Document inferred const args (feature(generic_arg_infer))

src/items/generics.md

@@ -227,6 +227,28 @@ fn generic<const B: bool>() {
 }
 ```
 
+r[items.generics.const.inferred]
+
+r[items.generics.const.inferred.syntax]
+```grammar,items
+InferredConst ->
+      `_`
+    | `(` InferredConst `)`
+```
+
+r[items.generics.const.inferred.intro]
+Where a const argument is expected, an `_` (optionally surrounding by any number of matching parentheses), called the "inferred const", can be used instead. This asks the compiler to infer the const argument if possible based on surrounding information.
+
+```rust
+fn make_buf() -> [u8; 1024] {
+    [0x1; _]
+    //    ^ Infers `1024`.
+}
+```
+
+r[items.generics.const.inferred.constraint]
+It cannot be used in item signatures.
+
 r[items.generics.where]
 ## Where clauses
 

src/paths.md

@@ -65,6 +65,7 @@ GenericArgsConst ->
     | LiteralExpression
     | `-` LiteralExpression
     | SimplePathSegment
+    | InferredConst
 
 GenericArgsBinding ->
     IDENTIFIER GenericArgs? `=` Type