id, sym::do_match, [compare_ty, compare_ty]);
         let bool_ty = self.tcx.types.bool;
         let eq_result = self.temp(bool_ty, source_info.span);
         let eq_block = self.cfg.start_new_block();

library/core/src/cmp/pattern.rs

@@ -8,15 +8,28 @@ where
     fn do_match(&self, other: &Rhs) -> bool;
 }
 
-// other types?
+// TODO: tuples, arrays?
+
+macro_rules ! impl_match_lowered_cmp_for_primitive {
+    ($($t:ty),*) => {
+        $(
+            impl const MatchLoweredCmp for $t {
+                fn do_match(&self, other: &Self) -> bool {
+                    *self == *other
+                }
+            }
+        )*
+    };
+}
 
-impl const MatchLoweredCmp for u8 {
-    fn do_match(&self, other: &Self) -> bool {
-        *self == *other
-    }
+impl_match_lowered_cmp_for_primitive! {
+    (), bool, char,
+    u8, u16, u32, u64, u128, usize,
+    i8, i16, i32, i64, i128, isize,
+    f32, f64
 }
 
-// shouldn't be const
+// note: this wasn't possible before
 impl const MatchLoweredCmp for str {
     #[rustc_allow_const_fn_unstable(const_trait_impl)]
     fn do_match(&self, other: &Self) -> bool {
@@ -47,20 +60,3 @@ where
         true
     }
 }
-
-//impl<const N:usize, T> const MatchLoweredCmp for [T; N] where T: ~const MatchLoweredCmp {
-//    #[rustc_allow_const_fn_unstable(const_trait_impl)]
-//    fn do_match(&self, other: &Self) -> bool {
-//        let mut i = 0;
-//
-//        while i < N {
-//            if <T as MatchLoweredCmp>::do_match(&self[i], &other[i]) == false {
-//                return false;
-//            }
-//
-//            i += 1;
-//        }
-//
-//        true
-//    }
-//}