Rollup merge of #132708 - estebank:const-as-binding, r=Nadrieril

Point at `const` definition when used instead of a binding in a `let` statement

Modify `PatKind::InlineConstant` to be `ExpandedConstant` standing in not only for inline `const` blocks but also for `const` items. This allows us to track named `const`s used in patterns when the pattern is a single binding. When we detect that there is a refutable pattern involving a `const` that could have been a binding instead, we point at the `const` item, and suggest renaming. We do this for both `let` bindings and `match` expressions missing a catch-all arm if there's at least one single binding pattern referenced.

After:

```
error[E0005]: refutable pattern in local binding
  --> $DIR/bad-pattern.rs:19:13
   |
LL |     const PAT: u32 = 0;
   |     -------------- missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
...
LL |         let PAT = v1;
   |             ^^^ pattern `1_u32..=u32::MAX` not covered
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `u32`
help: introduce a variable instead
   |
LL |         let PAT_var = v1;
   |             ~~~~~~~
```

Before:

```
error[E0005]: refutable pattern in local binding
  --> $DIR/bad-pattern.rs:19:13
   |
LL |         let PAT = v1;
   |             ^^^
   |             |
   |             pattern `1_u32..=u32::MAX` not covered
   |             missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
   |             help: introduce a variable instead: `PAT_var`
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `u32`
```

CC #132582.

compiler/rustc_middle/src/thir.rs

@@ -645,7 +645,7 @@ impl<'tcx> Pat<'tcx> {
             | Binding { subpattern: Some(subpattern), .. }
             | Deref { subpattern }
             | DerefPattern { subpattern, .. }
-            | InlineConstant { subpattern, .. } => subpattern.walk_(it),
+            | ExpandedConstant { subpattern, .. } => subpattern.walk_(it),
             Leaf { subpatterns } | Variant { subpatterns, .. } => {
                 subpatterns.iter().for_each(|field| field.pattern.walk_(it))
             }
@@ -788,12 +788,17 @@ pub enum PatKind<'tcx> {
         value: mir::Const<'tcx>,
     },
 
-    /// Inline constant found while lowering a pattern.
+    /// Pattern obtained by converting a constant (inline or named) to its pattern
-    InlineConstant {
+    /// representation using `const_to_pat`.
-        /// [LocalDefId] of the constant, we need this so that we have a
+    ExpandedConstant {
+        /// [DefId] of the constant, we need this so that we have a
         /// reference that can be used by unsafety checking to visit nested
-        /// unevaluated constants.
+        /// unevaluated constants and for diagnostics. If the `DefId` doesn't
-        def: LocalDefId,
+        /// correspond to a local crate, it points at the `const` item.
+        def_id: DefId,
+        /// If `false`, then `def_id` points at a `const` item, otherwise it
+        /// corresponds to a local inline const.
+        is_inline: bool,
         /// If the inline constant is used in a range pattern, this subpattern
         /// represents the range (if both ends are inline constants, there will
         /// be multiple InlineConstant wrappers).

compiler/rustc_middle/src/thir/visit.rs

@@ -247,7 +247,7 @@ pub fn walk_pat<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
             }
         }
         Constant { value: _ } => {}
-        InlineConstant { def: _, subpattern } => visitor.visit_pat(subpattern),
+        ExpandedConstant { def_id: _, is_inline: _, subpattern } => visitor.visit_pat(subpattern),
         Range(_) => {}
         Slice { prefix, slice, suffix } | Array { prefix, slice, suffix } => {
             for subpattern in prefix.iter() {

compiler/rustc_mir_build/src/build/custom/parse/instruction.rs

@@ -144,12 +144,20 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
         let mut targets = Vec::new();
         for arm in rest {
             let arm = &self.thir[*arm];
-            let PatKind::Constant { value } = arm.pattern.kind else {
+            let value = match arm.pattern.kind {
+                PatKind::Constant { value } => value,
+                PatKind::ExpandedConstant { ref subpattern, def_id: _, is_inline: false }
+                    if let PatKind::Constant { value } = subpattern.kind =>
+                {
+                    value
+                }
+                _ => {
                     return Err(ParseError {
                         span: arm.pattern.span,
                         item_description: format!("{:?}", arm.pattern.kind),
                         expected: "constant pattern".to_string(),
                     });
+                }
             };
             values.push(value.eval_bits(self.tcx, self.typing_env));
             targets.push(self.parse_block(arm.body)?);

compiler/rustc_mir_build/src/build/matches/match_pair.rs

@@ -162,7 +162,11 @@ impl<'pat, 'tcx> MatchPairTree<'pat, 'tcx> {
                 TestCase::Irrefutable { ascription: None, binding }
             }
 
-            PatKind::InlineConstant { subpattern: ref pattern, def, .. } => {
+            PatKind::ExpandedConstant { subpattern: ref pattern, def_id: _, is_inline: false } => {
+                subpairs.push(MatchPairTree::for_pattern(place_builder, pattern, cx));
+                default_irrefutable()
+            }
+            PatKind::ExpandedConstant { subpattern: ref pattern, def_id, is_inline: true } => {
                 // Apply a type ascription for the inline constant to the value at `match_pair.place`
                 let ascription = place.map(|source| {
                     let span = pattern.span;
@@ -173,7 +177,7 @@ impl<'pat, 'tcx> MatchPairTree<'pat, 'tcx> {
                     })
                     .args;
                     let user_ty = cx.infcx.canonicalize_user_type_annotation(ty::UserType::TypeOf(
-                        def.to_def_id(),
+                        def_id,
                         ty::UserArgs { args, user_self_ty: None },
                     ));
                     let annotation = ty::CanonicalUserTypeAnnotation {

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -917,7 +917,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 self.visit_primary_bindings(subpattern, subpattern_user_ty, f)
             }
 
-            PatKind::InlineConstant { ref subpattern, .. } => {
+            PatKind::ExpandedConstant { ref subpattern, .. } => {
                 self.visit_primary_bindings(subpattern, pattern_user_ty, f)
             }
 

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -332,7 +332,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 PatKind::Wild |
                 // these just wrap other patterns, which we recurse on below.
                 PatKind::Or { .. } |
-                PatKind::InlineConstant { .. } |
+                PatKind::ExpandedConstant { .. } |
                 PatKind::AscribeUserType { .. } |
                 PatKind::Error(_) => {}
             }
@@ -386,8 +386,12 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 visit::walk_pat(self, pat);
                 self.inside_adt = old_inside_adt;
             }
-            PatKind::InlineConstant { def, .. } => {
+            PatKind::ExpandedConstant { def_id, is_inline, .. } => {
-                self.visit_inner_body(*def);
+                if let Some(def) = def_id.as_local()
+                    && *is_inline
+                {
+                    self.visit_inner_body(def);
+                }
                 visit::walk_pat(self, pat);
             }
             _ => {

compiler/rustc_mir_build/src/errors.rs

@@ -860,8 +860,10 @@ pub(crate) struct PatternNotCovered<'s, 'tcx> {
     pub(crate) uncovered: Uncovered,
     #[subdiagnostic]
     pub(crate) inform: Option<Inform>,
+    #[label(mir_build_confused)]
+    pub(crate) interpreted_as_const: Option<Span>,
     #[subdiagnostic]
-    pub(crate) interpreted_as_const: Option<InterpretedAsConst>,
+    pub(crate) interpreted_as_const_sugg: Option<InterpretedAsConst>,
     #[subdiagnostic]
     pub(crate) adt_defined_here: Option<AdtDefinedHere<'tcx>>,
     #[note(mir_build_privately_uninhabited)]
@@ -911,9 +913,9 @@ impl<'tcx> Subdiagnostic for AdtDefinedHere<'tcx> {
 #[suggestion(
     mir_build_interpreted_as_const,
     code = "{variable}_var",
-    applicability = "maybe-incorrect"
+    applicability = "maybe-incorrect",
+    style = "verbose"
 )]
-#[label(mir_build_confused)]
 pub(crate) struct InterpretedAsConst {
     #[primary_span]
     pub(crate) span: Span,

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -678,8 +678,25 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
         let mut let_suggestion = None;
         let mut misc_suggestion = None;
         let mut interpreted_as_const = None;
+        let mut interpreted_as_const_sugg = None;
 
-        if let PatKind::Constant { .. }
+        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. }
+        | PatKind::AscribeUserType {
+            subpattern:
+                box Pat { kind: PatKind::ExpandedConstant { def_id, is_inline: false, .. }, .. },
+            ..
+        } = pat.kind
+            && let DefKind::Const = self.tcx.def_kind(def_id)
+            && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(pat.span)
+            // We filter out paths with multiple path::segments.
+            && snippet.chars().all(|c| c.is_alphanumeric() || c == '_')
+        {
+            let span = self.tcx.def_span(def_id);
+            let variable = self.tcx.item_name(def_id).to_string();
+            // When we encounter a constant as the binding name, point at the `const` definition.
+            interpreted_as_const = Some(span);
+            interpreted_as_const_sugg = Some(InterpretedAsConst { span: pat.span, variable });
+        } else if let PatKind::Constant { .. }
         | PatKind::AscribeUserType {
             subpattern: box Pat { kind: PatKind::Constant { .. }, .. },
             ..
@@ -692,9 +709,6 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
                 misc_suggestion = Some(MiscPatternSuggestion::AttemptedIntegerLiteral {
                     start_span: pat.span.shrink_to_lo(),
                 });
-            } else if snippet.chars().all(|c| c.is_alphanumeric() || c == '_') {
-                interpreted_as_const =
-                    Some(InterpretedAsConst { span: pat.span, variable: snippet });
             }
         }
 
@@ -743,6 +757,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             uncovered: Uncovered::new(pat.span, &cx, witnesses),
             inform,
             interpreted_as_const,
+            interpreted_as_const_sugg,
             witness_1_is_privately_uninhabited,
             _p: (),
             pattern_ty,
@@ -1112,13 +1127,13 @@ fn report_non_exhaustive_match<'p, 'tcx>(
             if ty.is_ptr_sized_integral() {
                 if ty.inner() == cx.tcx.types.usize {
                     err.note(format!(
-                        "`{ty}` does not have a fixed maximum value, so half-open ranges are necessary to match \
+                        "`{ty}` does not have a fixed maximum value, so half-open ranges are \
-                             exhaustively",
+                         necessary to match exhaustively",
                     ));
                 } else if ty.inner() == cx.tcx.types.isize {
                     err.note(format!(
-                        "`{ty}` does not have fixed minimum and maximum values, so half-open ranges are necessary to match \
+                        "`{ty}` does not have fixed minimum and maximum values, so half-open \
-                             exhaustively",
+                         ranges are necessary to match exhaustively",
                     ));
                 }
             } else if ty.inner() == cx.tcx.types.str_ {
@@ -1139,6 +1154,31 @@ fn report_non_exhaustive_match<'p, 'tcx>(
         }
     }
 
+    for &arm in arms {
+        let arm = &thir.arms[arm];
+        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. } = arm.pattern.kind
+            && let Ok(snippet) = cx.tcx.sess.source_map().span_to_snippet(arm.pattern.span)
+            // We filter out paths with multiple path::segments.
+            && snippet.chars().all(|c| c.is_alphanumeric() || c == '_')
+        {
+            let const_name = cx.tcx.item_name(def_id);
+            err.span_label(
+                arm.pattern.span,
+                format!(
+                    "this pattern doesn't introduce a new catch-all binding, but rather pattern \
+                     matches against the value of constant `{const_name}`",
+                ),
+            );
+            err.span_note(cx.tcx.def_span(def_id), format!("constant `{const_name}` defined here"));
+            err.span_suggestion_verbose(
+                arm.pattern.span.shrink_to_hi(),
+                "if you meant to introduce a binding, use a different name",
+                "_var".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
+
     // Whether we suggest the actual missing patterns or `_`.
     let suggest_the_witnesses = witnesses.len() < 4;
     let suggested_arm = if suggest_the_witnesses {

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -149,21 +149,30 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             None => Ok((None, None, None)),
             Some(expr) => {
                 let (kind, ascr, inline_const) = match self.lower_lit(expr) {
-                    PatKind::InlineConstant { subpattern, def } => {
+                    PatKind::ExpandedConstant { subpattern, def_id, is_inline: true } => {
-                        (subpattern.kind, None, Some(def))
+                        (subpattern.kind, None, def_id.as_local())
+                    }
+                    PatKind::ExpandedConstant { subpattern, is_inline: false, .. } => {
+                        (subpattern.kind, None, None)
                     }
                     PatKind::AscribeUserType { ascription, subpattern: box Pat { kind, .. } } => {
                         (kind, Some(ascription), None)
                     }
                     kind => (kind, None, None),
                 };
-                let value = if let PatKind::Constant { value } = kind {
+                let value = match kind {
+                    PatKind::Constant { value } => value,
+                    PatKind::ExpandedConstant { subpattern, .. }
+                        if let PatKind::Constant { value } = subpattern.kind =>
+                    {
                         value
-                } else {
+                    }
+                    _ => {
                         let msg = format!(
                             "found bad range pattern endpoint `{expr:?}` outside of error recovery"
                         );
                         return Err(self.tcx.dcx().span_delayed_bug(expr.span, msg));
+                    }
                 };
                 Ok((Some(PatRangeBoundary::Finite(value)), ascr, inline_const))
             }
@@ -288,7 +297,11 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             };
         }
         for def in [lo_inline, hi_inline].into_iter().flatten() {
-            kind = PatKind::InlineConstant { def, subpattern: Box::new(Pat { span, ty, kind }) };
+            kind = PatKind::ExpandedConstant {
+                def_id: def.to_def_id(),
+                is_inline: true,
+                subpattern: Box::new(Pat { span, ty, kind }),
+            };
         }
         Ok(kind)
     }
@@ -562,7 +575,12 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         let args = self.typeck_results.node_args(id);
         let c = ty::Const::new_unevaluated(self.tcx, ty::UnevaluatedConst { def: def_id, args });
-        let pattern = self.const_to_pat(c, ty, id, span);
+        let subpattern = self.const_to_pat(c, ty, id, span);
+        let pattern = Box::new(Pat {
+            span,
+            ty,
+            kind: PatKind::ExpandedConstant { subpattern, def_id, is_inline: false },
+        });
 
         if !is_associated_const {
             return pattern;
@@ -637,7 +655,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         let ct = ty::UnevaluatedConst { def: def_id.to_def_id(), args };
         let subpattern = self.const_to_pat(ty::Const::new_unevaluated(self.tcx, ct), ty, id, span);
-        PatKind::InlineConstant { subpattern, def: def_id }
+        PatKind::ExpandedConstant { subpattern, def_id: def_id.to_def_id(), is_inline: true }
     }
 
     /// Converts literals, paths and negation of literals to patterns.

compiler/rustc_mir_build/src/thir/print.rs

@@ -707,9 +707,10 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
                 print_indented!(self, format!("value: {:?}", value), depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
             }
-            PatKind::InlineConstant { def, subpattern } => {
+            PatKind::ExpandedConstant { def_id, is_inline, subpattern } => {
-                print_indented!(self, "InlineConstant {", depth_lvl + 1);
+                print_indented!(self, "ExpandedConstant {", depth_lvl + 1);
-                print_indented!(self, format!("def: {:?}", def), depth_lvl + 2);
+                print_indented!(self, format!("def_id: {def_id:?}"), depth_lvl + 2);
+                print_indented!(self, format!("is_inline: {is_inline:?}"), depth_lvl + 2);
                 print_indented!(self, "subpattern:", depth_lvl + 2);
                 self.print_pat(subpattern, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -465,7 +465,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
         let fields: Vec<_>;
         match &pat.kind {
             PatKind::AscribeUserType { subpattern, .. }
-            | PatKind::InlineConstant { subpattern, .. } => return self.lower_pat(subpattern),
+            | PatKind::ExpandedConstant { subpattern, .. } => return self.lower_pat(subpattern),
             PatKind::Binding { subpattern: Some(subpat), .. } => return self.lower_pat(subpat),
             PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
                 ctor = Wildcard;

tests/ui/closures/2229_closure_analysis/bad-pattern.stderr

@@ -97,16 +97,19 @@ LL |         if let Refutable::A = v3 { todo!() };
 error[E0005]: refutable pattern in local binding
   --> $DIR/bad-pattern.rs:19:13
    |
+LL |     const PAT: u32 = 0;
+   |     -------------- missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
+...
 LL |         let PAT = v1;
-   |             ^^^
+   |             ^^^ pattern `1_u32..=u32::MAX` not covered
-   |             |
-   |             pattern `1_u32..=u32::MAX` not covered
-   |             missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
-   |             help: introduce a variable instead: `PAT_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `u32`
+help: introduce a variable instead
+   |
+LL |         let PAT_var = v1;
+   |             ~~~~~~~
 
 error: aborting due to 7 previous errors
 

tests/ui/consts/const-pattern-irrefutable.rs

@@ -1,28 +1,43 @@
 mod foo {
     pub const b: u8 = 2;
-    pub const d: u8 = 2;
+    //~^ missing patterns are not covered because `b` is interpreted as a constant pattern, not a new variable
+    pub const d: (u8, u8) = (2, 1);
+    //~^ missing patterns are not covered because `d` is interpreted as a constant pattern, not a new variable
 }
 
 use foo::b as c;
 use foo::d;
 
 const a: u8 = 2;
+//~^ missing patterns are not covered because `a` is interpreted as a constant pattern, not a new variable
+
+#[derive(PartialEq)]
+struct S {
+    foo: u8,
+}
+
+const e: S = S {
+    foo: 0,
+};
 
 fn main() {
     let a = 4;
     //~^ ERROR refutable pattern in local binding
     //~| patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-    //~| missing patterns are not covered because `a` is interpreted as a constant pattern, not a new variable
     //~| HELP introduce a variable instead
     let c = 4;
     //~^ ERROR refutable pattern in local binding
     //~| patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-    //~| missing patterns are not covered because `c` is interpreted as a constant pattern, not a new variable
     //~| HELP introduce a variable instead
-    let d = 4;
+    let d = (4, 4);
     //~^ ERROR refutable pattern in local binding
-    //~| patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
+    //~| patterns `(0_u8..=1_u8, _)` and `(3_u8..=u8::MAX, _)` not covered
-    //~| missing patterns are not covered because `d` is interpreted as a constant pattern, not a new variable
     //~| HELP introduce a variable instead
+    let e = S {
+    //~^ ERROR refutable pattern in local binding
+    //~| pattern `S { foo: 1_u8..=u8::MAX }` not covered
+    //~| HELP introduce a variable instead
+        foo: 1,
+    };
     fn f() {} // Check that the `NOTE`s still work with an item here (cf. issue #35115).
 }

tests/ui/consts/const-pattern-irrefutable.stderr

@@ -1,45 +1,76 @@
 error[E0005]: refutable pattern in local binding
-  --> $DIR/const-pattern-irrefutable.rs:12:9
+  --> $DIR/const-pattern-irrefutable.rs:24:9
    |
+LL | const a: u8 = 2;
+   | ----------- missing patterns are not covered because `a` is interpreted as a constant pattern, not a new variable
+...
 LL |     let a = 4;
-   |         ^
+   |         ^ patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-   |         |
-   |         patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-   |         missing patterns are not covered because `a` is interpreted as a constant pattern, not a new variable
-   |         help: introduce a variable instead: `a_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `u8`
+help: introduce a variable instead
+   |
+LL |     let a_var = 4;
+   |         ~~~~~
 
 error[E0005]: refutable pattern in local binding
-  --> $DIR/const-pattern-irrefutable.rs:17:9
+  --> $DIR/const-pattern-irrefutable.rs:28:9
    |
+LL |     pub const b: u8 = 2;
+   |     --------------- missing patterns are not covered because `b` is interpreted as a constant pattern, not a new variable
+...
 LL |     let c = 4;
-   |         ^
+   |         ^ patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-   |         |
-   |         patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
-   |         missing patterns are not covered because `c` is interpreted as a constant pattern, not a new variable
-   |         help: introduce a variable instead: `c_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `u8`
+help: introduce a variable instead
+   |
+LL |     let b_var = 4;
+   |         ~~~~~
 
 error[E0005]: refutable pattern in local binding
-  --> $DIR/const-pattern-irrefutable.rs:22:9
+  --> $DIR/const-pattern-irrefutable.rs:32:9
    |
-LL |     let d = 4;
+LL |     pub const d: (u8, u8) = (2, 1);
-   |         ^
+   |     --------------------- missing patterns are not covered because `d` is interpreted as a constant pattern, not a new variable
-   |         |
+...
-   |         patterns `0_u8..=1_u8` and `3_u8..=u8::MAX` not covered
+LL |     let d = (4, 4);
-   |         missing patterns are not covered because `d` is interpreted as a constant pattern, not a new variable
+   |         ^ patterns `(0_u8..=1_u8, _)` and `(3_u8..=u8::MAX, _)` not covered
-   |         help: introduce a variable instead: `d_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
-   = note: the matched value is of type `u8`
+   = note: the matched value is of type `(u8, u8)`
+help: introduce a variable instead
+   |
+LL |     let d_var = (4, 4);
+   |         ~~~~~
 
-error: aborting due to 3 previous errors
+error[E0005]: refutable pattern in local binding
+  --> $DIR/const-pattern-irrefutable.rs:36:9
+   |
+LL | const e: S = S {
+   | ---------- missing patterns are not covered because `e` is interpreted as a constant pattern, not a new variable
+...
+LL |     let e = S {
+   |         ^ pattern `S { foo: 1_u8..=u8::MAX }` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+note: `S` defined here
+  --> $DIR/const-pattern-irrefutable.rs:15:8
+   |
+LL | struct S {
+   |        ^
+   = note: the matched value is of type `S`
+help: introduce a variable instead
+   |
+LL |     let e_var = S {
+   |         ~~~~~
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0005`.

tests/ui/consts/const_in_pattern/incomplete-slice.stderr

@@ -3,8 +3,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match &[][..] {
    |           ^^^^^^^ patterns `&[]` and `&[_, _, ..]` not covered
+LL |
+LL |         E_SL => {}
+   |         ---- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `E_SL`
    |
    = note: the matched value is of type `&[E]`
+note: constant `E_SL` defined here
+  --> $DIR/incomplete-slice.rs:6:1
+   |
+LL | const E_SL: &[E] = &[E::A];
+   | ^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         E_SL_var => {}
+   |             ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         E_SL => {},

tests/ui/match/intended-binding-pattern-is-const.rs

@@ -0,0 +1,10 @@
+fn main() {
+    match 1 { //~ ERROR non-exhaustive patterns
+        //~^ patterns `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
+        //~| the matched value is of type `i32`
+        x => {} //~ this pattern doesn't introduce a new catch-all binding
+        //~^ HELP ensure that all possible cases are being handled
+        //~| HELP if you meant to introduce a binding, use a different name
+    }
+    const x: i32 = 4; //~ NOTE constant `x` defined here
+}

tests/ui/match/intended-binding-pattern-is-const.stderr

@@ -0,0 +1,27 @@
+error[E0004]: non-exhaustive patterns: `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
+  --> $DIR/intended-binding-pattern-is-const.rs:2:11
+   |
+LL |     match 1 {
+   |           ^ patterns `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
+...
+LL |         x => {}
+   |         - this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `x`
+   |
+   = note: the matched value is of type `i32`
+note: constant `x` defined here
+  --> $DIR/intended-binding-pattern-is-const.rs:9:5
+   |
+LL |     const x: i32 = 4;
+   |     ^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         x_var => {}
+   |          ++++
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
+   |
+LL |         x => {}, i32::MIN..=3_i32 | 5_i32..=i32::MAX => todo!()
+   |                ++++++++++++++++++++++++++++++++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0004`.

tests/ui/mir/issue-112269.stderr

@@ -1,30 +1,34 @@
 error[E0005]: refutable pattern in local binding
   --> $DIR/issue-112269.rs:3:9
    |
+LL |     const x: i32 = 4;
+   |     ------------ missing patterns are not covered because `x` is interpreted as a constant pattern, not a new variable
 LL |     let x: i32 = 3;
-   |         ^
+   |         ^ patterns `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
-   |         |
-   |         patterns `i32::MIN..=3_i32` and `5_i32..=i32::MAX` not covered
-   |         missing patterns are not covered because `x` is interpreted as a constant pattern, not a new variable
-   |         help: introduce a variable instead: `x_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `i32`
+help: introduce a variable instead
+   |
+LL |     let x_var: i32 = 3;
+   |         ~~~~~
 
 error[E0005]: refutable pattern in local binding
   --> $DIR/issue-112269.rs:7:9
    |
+LL |     const y: i32 = 3;
+   |     ------------ missing patterns are not covered because `y` is interpreted as a constant pattern, not a new variable
 LL |     let y = 4;
-   |         ^
+   |         ^ patterns `i32::MIN..=2_i32` and `4_i32..=i32::MAX` not covered
-   |         |
-   |         patterns `i32::MIN..=2_i32` and `4_i32..=i32::MAX` not covered
-   |         missing patterns are not covered because `y` is interpreted as a constant pattern, not a new variable
-   |         help: introduce a variable instead: `y_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `i32`
+help: introduce a variable instead
+   |
+LL |     let y_var = 4;
+   |         ~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/pattern/usefulness/match-arm-statics-2.stderr

@@ -3,8 +3,20 @@ error[E0004]: non-exhaustive patterns: `(true, false)` not covered
    |
 LL |     match (true, false) {
    |           ^^^^^^^^^^^^^ pattern `(true, false)` not covered
+LL |
+LL |         TRUE_TRUE => (),
+   |         --------- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `TRUE_TRUE`
    |
    = note: the matched value is of type `(bool, bool)`
+note: constant `TRUE_TRUE` defined here
+  --> $DIR/match-arm-statics-2.rs:14:1
+   |
+LL | const TRUE_TRUE: (bool, bool) = (true, true);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         TRUE_TRUE_var => (),
+   |                  ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         (false, true) => (),

tests/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr

@@ -199,8 +199,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+LL |
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         CONST => {},
@@ -212,8 +224,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+LL |
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         &[false] => {},
@@ -225,8 +249,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         CONST => {},
@@ -238,8 +274,20 @@ error[E0004]: non-exhaustive patterns: `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ pattern `&[_, _, ..]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         CONST => {},
@@ -251,8 +299,20 @@ error[E0004]: non-exhaustive patterns: `&[false]` not covered
    |
 LL |     match s {
    |           ^ pattern `&[false]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         &[_, _, ..] => {},
@@ -264,8 +324,20 @@ error[E0004]: non-exhaustive patterns: `&[false]` not covered
    |
 LL |     match s1 {
    |           ^^ pattern `&[false]` not covered
+LL |
+LL |         CONST1 => {}
+   |         ------ this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST1`
    |
    = note: the matched value is of type `&[bool; 1]`
+note: constant `CONST1` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:124:5
+   |
+LL |     const CONST1: &[bool; 1] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST1_var => {}
+   |               ++++
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         CONST1 => {},

tests/ui/suggestions/const-pat-non-exaustive-let-new-var.rs

@@ -2,9 +2,9 @@ fn main() {
     let A = 3;
     //~^ ERROR refutable pattern in local binding
     //~| patterns `i32::MIN..=1_i32` and `3_i32..=i32::MAX` not covered
-    //~| missing patterns are not covered because `A` is interpreted as a constant pattern, not a new variable
     //~| HELP introduce a variable instead
     //~| SUGGESTION A_var
 
     const A: i32 = 2;
+    //~^ missing patterns are not covered because `A` is interpreted as a constant pattern, not a new variable
 }

tests/ui/suggestions/const-pat-non-exaustive-let-new-var.stderr

@@ -2,15 +2,18 @@ error[E0005]: refutable pattern in local binding
   --> $DIR/const-pat-non-exaustive-let-new-var.rs:2:9
    |
 LL |     let A = 3;
-   |         ^
+   |         ^ patterns `i32::MIN..=1_i32` and `3_i32..=i32::MAX` not covered
-   |         |
+...
-   |         patterns `i32::MIN..=1_i32` and `3_i32..=i32::MAX` not covered
+LL |     const A: i32 = 2;
-   |         missing patterns are not covered because `A` is interpreted as a constant pattern, not a new variable
+   |     ------------ missing patterns are not covered because `A` is interpreted as a constant pattern, not a new variable
-   |         help: introduce a variable instead: `A_var`
    |
    = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
    = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
    = note: the matched value is of type `i32`
+help: introduce a variable instead
+   |
+LL |     let A_var = 3;
+   |         ~~~~~
 
 error: aborting due to 1 previous error