Move ast::Item::ident into ast::ItemKind.

`ast::Item` has an `ident` field.

- It's always non-empty for these item kinds: `ExternCrate`, `Static`,
  `Const`, `Fn`, `Mod`, `TyAlias`, `Enum`, `Struct`, `Union`,
  `Trait`, `TraitAlias`, `MacroDef`, `Delegation`.

- It's always empty for these item kinds: `Use`, `ForeignMod`,
  `GlobalAsm`, `Impl`, `MacCall`, `DelegationMac`.

There is a similar story for `AssocItemKind` and `ForeignItemKind`.

Some sites that handle items check for an empty ident, some don't. This
is a very C-like way of doing things, but this is Rust, we have sum
types, we can do this properly and never forget to check for the
exceptional case and never YOLO possibly empty identifiers (or possibly
dummy spans) around and hope that things will work out.

The commit is large but it's mostly obvious plumbing work. Some notable
things.

- `ast::Item` got 8 bytes bigger. This could be avoided by boxing the
  fields within some of the `ast::ItemKind` variants (specifically:
  `Struct`, `Union`, `Enum`). I might do that in a follow-up; this
  commit is big enough already.

- For the visitors: `FnKind` no longer needs an `ident` field because
  the `Fn` within how has one.

- In the parser, the `ItemInfo` typedef is no longer needed. It was used
  in various places to return an `Ident` alongside an `ItemKind`, but
  now the `Ident` (if present) is within the `ItemKind`.

- In a few places I renamed identifier variables called `name` (or
  `foo_name`) as `ident` (or `foo_ident`), to better match the type, and
  because `name` is normally used for `Symbol`s. It's confusing to see
  something like `foo_name.name`.

clippy_utils/src/ast_utils/mod.rs

@@ -321,17 +321,18 @@ pub fn eq_local_kind(l: &LocalKind, r: &LocalKind) -> bool {
 }
 
 pub fn eq_item<K>(l: &Item<K>, r: &Item<K>, mut eq_kind: impl FnMut(&K, &K) -> bool) -> bool {
-    eq_id(l.ident, r.ident) && over(&l.attrs, &r.attrs, eq_attr) && eq_vis(&l.vis, &r.vis) && eq_kind(&l.kind, &r.kind)
+    over(&l.attrs, &r.attrs, eq_attr) && eq_vis(&l.vis, &r.vis) && eq_kind(&l.kind, &r.kind)
 }
 
 #[expect(clippy::similar_names, clippy::too_many_lines)] // Just a big match statement
 pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
     use ItemKind::*;
     match (l, r) {
-        (ExternCrate(l), ExternCrate(r)) => l == r,
+        (ExternCrate(ls, li), ExternCrate(rs, ri)) => ls == rs && eq_id(*li, *ri),
         (Use(l), Use(r)) => eq_use_tree(l, r),
         (
             Static(box StaticItem {
+                ident: li,
                 ty: lt,
                 mutability: lm,
                 expr: le,
@@ -339,16 +340,22 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
                 define_opaque: _,
             }),
             Static(box StaticItem {
+                ident: ri,
                 ty: rt,
                 mutability: rm,
                 expr: re,
                 safety: rs,
                 define_opaque: _,
             }),
-        ) => lm == rm && ls == rs && eq_ty(lt, rt) && eq_expr_opt(le.as_ref(), re.as_ref()),
+        ) => eq_id(*li, *ri)
+                && lm == rm
+                && ls == rs
+                && eq_ty(lt, rt)
+                && eq_expr_opt(le.as_ref(), re.as_ref()),
         (
             Const(box ConstItem {
                 defaultness: ld,
+                ident: li,
                 generics: lg,
                 ty: lt,
                 expr: le,
@@ -356,16 +363,22 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
             }),
             Const(box ConstItem {
                 defaultness: rd,
+                ident: ri,
                 generics: rg,
                 ty: rt,
                 expr: re,
                 define_opaque: _,
             }),
-        ) => eq_defaultness(*ld, *rd) && eq_generics(lg, rg) && eq_ty(lt, rt) && eq_expr_opt(le.as_ref(), re.as_ref()),
+        ) => eq_defaultness(*ld, *rd)
+                && eq_id(*li, *ri)
+                && eq_generics(lg, rg)
+                && eq_ty(lt, rt)
+                && eq_expr_opt(le.as_ref(), re.as_ref()),
         (
             Fn(box ast::Fn {
                 defaultness: ld,
                 sig: lf,
+                ident: li,
                 generics: lg,
                 contract: lc,
                 body: lb,
@@ -374,6 +387,7 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
             Fn(box ast::Fn {
                 defaultness: rd,
                 sig: rf,
+                ident: ri,
                 generics: rg,
                 contract: rc,
                 body: rb,
@@ -382,12 +396,14 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
         ) => {
             eq_defaultness(*ld, *rd)
                 && eq_fn_sig(lf, rf)
+                && eq_id(*li, *ri)
                 && eq_generics(lg, rg)
                 && eq_opt_fn_contract(lc, rc)
                 && both(lb.as_ref(), rb.as_ref(), |l, r| eq_block(l, r))
         },
-        (Mod(lu, lmk), Mod(ru, rmk)) => {
-            lu == ru
+        (Mod(ls, li, lmk), Mod(rs, ri, rmk)) => {
+            ls == rs
+                && eq_id(*li, *ri)
                 && match (lmk, rmk) {
                     (ModKind::Loaded(litems, linline, _, _), ModKind::Loaded(ritems, rinline, _, _)) => {
                         linline == rinline && over(litems, ritems, |l, r| eq_item(l, r, eq_item_kind))
@@ -421,33 +437,40 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
                 && over(lb, rb, eq_generic_bound)
                 && both(lt.as_ref(), rt.as_ref(), |l, r| eq_ty(l, r))
         },
-        (Enum(le, lg), Enum(re, rg)) => over(&le.variants, &re.variants, eq_variant) && eq_generics(lg, rg),
-        (Struct(lv, lg), Struct(rv, rg)) | (Union(lv, lg), Union(rv, rg)) => {
-            eq_variant_data(lv, rv) && eq_generics(lg, rg)
+        (Enum(li, le, lg), Enum(ri, re, rg)) => {
+            eq_id(*li, *ri) && over(&le.variants, &re.variants, eq_variant) && eq_generics(lg, rg)
+        }
+        (Struct(li, lv, lg), Struct(ri, rv, rg)) | (Union(li, lv, lg), Union(ri, rv, rg)) => {
+            eq_id(*li, *ri) && eq_variant_data(lv, rv) && eq_generics(lg, rg)
         },
         (
             Trait(box ast::Trait {
                 is_auto: la,
                 safety: lu,
+                ident: li,
                 generics: lg,
                 bounds: lb,
-                items: li,
+                items: lis,
             }),
             Trait(box ast::Trait {
                 is_auto: ra,
                 safety: ru,
+                ident: ri,
                 generics: rg,
                 bounds: rb,
-                items: ri,
+                items: ris,
             }),
         ) => {
             la == ra
                 && matches!(lu, Safety::Default) == matches!(ru, Safety::Default)
+                && eq_id(*li, *ri)
                 && eq_generics(lg, rg)
                 && over(lb, rb, eq_generic_bound)
-                && over(li, ri, |l, r| eq_item(l, r, eq_assoc_item_kind))
+                && over(lis, ris, |l, r| eq_item(l, r, eq_assoc_item_kind))
         },
-        (TraitAlias(lg, lb), TraitAlias(rg, rb)) => eq_generics(lg, rg) && over(lb, rb, eq_generic_bound),
+        (TraitAlias(li, lg, lb), TraitAlias(ri, rg, rb)) => {
+            eq_id(*li, *ri) && eq_generics(lg, rg) && over(lb, rb, eq_generic_bound)
+        }
         (
             Impl(box ast::Impl {
                 safety: lu,
@@ -480,7 +503,9 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
                 && over(li, ri, |l, r| eq_item(l, r, eq_assoc_item_kind))
         },
         (MacCall(l), MacCall(r)) => eq_mac_call(l, r),
-        (MacroDef(l), MacroDef(r)) => l.macro_rules == r.macro_rules && eq_delim_args(&l.body, &r.body),
+        (MacroDef(li, ld), MacroDef(ri, rd)) => {
+            eq_id(*li, *ri) && ld.macro_rules == rd.macro_rules && eq_delim_args(&ld.body, &rd.body)
+        }
         _ => false,
     }
 }
@@ -490,6 +515,7 @@ pub fn eq_foreign_item_kind(l: &ForeignItemKind, r: &ForeignItemKind) -> bool {
     match (l, r) {
         (
             Static(box StaticItem {
+                ident: li,
                 ty: lt,
                 mutability: lm,
                 expr: le,
@@ -497,17 +523,25 @@ pub fn eq_foreign_item_kind(l: &ForeignItemKind, r: &ForeignItemKind) -> bool {
                 define_opaque: _,
             }),
             Static(box StaticItem {
+                ident: ri,
                 ty: rt,
                 mutability: rm,
                 expr: re,
                 safety: rs,
                 define_opaque: _,
             }),
-        ) => lm == rm && eq_ty(lt, rt) && eq_expr_opt(le.as_ref(), re.as_ref()) && ls == rs,
+        ) => {
+            eq_id(*li, *ri)
+                && eq_ty(lt, rt)
+                && lm == rm
+                && eq_expr_opt(le.as_ref(), re.as_ref())
+                && ls == rs
+        }
         (
             Fn(box ast::Fn {
                 defaultness: ld,
                 sig: lf,
+                ident: li,
                 generics: lg,
                 contract: lc,
                 body: lb,
@@ -516,6 +550,7 @@ pub fn eq_foreign_item_kind(l: &ForeignItemKind, r: &ForeignItemKind) -> bool {
             Fn(box ast::Fn {
                 defaultness: rd,
                 sig: rf,
+                ident: ri,
                 generics: rg,
                 contract: rc,
                 body: rb,
@@ -524,6 +559,7 @@ pub fn eq_foreign_item_kind(l: &ForeignItemKind, r: &ForeignItemKind) -> bool {
         ) => {
             eq_defaultness(*ld, *rd)
                 && eq_fn_sig(lf, rf)
+                && eq_id(*li, *ri)
                 && eq_generics(lg, rg)
                 && eq_opt_fn_contract(lc, rc)
                 && both(lb.as_ref(), rb.as_ref(), |l, r| eq_block(l, r))
@@ -560,6 +596,7 @@ pub fn eq_assoc_item_kind(l: &AssocItemKind, r: &AssocItemKind) -> bool {
         (
             Const(box ConstItem {
                 defaultness: ld,
+                ident: li,
                 generics: lg,
                 ty: lt,
                 expr: le,
@@ -567,16 +604,24 @@ pub fn eq_assoc_item_kind(l: &AssocItemKind, r: &AssocItemKind) -> bool {
             }),
             Const(box ConstItem {
                 defaultness: rd,
+                ident: ri,
                 generics: rg,
                 ty: rt,
                 expr: re,
                 define_opaque: _,
             }),
-        ) => eq_defaultness(*ld, *rd) && eq_generics(lg, rg) && eq_ty(lt, rt) && eq_expr_opt(le.as_ref(), re.as_ref()),
+        ) => {
+            eq_defaultness(*ld, *rd)
+                && eq_id(*li, *ri)
+                && eq_generics(lg, rg)
+                && eq_ty(lt, rt)
+                && eq_expr_opt(le.as_ref(), re.as_ref())
+        }
         (
             Fn(box ast::Fn {
                 defaultness: ld,
                 sig: lf,
+                ident: li,
                 generics: lg,
                 contract: lc,
                 body: lb,
@@ -585,6 +630,7 @@ pub fn eq_assoc_item_kind(l: &AssocItemKind, r: &AssocItemKind) -> bool {
             Fn(box ast::Fn {
                 defaultness: rd,
                 sig: rf,
+                ident: ri,
                 generics: rg,
                 contract: rc,
                 body: rb,
@@ -593,6 +639,7 @@ pub fn eq_assoc_item_kind(l: &AssocItemKind, r: &AssocItemKind) -> bool {
         ) => {
             eq_defaultness(*ld, *rd)
                 && eq_fn_sig(lf, rf)
+                && eq_id(*li, *ri)
                 && eq_generics(lg, rg)
                 && eq_opt_fn_contract(lc, rc)
                 && both(lb.as_ref(), rb.as_ref(), |l, r| eq_block(l, r))