Auto merge of #74877 - lcnr:min_const_generics, r=oli-obk

Implement the `min_const_generics` feature gate

Implements both https://github.com/rust-lang/lang-team/issues/37 and https://github.com/rust-lang/compiler-team/issues/332.

Adds the new feature gate `#![feature(min_const_generics)]`.
This feature gate adds the following limitations to using const generics:
- generic parameters must only be used in types if they are trivial. (either `N` or `{ N }`)
- generic parameters must be either integers, `bool` or `char`.

We do allow arbitrary expressions in associated consts though, meaning that the following is allowed,
even if `<[u8; 0] as Foo>::ASSOC` is not const evaluatable.
```rust
trait Foo {
    const ASSOC: usize;
}

impl<const N: usize> Foo for [u8; N] {
    const ASSOC: usize = 64 / N;
}
```

r? @varkor cc @eddyb @withoutboats

1 files changed, 1 insertions, 1 deletions

diff --git a/src/librustc_parse/parser/generics.rs b/src/librustc_parse/parser/generics.rs
index 47794746126..be72ed6dffb 100644
--- a/src/librustc_parse/parser/generics.rs
+++ b/src/librustc_parse/parser/generics.rs
@@ -54,7 +54,7 @@ impl<'a> Parser<'a> {
         self.expect(&token::Colon)?;
         let ty = self.parse_ty()?;
 
-        self.sess.gated_spans.gate(sym::const_generics, const_span.to(self.prev_token.span));
+        self.sess.gated_spans.gate(sym::min_const_generics, const_span.to(self.prev_token.span));
 
         Ok(GenericParam {
             ident,