Enforce a whitelist on the constant primitive types allowed in patterns.

src/librustc_mir_build/hair/pattern/const_to_pat.rs

@@ -101,20 +101,24 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                 cv.ty, structural
             );
             if let Some(non_sm_ty) = structural {
-                let adt_def = match non_sm_ty {
-                    traits::NonStructuralMatchTy::Adt(adt_def) => adt_def,
+                let msg = match non_sm_ty {
+                    traits::NonStructuralMatchTy::Adt(adt_def) => {
+                        let path = self.tcx().def_path_str(adt_def.did);
+                        format!(
+                            "to use a constant of type `{}` in a pattern, \
+                             `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
+                            path, path,
+                        )
+                    }
                     traits::NonStructuralMatchTy::Param => {
                         bug!("use of constant whose type is a parameter inside a pattern")
                     }
-                };
-                let path = self.tcx().def_path_str(adt_def.did);
-
-                let make_msg = || -> String {
-                    format!(
-                        "to use a constant of type `{}` in a pattern, \
-                         `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
-                        path, path,
-                    )
+                    traits::NonStructuralMatchTy::FnPtr => {
+                        format!("`fn` pointers cannot be used in a patterns")
+                    }
+                    traits::NonStructuralMatchTy::RawPtr => {
+                        format!("raw pointers cannot be used in a patterns")
+                    }
                 };
 
                 // double-check there even *is* a semantic `PartialEq` to dispatch to.
@@ -145,13 +149,13 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
 
                 if !ty_is_partial_eq {
                     // span_fatal avoids ICE from resolution of non-existent method (rare case).
-                    self.tcx().sess.span_fatal(self.span, &make_msg());
+                    self.tcx().sess.span_fatal(self.span, &msg);
                 } else {
                     self.tcx().struct_span_lint_hir(
                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
                         self.id,
                         self.span,
-                        |lint| lint.build(&make_msg()).emit(),
+                        |lint| lint.build(&msg).emit(),
                     );
                 }
             }
@@ -257,7 +261,39 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                 slice: None,
                 suffix: Vec::new(),
             },
-            _ => PatKind::Constant { value: cv },
+            _ => {
+                let mut leaf_ty = cv.ty;
+
+                // HACK(eddyb) workaround missing reference destructuring.
+                loop {
+                    leaf_ty = match leaf_ty.kind {
+                        ty::Ref(_, pointee_ty, _) => pointee_ty,
+
+                        // HACK(eddyb) even worse, these show up *behind*
+                        // references, so despite being supported above we have
+                        // to reimplement them here (and we can't really do the
+                        // same for nested tuples or ADTs...).
+                        ty::Array(elem_ty, _) | ty::Slice(elem_ty) => elem_ty,
+
+                        _ => break,
+                    };
+                }
+
+                match leaf_ty.kind {
+                    ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Str | ty::FnDef(..) => {
+                        PatKind::Constant { value: cv }
+                    }
+
+                    _ => {
+                        debug!("non-structural leaf constant type {:?}", leaf_ty);
+                        let msg =
+                            format!("constants of type `{}` cannot be used in a pattern", leaf_ty);
+                        self.saw_const_match_error.set(true);
+                        tcx.sess.span_err(span, &msg);
+                        PatKind::Wild
+                    }
+                }
+            }
         };
 
         Pat { span, ty: cv.ty, kind: Box::new(kind) }

src/librustc_trait_selection/traits/structural_match.rs

@@ -11,6 +11,8 @@ use rustc_span::Span;
 pub enum NonStructuralMatchTy<'tcx> {
     Adt(&'tcx AdtDef),
     Param,
+    FnPtr,
+    RawPtr,
 }
 
 /// This method traverses the structure of `ty`, trying to find an
@@ -138,26 +140,16 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
                 return true; // Stop visiting.
             }
             ty::RawPtr(..) => {
-                // structural-match ignores substructure of
-                // `*const _`/`*mut _`, so skip `super_visit_with`.
-                //
-                // For example, if you have:
-                // ```
-                // struct NonStructural;
-                // #[derive(PartialEq, Eq)]
-                // struct T(*const NonStructural);
-                // const C: T = T(std::ptr::null());
-                // ```
-                //
-                // Even though `NonStructural` does not implement `PartialEq`,
-                // structural equality on `T` does not recur into the raw
-                // pointer. Therefore, one can still use `C` in a pattern.
-
-                // (But still tell caller to continue search.)
-                return false;
+                self.found = Some(NonStructuralMatchTy::RawPtr);
+                return true; // Stop visiting.
+            }
+            ty::FnPtr(..) => {
+                self.found = Some(NonStructuralMatchTy::FnPtr);
+                return true; // Stop visiting.
             }
-            ty::FnDef(..) | ty::FnPtr(..) => {
-                // types of formals and return in `fn(_) -> _` are also irrelevant;
+            ty::FnDef(..) => {
+                // substs of ZST function (*not* `fn(...) -> _` pointers!) types
+                // are also irrelevant;
                 // so we do not recur into them via `super_visit_with`
                 //
                 // (But still tell caller to continue search.)

src/test/ui/const-generics/fn-const-param-infer.stderr

@@ -6,44 +6,12 @@ LL | #![feature(const_generics, const_compare_raw_pointers)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
-error[E0308]: mismatched types
-  --> $DIR/fn-const-param-infer.rs:16:31
+error[E0741]: the types of const generic parameters must derive `PartialEq` and `Eq`
+  --> $DIR/fn-const-param-infer.rs:4:25
    |
-LL |     let _: Checked<not_one> = Checked::<not_two>;
-   |            ----------------   ^^^^^^^^^^^^^^^^^^ expected `{not_one as fn(usize) -> bool}`, found `{not_two as fn(usize) -> bool}`
-   |            |
-   |            expected due to this
-   |
-   = note: expected struct `Checked<{not_one as fn(usize) -> bool}>`
-              found struct `Checked<{not_two as fn(usize) -> bool}>`
-
-error[E0308]: mismatched types
-  --> $DIR/fn-const-param-infer.rs:20:24
-   |
-LL |     let _ = Checked::<{generic_arg::<u32>}>;
-   |                        ^^^^^^^^^^^^^^^^^^ expected `usize`, found `u32`
-   |
-   = note: expected fn pointer `fn(usize) -> _`
-                 found fn item `fn(u32) -> _ {generic_arg::<u32>}`
-
-error[E0282]: type annotations needed
-  --> $DIR/fn-const-param-infer.rs:22:23
-   |
-LL |     let _ = Checked::<generic>;
-   |                       ^^^^^^^ cannot infer type for type parameter `T` declared on the function `generic`
-
-error[E0308]: mismatched types
-  --> $DIR/fn-const-param-infer.rs:25:40
-   |
-LL |     let _: Checked<{generic::<u32>}> = Checked::<{generic::<u16>}>;
-   |            -------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{generic::<u32> as fn(usize) -> bool}`, found `{generic::<u16> as fn(usize) -> bool}`
-   |            |
-   |            expected due to this
-   |
-   = note: expected struct `Checked<{generic::<u32> as fn(usize) -> bool}>`
-              found struct `Checked<{generic::<u16> as fn(usize) -> bool}>`
+LL | struct Checked<const F: fn(usize) -> bool>;
+   |                         ^^^^^^^^^^^^^^^^^ `fn(usize) -> bool` doesn't derive both `PartialEq` and `Eq`
 
-error: aborting due to 4 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0282, E0308.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0741`.

src/test/ui/const-generics/raw-ptr-const-param.stderr

@@ -6,17 +6,12 @@ LL | #![feature(const_generics, const_compare_raw_pointers)]
    |
    = note: `#[warn(incomplete_features)]` on by default
 
-error[E0308]: mismatched types
-  --> $DIR/raw-ptr-const-param.rs:7:40
+error[E0741]: the types of const generic parameters must derive `PartialEq` and `Eq`
+  --> $DIR/raw-ptr-const-param.rs:4:23
    |
-LL |     let _: Const<{ 15 as *const _ }> = Const::<{ 10 as *const _ }>;
-   |            -------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{0xf as *const u32}`, found `{0xa as *const u32}`
-   |            |
-   |            expected due to this
-   |
-   = note: expected struct `Const<{0xf as *const u32}>`
-              found struct `Const<{0xa as *const u32}>`
+LL | struct Const<const P: *const u32>;
+   |                       ^^^^^^^^^^ `*const u32` doesn't derive both `PartialEq` and `Eq`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0741`.

src/test/ui/consts/match_ice.stderr

@@ -4,24 +4,23 @@ error: to use a constant of type `S` in a pattern, `S` must be annotated with `#
 LL |         C => {}
    |         ^
 
-error[E0004]: non-exhaustive patterns: `&T` not covered
-  --> $DIR/match_ice.rs:16:11
+error: constants of type `T` cannot be used in a pattern
+  --> $DIR/match_ice.rs:17:9
    |
-LL | struct T;
-   | --------- `T` defined here
-...
-LL |     match K {
-   |           ^ pattern `&T` not covered
-   |
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
-   = note: the matched value is of type `&T`
+LL |         K => {}
+   |         ^
 
 error: to use a constant of type `S` in a pattern, `S` must be annotated with `#[derive(PartialEq, Eq)]`
   --> $DIR/match_ice.rs:11:9
    |
 LL |         C => {}
    |         ^
 
-error: aborting due to 3 previous errors
+error: constants of type `T` cannot be used in a pattern
+  --> $DIR/match_ice.rs:17:9
+   |
+LL |         K => {}
+   |         ^
+
+error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0004`.

src/test/ui/feature-gates/feature-gate-const_generics-ptr.stderr

@@ -25,6 +25,12 @@ LL | struct ConstFn<const F: fn()>;
    = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
    = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
 
+error[E0741]: the types of const generic parameters must derive `PartialEq` and `Eq`
+  --> $DIR/feature-gate-const_generics-ptr.rs:1:25
+   |
+LL | struct ConstFn<const F: fn()>;
+   |                         ^^^^ `fn()` doesn't derive both `PartialEq` and `Eq`
+
 error[E0658]: using raw pointers as const generic parameters is unstable
   --> $DIR/feature-gate-const_generics-ptr.rs:5:26
    |
@@ -34,6 +40,13 @@ LL | struct ConstPtr<const P: *const u32>;
    = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
    = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
 
-error: aborting due to 4 previous errors
+error[E0741]: the types of const generic parameters must derive `PartialEq` and `Eq`
+  --> $DIR/feature-gate-const_generics-ptr.rs:5:26
+   |
+LL | struct ConstPtr<const P: *const u32>;
+   |                          ^^^^^^^^^^ `*const u32` doesn't derive both `PartialEq` and `Eq`
+
+error: aborting due to 6 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors have detailed explanations: E0658, E0741.
+For more information about an error, try `rustc --explain E0658`.

src/test/ui/rfc1445/issue-61188-match-slice-forbidden-without-eq.stderr

@@ -1,8 +1,14 @@
-error: to use a constant of type `B` in a pattern, `B` must be annotated with `#[derive(PartialEq, Eq)]`
+error: constants of type `B` cannot be used in a pattern
   --> $DIR/issue-61188-match-slice-forbidden-without-eq.rs:15:9
    |
 LL |         A => (),
    |         ^
 
-error: aborting due to previous error
+error: constants of type `B` cannot be used in a pattern
+  --> $DIR/issue-61188-match-slice-forbidden-without-eq.rs:15:9
+   |
+LL |         A => (),
+   |         ^
+
+error: aborting due to 2 previous errors