Ungate improved slice patterns diagnostics

Author: Nadrieril

src/librustc_mir/hair/pattern/_match.rs

@@ -1209,19 +1209,10 @@ impl<'tcx> Constructor<'tcx> {
             }
             VarLenSlice(prefix_len, _suffix_len) => match ty.kind {
                 ty::Slice(ty) | ty::Array(ty, _) => {
-                    if cx.tcx.features().slice_patterns {
-                        let prefix = pats.by_ref().take(prefix_len as usize).collect();
-                        let suffix = pats.collect();
-                        let wild = Pat { ty, span: DUMMY_SP, kind: Box::new(PatKind::Wild) };
-                        PatKind::Slice { prefix, slice: Some(wild), suffix }
-                    } else {
-                        // We don't want to output a variable-length slice pattern if the
-                        // slice_patterns feature is not enabled.
-                        // The constructor covers infinitely many slice lengths, but for diagnostic
-                        // purposes it is correct to return only some examples of non-covered
-                        // patterns. So we just return the smallest length pattern here.
-                        PatKind::Slice { prefix: pats.collect(), slice: None, suffix: vec![] }
-                    }
+                    let prefix = pats.by_ref().take(prefix_len as usize).collect();
+                    let suffix = pats.collect();
+                    let wild = Pat { ty, span: DUMMY_SP, kind: Box::new(PatKind::Wild) };
+                    PatKind::Slice { prefix, slice: Some(wild), suffix }
                 }
                 _ => bug!("bad slice pattern {:?} {:?}", self, ty),
             },

src/test/ui/consts/const_let_refutable.stderr

@@ -1,8 +1,8 @@
-error[E0005]: refutable pattern in function argument: `&[]`, `&[_]` and `&[_, _, _]` not covered
+error[E0005]: refutable pattern in function argument: `&[]`, `&[_]` and `&[_, _, _, ..]` not covered
   --> $DIR/const_let_refutable.rs:3:16
    |
 LL | const fn slice([a, b]: &[i32]) -> i32 {
-   |                ^^^^^^ patterns `&[]`, `&[_]` and `&[_, _, _]` not covered
+   |                ^^^^^^ patterns `&[]`, `&[_]` and `&[_, _, _, ..]` not covered
 
 error[E0723]: can only call other `const fn` within a `const fn`, but `const <&i32 as std::ops::Add>::add` is not stable as `const fn`
   --> $DIR/const_let_refutable.rs:4:5

src/test/ui/pattern/usefulness/match-byte-array-patterns-2.stderr

@@ -6,11 +6,11 @@ LL |     match buf {
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[]` not covered
+error[E0004]: non-exhaustive patterns: `&[..]` not covered
   --> $DIR/match-byte-array-patterns-2.rs:10:11
    |
 LL |     match buf {
-   |           ^^^ pattern `&[]` not covered
+   |           ^^^ pattern `&[..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 

src/test/ui/uninhabited/uninhabited-matches-feature-gated.stderr

@@ -30,11 +30,11 @@ LL |     let _ = match x {};
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[_]` not covered
+error[E0004]: non-exhaustive patterns: `&[_, ..]` not covered
   --> $DIR/uninhabited-matches-feature-gated.rs:21:19
    |
 LL |     let _ = match x {
-   |                   ^ pattern `&[_]` not covered
+   |                   ^ pattern `&[_, ..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms