Remove InferredConst production

In actuality, the parser is going to treat an inferred const as an
inferred type, so we don't need a separate rule for this, and removing
this rule avoids some ambiguity in our grammar.  We'll add a note
describing this situation.

Author: traviscross

src/items/generics.md

@@ -172,12 +172,12 @@ fn example() {
 ```
 
 r[items.generics.const.inferred]
-Where a const argument is expected, an `_` (optionally surrounding by any number of matching parentheses), called the *inferred const* ([grammar][InferredConst], [path rules][paths.expr.complex-const-params]), can be used instead. This asks the compiler to infer the const argument if possible based on surrounding information.
+Where a const argument is expected, an `_` (optionally surrounding by any number of matching parentheses), called the *inferred const* ([path rules][paths.expr.complex-const-params]), can be used instead. This asks the compiler to infer the const argument if possible based on surrounding information.
 
 ```rust
 fn make_buf<const N: usize>() -> [u8; N] {
-    [0x1; _]
-    //    ^ Infers `N`.
+    [0; _]
+    //  ^ Infers `N`.
 }
 let _: [u8; 1024] = make_buf::<_>();
 //                             ^ Infers `1024`.

src/paths.md

@@ -62,15 +62,10 @@ GenericArg ->
 
 GenericArgsConst ->
       BlockExpression
-    | InferredConst
     | LiteralExpression
     | `-` LiteralExpression
     | SimplePathSegment
 
-InferredConst ->
-    | `(` InferredConst `)`
-    | `_`
-
 GenericArgsBinding ->
     IDENTIFIER GenericArgs? `=` Type
 
@@ -96,7 +91,7 @@ The order of generic arguments is restricted to lifetime arguments, then type
 arguments, then const arguments, then equality constraints.
 
 r[paths.expr.complex-const-params]
-Const arguments must be surrounded by braces unless they are a [literal], an [inferred const] ([grammar][InferredConst]), or a single segment path.
+Const arguments must be surrounded by braces unless they are a [literal], an [inferred const], or a single segment path.
 
 ```rust
 mod m {
@@ -112,6 +107,9 @@ let _ = f::<C>(); // Single segment path.
 let _ = f::<{ m::C }>(); // Multi-segment path must be braced.
 ```
 
+> [!NOTE]
+> An [inferred const] is parsed as an [inferred type] but then semantically treated as a separate kind of [const generic argument].
+
 r[paths.expr.impl-trait-params]
 The synthetic type parameters corresponding to `impl Trait` types are implicit,
 and these cannot be explicitly specified.
@@ -498,11 +496,13 @@ mod without { // crate::without
 [`Self` scope]: names/scopes.md#self-scope
 [`use`]: items/use-declarations.md
 [attributes]: attributes.md
+[const generic argument]: items.generics.const.argument
 [enumeration]: items/enumerations.md
 [expressions]: expressions.md
 [extern prelude]: names/preludes.md#extern-prelude
 [implementation]: items/implementations.md
 [inferred const]: items.generics.const.inferred
+[inferred type]: type.inferred
 [macro transcribers]: macros-by-example.md
 [macros]: macros.md
 [mbe]: macros-by-example.md