Rollup merge of #125015 - fmease:pat-tys-proh-gen-args-on-ct-params, r=spastorino

Pattern types: Prohibit generic args on const params

Addresses https://github.com/rust-lang/rust/pull/123689/files#r1562676629.

NB: Technically speaking, *not* prohibiting generics args on const params is not a bug as `pattern_types` is an *internal* feature and as such any uncaught misuses of it are considered to be the fault of the user. However, permitting this makes me slightly uncomfortable esp. since we might want to make pattern types available to the public at some point and I don't want this oversight to be able to slip into the language (for comparison, ICEs triggered by the use of internal features are like super fine).

Furthermore, this is an ad hoc fix. A more general fix would be changing the representation of the pattern part of pattern types in such a way that it can reuse preexisting lowering routines for exprs / anon consts. See also this [Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/pattern.20type.20HIR.20nodes/near/432410768) and #124650.

Also note that we currently don't properly typeck the pattern of pat tys. This however is out of scope for this PR.

cc ``@oli-obk``
r? ``@spastorino`` as discussed

Author: fmease

compiler/rustc_hir_analysis/messages.ftl

@@ -371,9 +371,9 @@ hir_analysis_pass_to_variadic_function = can't pass `{$ty}` to variadic function
     .suggestion = cast the value to `{$cast_ty}`
     .help = cast the value to `{$cast_ty}`
 
-hir_analysis_pattern_type_non_const_range = "range patterns must have constant range start and end"
-hir_analysis_pattern_type_wild_pat = "wildcard patterns are not permitted for pattern types"
-    .label = "this type is the same as the inner type without a pattern"
+hir_analysis_pattern_type_non_const_range = range patterns must have constant range start and end
+hir_analysis_pattern_type_wild_pat = wildcard patterns are not permitted for pattern types
+    .label = this type is the same as the inner type without a pattern
 hir_analysis_placeholder_not_allowed_item_signatures = the placeholder `_` is not allowed within types on item signatures for {$kind}
     .label = not allowed in type signatures
 

compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs

@@ -1382,7 +1382,7 @@ pub enum GenericsArgsErrExtend<'tcx> {
         span: Span,
     },
     SelfTyParam(Span),
-    TyParam(DefId),
+    Param(DefId),
     DefVariant,
     None,
 }
@@ -1498,11 +1498,11 @@ fn generics_args_err_extend<'a>(
         GenericsArgsErrExtend::DefVariant => {
             err.note("enum variants can't have type parameters");
         }
-        GenericsArgsErrExtend::TyParam(def_id) => {
-            if let Some(span) = tcx.def_ident_span(def_id) {
-                let name = tcx.item_name(def_id);
-                err.span_note(span, format!("type parameter `{name}` defined here"));
-            }
+        GenericsArgsErrExtend::Param(def_id) => {
+            let span = tcx.def_ident_span(def_id).unwrap();
+            let kind = tcx.def_descr(def_id);
+            let name = tcx.item_name(def_id);
+            err.span_note(span, format!("{kind} `{name}` defined here"));
         }
         GenericsArgsErrExtend::SelfTyParam(span) => {
             err.span_suggestion_verbose(

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -1758,7 +1758,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 assert_eq!(opt_self_ty, None);
                 let _ = self.prohibit_generic_args(
                     path.segments.iter(),
-                    GenericsArgsErrExtend::TyParam(def_id),
+                    GenericsArgsErrExtend::Param(def_id),
                 );
                 self.lower_ty_param(hir_id)
             }
@@ -2191,10 +2191,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
                                 hir::ExprKind::Path(hir::QPath::Resolved(
                                     _,
-                                    &hir::Path {
-                                        res: Res::Def(DefKind::ConstParam, def_id), ..
+                                    path @ &hir::Path {
+                                        res: Res::Def(DefKind::ConstParam, def_id),
+                                        ..
                                     },
                                 )) => {
+                                    let _ = self.prohibit_generic_args(
+                                        path.segments.iter(),
+                                        GenericsArgsErrExtend::Param(def_id),
+                                    );
                                     let ty = tcx
                                         .type_of(def_id)
                                         .no_bound_vars()

tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.rs

@@ -0,0 +1,10 @@
+#![feature(pattern_types, core_pattern_type)]
+#![allow(internal_features)]
+
+type Pat<const START: u32, const END: u32> =
+    std::pat::pattern_type!(u32 is START::<(), i32, 2>..=END::<_, Assoc = ()>);
+//~^ ERROR type and const arguments are not allowed on const parameter `START`
+//~| ERROR type arguments are not allowed on const parameter `END`
+//~| ERROR associated type bindings are not allowed here
+
+fn main() {}

tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.stderr

@@ -0,0 +1,38 @@
+error[E0109]: type and const arguments are not allowed on const parameter `START`
+  --> $DIR/bad_const_generics_args_on_const_param.rs:5:44
+   |
+LL |     std::pat::pattern_type!(u32 is START::<(), i32, 2>..=END::<_, Assoc = ()>);
+   |                                    -----   ^^  ^^^  ^ type and const arguments not allowed
+   |                                    |
+   |                                    not allowed on const parameter `START`
+   |
+note: const parameter `START` defined here
+  --> $DIR/bad_const_generics_args_on_const_param.rs:4:16
+   |
+LL | type Pat<const START: u32, const END: u32> =
+   |                ^^^^^
+
+error[E0109]: type arguments are not allowed on const parameter `END`
+  --> $DIR/bad_const_generics_args_on_const_param.rs:5:64
+   |
+LL |     std::pat::pattern_type!(u32 is START::<(), i32, 2>..=END::<_, Assoc = ()>);
+   |                                                          ---   ^ type argument not allowed
+   |                                                          |
+   |                                                          not allowed on const parameter `END`
+   |
+note: const parameter `END` defined here
+  --> $DIR/bad_const_generics_args_on_const_param.rs:4:34
+   |
+LL | type Pat<const START: u32, const END: u32> =
+   |                                  ^^^
+
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/bad_const_generics_args_on_const_param.rs:5:67
+   |
+LL |     std::pat::pattern_type!(u32 is START::<(), i32, 2>..=END::<_, Assoc = ()>);
+   |                                                                   ^^^^^^^^^^ associated type not allowed here
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0109, E0229.
+For more information about an error, try `rustc --explain E0109`.

tests/ui/type/pattern_types/bad_pat.stderr

@@ -14,7 +14,7 @@ LL | type Positive2 = pattern_type!(i32 is 0..=);
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
-error: "wildcard patterns are not permitted for pattern types"
+error: wildcard patterns are not permitted for pattern types
   --> $DIR/bad_pat.rs:11:33
    |
 LL | type Wild = pattern_type!(() is _);