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

3 files changed, 49 insertions, 1 deletions

diff --git a/tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.rs b/tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.rs
new file mode 100644
index 00000000000..050b7b44b4e
--- /dev/null
+++ b/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() {}
diff --git a/tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.stderr b/tests/ui/type/pattern_types/bad_const_generics_args_on_const_param.stderr
new file mode 100644
index 00000000000..40effe924da
--- /dev/null
+++ b/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`.
diff --git a/tests/ui/type/pattern_types/bad_pat.stderr b/tests/ui/type/pattern_types/bad_pat.stderr
index 4f0f0bc9742..2abf27100c1 100644
--- a/tests/ui/type/pattern_types/bad_pat.stderr
+++ b/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 _);