Update grammar for order of parameters/arguments.

Generic param order restriction was changed in rust-lang/rust#58191.
Generic argument order restriction was changed in rust-lang/rust#70261.
`for` lifetime argument restriction was changed in rust-lang/rust#48326.

Generic parameter parsing: https://github.com/rust-lang/rust/blob/206ee1eea3467fd1d7f1efdbeafe27880897bb2c/compiler/rustc_parse/src/parser/generics.rs#L83-L153
Generic argument parsing: https://github.com/rust-lang/rust/blob/17eec1433c69972844dd228b5fe801f218e118c3/compiler/rustc_parse/src/parser/path.rs#L395-L413
`for` argument parsing: https://github.com/rust-lang/rust/blob/206ee1eea3467fd1d7f1efdbeafe27880897bb2c/compiler/rustc_parse/src/parser/ty.rs#L724-L736

Fixes rust-lang#785

Author: ehuss

src/items/generics.md

@@ -2,30 +2,27 @@
 
 > **<sup>Syntax</sup>**\
 > _Generics_ :\
-> &nbsp;&nbsp; `<` _GenericParams_ `>`
+> &nbsp;&nbsp; `<` _GenericParams_<sup>?</sup> `>`
 >
 > _GenericParams_ :\
-> &nbsp;&nbsp; &nbsp;&nbsp; _LifetimeParams_\
-> &nbsp;&nbsp; | ( _LifetimeParam_ `,` )<sup>\*</sup> _TypeParams_\
-> &nbsp;&nbsp; | ( _LifetimeParam_ `,` )<sup>\*</sup> ( _TypeParam_ `,` )<sup>\*</sup> _ConstParams_
+> &nbsp;&nbsp; (_GenericParam_ `,`)<sup>\*</sup> _GenericParam_ `,`<sup>?</sup>
 >
-> _LifetimeParams_ :\
-> &nbsp;&nbsp; ( _LifetimeParam_ `,` )<sup>\*</sup> _LifetimeParam_<sup>?</sup>
+> _GenericParam_ :\
+> &nbsp;&nbsp; [_OuterAttribute_] <sup>\*</sup>\
+> &nbsp;&nbsp; (\
+> &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; _LifetimeParam_\
+> &nbsp;&nbsp; &nbsp;&nbsp; | _TypeParam_\
+> &nbsp;&nbsp; &nbsp;&nbsp; | _ConstParam_\
+> &nbsp;&nbsp; )
 >
 > _LifetimeParam_ :\
-> &nbsp;&nbsp; [_OuterAttribute_]<sup>?</sup> [LIFETIME_OR_LABEL]&nbsp;( `:` [_LifetimeBounds_] )<sup>?</sup>
->
-> _TypeParams_:\
-> &nbsp;&nbsp; ( _TypeParam_ `,` )<sup>\*</sup> _TypeParam_<sup>?</sup>
+> &nbsp;&nbsp; [LIFETIME_OR_LABEL]&nbsp;( `:` [_LifetimeBounds_] )<sup>?</sup>
 >
 > _TypeParam_ :\
-> &nbsp;&nbsp; [_OuterAttribute_]<sup>?</sup> [IDENTIFIER]( `:` [_TypeParamBounds_]<sup>?</sup> )<sup>?</sup> ( `=` [_Type_] )<sup>?</sup>
->
-> _ConstParams_:\
-> &nbsp;&nbsp; ( _ConstParam_ `,` )<sup>\*</sup> _ConstParam_<sup>?</sup>
+> &nbsp;&nbsp; [IDENTIFIER]( `:` [_TypeParamBounds_]<sup>?</sup> )<sup>?</sup> ( `=` [_Type_] )<sup>?</sup>
 >
 > _ConstParam_:\
-> &nbsp;&nbsp; [_OuterAttribute_]<sup>?</sup> `const` [IDENTIFIER] `:` [_Type_]
+> &nbsp;&nbsp; `const` [IDENTIFIER] `:` [_Type_]
 
 Functions, type aliases, structs, enumerations, unions, traits, and
 implementations may be *parameterized* by types, constants, and lifetimes. These
@@ -91,12 +88,15 @@ referred to with path syntax.
 > &nbsp;&nbsp; _ForLifetimes_<sup>?</sup> [_Type_] `:` [_TypeParamBounds_]<sup>?</sup>
 >
 > _ForLifetimes_ :\
-> &nbsp;&nbsp; `for` `<` [_LifetimeParams_](#generic-parameters) `>`
+> &nbsp;&nbsp; `for` `<` [_GenericParams_](#generic-parameters) `>`
 
 *Where clauses* provide another way to specify bounds on type and lifetime
 parameters as well as a way to specify bounds on types that aren't type
 parameters.
 
+The `for` keyword can be used to introduce [higher-ranked lifetimes]. It only
+allows [_LifetimeParam_] parameters.
+
 Bounds that don't use the item's parameters or higher-ranked lifetimes are
 checked when the item is defined. It is an error for such a bound to be false.
 
@@ -141,6 +141,7 @@ struct Foo<#[my_flexible_clone(unbounded)] H> {
 [IDENTIFIER]: ../identifiers.md
 [LIFETIME_OR_LABEL]: ../tokens.md#lifetimes-and-loop-labels
 
+[_LifetimeParam_]: #generic-parameters
 [_LifetimeBounds_]: ../trait-bounds.md
 [_Lifetime_]: ../trait-bounds.md
 [_OuterAttribute_]: ../attributes.md
@@ -150,6 +151,7 @@ struct Foo<#[my_flexible_clone(unbounded)] H> {
 [arrays]: ../types/array.md
 [const contexts]: ../const_eval.md#const-context
 [function pointers]: ../types/function-pointer.md
+[higher-ranked lifetimes]: ../trait-bounds.md#higher-ranked-trait-bounds
 [raw pointers]: ../types/pointer.md#raw-pointers-const-and-mut
 [references]: ../types/pointer.md#shared-references-
 [repeat expressions]: ../expressions/array-expr.md

src/paths.md

@@ -50,37 +50,17 @@ mod m {
 >
 > _GenericArgs_ :\
 > &nbsp;&nbsp; &nbsp;&nbsp; `<` `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsTypes_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsConsts_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsBindings_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsTypes_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsConsts_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsBindings_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsTypes_ `,` _GenericArgsConsts_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsTypes_ `,` _GenericArgsBindings_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsConsts_ `,` _GenericArgsBindings_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsTypes_ `,` _GenericArgsConsts_ `,` _GenericArgsBindings_ `,`<sup>?</sup> `>`\
-> &nbsp;&nbsp; | `<` _GenericArgsLifetimes_ `,` _GenericArgsTypes_ `,` _GenericArgsConsts_ `,` _GenericArgsBindings_ `,`<sup>?</sup> `>`
+> &nbsp;&nbsp; | `<` ( _GenericArg_ `,` )<sup>\*</sup> _GenericArg_ `,`<sup>?</sup> `>`
 >
-> _GenericArgsLifetimes_ :\
-> &nbsp;&nbsp; [_Lifetime_] (`,` [_Lifetime_])<sup>\*</sup>
->
-> _GenericArgsTypes_ :\
-> &nbsp;&nbsp; [_Type_] (`,` [_Type_])<sup>\*</sup>
->
-> _GenericArgsConsts_ :\
-> &nbsp;&nbsp; _GenericArgsConst_ (`,` _GenericArgsConst_)<sup>\*</sup>
+> _GenericArg_ :\
+> &nbsp;&nbsp; [_Lifetime_] | [_Type_] | _GenericArgsConst_ | _GenericArgsBinding_
 >
 > _GenericArgsConst_ :\
 > &nbsp;&nbsp; &nbsp;&nbsp; [_BlockExpression_]\
 > &nbsp;&nbsp; | [_LiteralExpression_]\
 > &nbsp;&nbsp; | `-` [_LiteralExpression_]\
 > &nbsp;&nbsp; | [_SimplePathSegment_]
 >
-> _GenericArgsBindings_ :\
-> &nbsp;&nbsp; _GenericArgsBinding_ (`,` _GenericArgsBinding_)<sup>\*</sup>
->
 > _GenericArgsBinding_ :\
 > &nbsp;&nbsp; [IDENTIFIER] `=` [_Type_]
 
@@ -95,6 +75,9 @@ ambiguity with the less-than operator. This is colloquially known as "turbofish"
 Vec::<u8>::with_capacity(1024);
 ```
 
+The order of generic arguments is restricted to lifetime arguments, then type
+arguments, then const arguments, then equality constraints.
+
 Const arguments must be surrounded by braces unless they are a
 [literal] or a single segment path.