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`.

1 files changed, 20 insertions, 26 deletions

diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
index 768b459ec5e..56a67b0534d 100644
--- a/compiler/rustc_builtin_macros/src/test_harness.rs
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -134,7 +134,8 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
         if let Some(name) = get_test_name(&item) {
             debug!("this is a test item");
 
-            let test = Test { span: item.span, ident: item.ident, name };
+            // `unwrap` is ok because only functions, consts, and static should reach here.
+            let test = Test { span: item.span, ident: item.kind.ident().unwrap(), name };
             self.tests.push(test);
         }
 
@@ -142,19 +143,12 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
         // mods or tests inside of functions will break things
         if let ast::ItemKind::Mod(
             _,
+            _,
             ModKind::Loaded(.., ast::ModSpans { inner_span: span, .. }, _),
         ) = item.kind
         {
             let prev_tests = mem::take(&mut self.tests);
-            walk_item_kind(
-                &mut item.kind,
-                item.span,
-                item.id,
-                &mut item.ident,
-                &mut item.vis,
-                (),
-                self,
-            );
+            walk_item_kind(&mut item.kind, item.span, item.id, &mut item.vis, (), self);
             self.add_test_cases(item.id, span, prev_tests);
         } else {
             // But in those cases, we emit a lint to warn the user of these missing tests.
@@ -181,9 +175,9 @@ impl<'a> Visitor<'a> for InnerItemLinter<'_> {
 }
 
 fn entry_point_type(item: &ast::Item, at_root: bool) -> EntryPointType {
-    match item.kind {
-        ast::ItemKind::Fn(..) => {
-            rustc_ast::entry::entry_point_type(&item.attrs, at_root, Some(item.ident.name))
+    match &item.kind {
+        ast::ItemKind::Fn(fn_) => {
+            rustc_ast::entry::entry_point_type(&item.attrs, at_root, Some(fn_.ident.name))
         }
         _ => EntryPointType::None,
     }
@@ -295,7 +289,7 @@ fn generate_test_harness(
 fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     let sp = cx.def_site;
     let ecx = &cx.ext_cx;
-    let test_id = Ident::new(sym::test, sp);
+    let test_ident = Ident::new(sym::test, sp);
 
     let runner_name = match cx.panic_strategy {
         PanicStrategy::Unwind => "test_main_static",
@@ -303,10 +297,9 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     };
 
     // test::test_main_static(...)
-    let mut test_runner = cx
-        .test_runner
-        .clone()
-        .unwrap_or_else(|| ecx.path(sp, vec![test_id, Ident::from_str_and_span(runner_name, sp)]));
+    let mut test_runner = cx.test_runner.clone().unwrap_or_else(|| {
+        ecx.path(sp, vec![test_ident, Ident::from_str_and_span(runner_name, sp)])
+    });
 
     test_runner.span = sp;
 
@@ -317,7 +310,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     // extern crate test
     let test_extern_stmt = ecx.stmt_item(
         sp,
-        ecx.item(sp, test_id, ast::AttrVec::new(), ast::ItemKind::ExternCrate(None)),
+        ecx.item(sp, ast::AttrVec::new(), ast::ItemKind::ExternCrate(None, test_ident)),
     );
 
     // #[rustc_main]
@@ -340,23 +333,24 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     let decl = ecx.fn_decl(ThinVec::new(), ast::FnRetTy::Ty(main_ret_ty));
     let sig = ast::FnSig { decl, header: ast::FnHeader::default(), span: sp };
     let defaultness = ast::Defaultness::Final;
+
+    // Honor the reexport_test_harness_main attribute
+    let main_ident = match cx.reexport_test_harness_main {
+        Some(sym) => Ident::new(sym, sp.with_ctxt(SyntaxContext::root())),
+        None => Ident::new(sym::main, sp),
+    };
+
     let main = ast::ItemKind::Fn(Box::new(ast::Fn {
         defaultness,
         sig,
+        ident: main_ident,
         generics: ast::Generics::default(),
         contract: None,
         body: Some(main_body),
         define_opaque: None,
     }));
 
-    // Honor the reexport_test_harness_main attribute
-    let main_id = match cx.reexport_test_harness_main {
-        Some(sym) => Ident::new(sym, sp.with_ctxt(SyntaxContext::root())),
-        None => Ident::new(sym::main, sp),
-    };
-
     let main = P(ast::Item {
-        ident: main_id,
         attrs: thin_vec![main_attr, coverage_attr, doc_hidden_attr],
         id: ast::DUMMY_NODE_ID,
         kind: main,