Auto merge of #116236 - dtolnay:builtinmacrocomment, r=cjgillot

Modernize rustc_builtin_macros generics helpers

- Rustfmt-compatible formatting for the code snippets in comments
- Eliminate an _"Extra scope required"_ obsoleted by NLL

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -37,8 +37,9 @@
 //! following snippet
 //!
 //! ```rust
-//! # #![allow(dead_code)]
-//! struct A { x : i32 }
+//! struct A {
+//!     x: i32,
+//! }
 //!
 //! struct B(i32);
 //!
@@ -74,6 +75,7 @@
 //! trait PartialEq {
 //!     fn eq(&self, other: &Self) -> bool;
 //! }
+//!
 //! impl PartialEq for i32 {
 //!     fn eq(&self, other: &i32) -> bool {
 //!         *self == *other
@@ -90,10 +92,10 @@
 //!
 //! ```text
 //! Struct(vec![FieldInfo {
-//!            span: <span of x>
+//!     span: <span of x>,
 //!     name: Some(<ident of x>),
 //!     self_: <expr for &self.x>,
-//!            other: vec![<expr for &other.x]
+//!     other: vec![<expr for &other.x>],
 //! }])
 //! ```
 //!
@@ -101,10 +103,10 @@
 //!
 //! ```text
 //! Struct(vec![FieldInfo {
-//!           span: <span of `i32`>,
+//!     span: <span of i32>,
 //!     name: None,
-//!           self_: <expr for &a>
-//!           other: vec![<expr for &b>]
+//!     self_: <expr for &a>,
+//!     other: vec![<expr for &b>],
 //! }])
 //! ```
 //!
@@ -114,33 +116,42 @@
 //! == C0(b)`, the SubstructureFields is
 //!
 //! ```text
-//! EnumMatching(0, <ast::Variant for C0>,
+//! EnumMatching(
+//!     0,
+//!     <ast::Variant for C0>,
 //!     vec![FieldInfo {
-//!                 span: <span of i32>
+//!         span: <span of i32>,
 //!         name: None,
 //!         self_: <expr for &a>,
-//!                 other: vec![<expr for &b>]
-//!               }])
+//!         other: vec![<expr for &b>],
+//!     }],
+//! )
 //! ```
 //!
 //! For `C1 {x}` and `C1 {x}`,
 //!
 //! ```text
-//! EnumMatching(1, <ast::Variant for C1>,
+//! EnumMatching(
+//!     1,
+//!     <ast::Variant for C1>,
 //!     vec![FieldInfo {
-//!                 span: <span of x>
+//!         span: <span of x>,
 //!         name: Some(<ident of x>),
 //!         self_: <expr for &self.x>,
-//!                 other: vec![<expr for &other.x>]
-//!                }])
+//!         other: vec![<expr for &other.x>],
+//!     }],
+//! )
 //! ```
 //!
 //! For the tags,
 //!
 //! ```text
 //! EnumTag(
-//!     &[<ident of self tag>, <ident of other tag>], <expr to combine with>)
+//!     &[<ident of self tag>, <ident of other tag>],
+//!     <expr to combine with>,
+//! )
 //! ```
+//!
 //! Note that this setup doesn't allow for the brute-force "match every variant
 //! against every other variant" approach, which is bad because it produces a
 //! quadratic amount of code (see #15375).
@@ -154,9 +165,13 @@
 //!
 //! StaticStruct(<ast::VariantData of B>, Unnamed(vec![<span of x>]))
 //!
-//! StaticEnum(<ast::EnumDef of C>,
-//!            vec![(<ident of C0>, <span of C0>, Unnamed(vec![<span of i32>])),
-//!                 (<ident of C1>, <span of C1>, Named(vec![(<ident of x>, <span of x>)]))])
+//! StaticEnum(
+//!     <ast::EnumDef of C>,
+//!     vec![
+//!         (<ident of C0>, <span of C0>, Unnamed(vec![<span of i32>])),
+//!         (<ident of C1>, <span of C1>, Named(vec![(<ident of x>, <span of x>)])),
+//!     ],
+//! )
 //! ```
 
 pub use StaticFields::*;
@@ -522,7 +537,10 @@ impl<'a> TraitDef<'a> {
     /// Given that we are deriving a trait `DerivedTrait` for a type like:
     ///
     /// ```ignore (only-for-syntax-highlight)
-    /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z> where C: WhereTrait {
+    /// struct Struct<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z>
+    /// where
+    ///     C: WhereTrait,
+    /// {
     ///     a: A,
     ///     b: B::Item,
     ///     b1: <B as DeclaredTrait>::Item,
@@ -535,7 +553,8 @@ impl<'a> TraitDef<'a> {
     /// create an impl like:
     ///
     /// ```ignore (only-for-syntax-highlight)
-    /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ... Z> where
+    /// impl<'a, ..., 'z, A, B: DeclaredTrait, C, ..., Z>
+    /// where
     ///     C: WhereTrait,
     ///     A: DerivedTrait + B1 + ... + BN,
     ///     B: DerivedTrait + B1 + ... + BN,
@@ -676,18 +695,13 @@ impl<'a> TraitDef<'a> {
             }
         }));
 
-        {
-            // Extra scope required here so ty_params goes out of scope before params is moved
-
-            let mut ty_params = params
+        let ty_param_names: Vec<Symbol> = params
             .iter()
             .filter(|param| matches!(param.kind, ast::GenericParamKind::Type { .. }))
-                .peekable();
-
-            if ty_params.peek().is_some() {
-                let ty_param_names: Vec<Symbol> =
-                    ty_params.map(|ty_param| ty_param.ident.name).collect();
+            .map(|ty_param| ty_param.ident.name)
+            .collect();
 
+        if !ty_param_names.is_empty() {
             for field_ty in field_tys {
                 let field_ty_params = find_type_parameters(&field_ty, &ty_param_names, cx);
 
@@ -738,7 +752,6 @@ impl<'a> TraitDef<'a> {
                 }
             }
         }
-        }
 
         let trait_generics = Generics { params, where_clause, span };
 
@@ -1026,6 +1039,7 @@ impl<'a> MethodDef<'a> {
     }
 
     /// The normal case uses field access.
+    ///
     /// ```
     /// #[derive(PartialEq)]
     /// # struct Dummy;
@@ -1038,10 +1052,12 @@ impl<'a> MethodDef<'a> {
     ///     }
     /// }
     /// ```
+    ///
     /// But if the struct is `repr(packed)`, we can't use something like
     /// `&self.x` because that might cause an unaligned ref. So for any trait
     /// method that takes a reference, we use a local block to force a copy.
     /// This requires that the field impl `Copy`.
+    ///
     /// ```rust,ignore (example)
     /// # struct A { x: u8, y: u8 }
     /// impl PartialEq for A {
@@ -1053,7 +1069,7 @@ impl<'a> MethodDef<'a> {
     /// impl Hash for A {
     ///     fn hash<__H: ::core::hash::Hasher>(&self, state: &mut __H) -> () {
     ///         ::core::hash::Hash::hash(&{ self.x }, state);
-    ///         ::core::hash::Hash::hash(&{ self.y }, state)
+    ///         ::core::hash::Hash::hash(&{ self.y }, state);
     ///     }
     /// }
     /// ```
@@ -1107,7 +1123,9 @@ impl<'a> MethodDef<'a> {
     ///     A2(i32)
     /// }
     /// ```
+    ///
     /// is equivalent to:
+    ///
     /// ```
     /// #![feature(core_intrinsics)]
     /// enum A {
@@ -1119,15 +1137,15 @@ impl<'a> MethodDef<'a> {
     ///     fn eq(&self, other: &A) -> bool {
     ///         let __self_tag = ::core::intrinsics::discriminant_value(self);
     ///         let __arg1_tag = ::core::intrinsics::discriminant_value(other);
-    ///         __self_tag == __arg1_tag &&
-    ///             match (self, other) {
-    ///                 (A::A2(__self_0), A::A2(__arg1_0)) =>
-    ///                     *__self_0 == *__arg1_0,
+    ///         __self_tag == __arg1_tag
+    ///             && match (self, other) {
+    ///                 (A::A2(__self_0), A::A2(__arg1_0)) => *__self_0 == *__arg1_0,
     ///                 _ => true,
     ///             }
     ///     }
     /// }
     /// ```
+    ///
     /// Creates a tag check combined with a match for a tuple of all
     /// `selflike_args`, with an arm for each variant with fields, possibly an
     /// arm for each fieldless variant (if `unify_fieldless_variants` is not
@@ -1349,7 +1367,7 @@ impl<'a> MethodDef<'a> {
         //          (Variant1, Variant1, ...) => Body1
         //          (Variant2, Variant2, ...) => Body2,
         //          ...
-        //          _ => ::core::intrinsics::unreachable()
+        //          _ => ::core::intrinsics::unreachable(),
         //      }
         let get_match_expr = |mut selflike_args: ThinVec<P<Expr>>| {
             let match_arg = if selflike_args.len() == 1 {