Update extern block grammar to be before validation.

The grammar in the reference defines the grammar before ast validation,
since that is the grammar accepted by macros. Any restrictions imposed
by validation are described in prose (using the term "semantically",
but I don't feel like that is the greatest term to use).

Author: ehuss

src/items/external-blocks.md

@@ -10,12 +10,10 @@
 > _ExternalItem_ :\
 > &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> (\
 > &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; [_MacroInvocationSemi_]\
-> &nbsp;&nbsp; &nbsp;&nbsp; | ( [_Visibility_]<sup>?</sup> ( (`safe` | `unsafe`)<sup>?</sup>[^static-qualifiers] [_StaticItem_] | [_Function_] ) )\
+> &nbsp;&nbsp; &nbsp;&nbsp; | ( [_Visibility_]<sup>?</sup> ( [_StaticItem_] | [_Function_] ) )\
 > &nbsp;&nbsp; )
 >
 > [^unsafe-2024]: Starting with the 2024 Edition, the `unsafe` keyword is required semantically.
->
-> [^static-qualifiers]: *Relevant to editions earlier than Rust 2024*: The `safe` or `unsafe` qualifier is only allowed when the `extern` is qualified as `unsafe`.
 
 External blocks provide _declarations_ of items that are not _defined_ in the
 current crate and are the basis of Rust's foreign function interface. These are

src/items/functions.md

@@ -8,7 +8,10 @@
 >       ( [_BlockExpression_] | `;` )
 >
 > _FunctionQualifiers_ :\
-> &nbsp;&nbsp; `const`<sup>?</sup> `async`[^async-edition]<sup>?</sup> (`safe`[^extern-safe] | `unsafe`)<sup>?</sup>[^extern-qualifiers] (`extern` _Abi_<sup>?</sup>)<sup>?</sup>
+> &nbsp;&nbsp; `const`<sup>?</sup> `async`[^async-edition]<sup>?</sup> _ItemSafety_<sup>?</sup>[^extern-qualifiers] (`extern` _Abi_<sup>?</sup>)<sup>?</sup>
+>
+> _ItemSafety_ :\
+> &nbsp;&nbsp; `safe`[^extern-safe] | `unsafe`
 >
 > _Abi_ :\
 > &nbsp;&nbsp; [STRING_LITERAL] | [RAW_STRING_LITERAL]
@@ -39,7 +42,7 @@
 >
 > [^async-edition]: The `async` qualifier is not allowed in the 2015 edition.
 >
-> [^extern-safe]: The `safe` function qualifier is only allowed within
+> [^extern-safe]: The `safe` function qualifier is only allowed semantically within
 >   `extern` blocks.
 >
 > [^extern-qualifiers]: *Relevant to editions earlier than Rust 2024*: Within
@@ -65,6 +68,8 @@ fn answer_to_life_the_universe_and_everything() -> i32 {
 }
 ```
 
+The `safe` function is semantically only allowed when used in an [`extern` block].
+
 ## Function parameters
 
 Function parameters are irrefutable [patterns], so any pattern that is valid in
@@ -424,3 +429,4 @@ fn foo_oof(#[some_inert_attribute] arg: u8) {
 [implementation]: implementations.md
 [value namespace]: ../names/namespaces.md
 [variadic function]: external-blocks.md#variadic-functions
+[`extern` block]: external-blocks.md

src/items/static-items.md

@@ -2,8 +2,11 @@
 
 > **<sup>Syntax</sup>**\
 > _StaticItem_ :\
-> &nbsp;&nbsp; `static` `mut`<sup>?</sup> [IDENTIFIER] `:` [_Type_]
+> &nbsp;&nbsp; [_ItemSafety_]<sup>?</sup>[^extern-safety] `static` `mut`<sup>?</sup> [IDENTIFIER] `:` [_Type_]
 >              ( `=` [_Expression_] )<sup>?</sup> `;`
+>
+> [^extern-safety]: The `safe` and `unsafe` function qualifiers are only
+>   allowed semantically within `extern` blocks.
 
 A *static item* is similar to a [constant], except that it represents a precise
 memory location in the program. All references to the static refer to the same
@@ -28,6 +31,8 @@ statics:
 The initializer expression must be omitted in an [external block], and must be
 provided for free static items.
 
+The `safe` and `unsafe` qualifiers are semantically only allowed when used in an [external block].
+
 ## Statics & generics
 
 A static item defined in a generic scope (for example in a blanket or default
@@ -139,3 +144,4 @@ following are true:
 [_Type_]: ../types.md#type-expressions
 [_Expression_]: ../expressions.md
 [value namespace]: ../names/namespaces.md
+[_ItemSafety_]: functions.md