Reduce `P<T>` to a typedef of `Box<T>`.

Keep the `P` constructor function for now, to minimize immediate churn.

All the `into_inner` calls are removed, which is nice.

15 files changed, 48 insertions, 131 deletions

diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index f165c4ddcdd..621e3042b62 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -63,7 +63,7 @@ impl Attribute {
 
     pub fn unwrap_normal_item(self) -> AttrItem {
         match self.kind {
-            AttrKind::Normal(normal) => normal.into_inner().item,
+            AttrKind::Normal(normal) => normal.item,
             AttrKind::DocComment(..) => panic!("unexpected doc comment"),
         }
     }
diff --git a/compiler/rustc_ast/src/ptr.rs b/compiler/rustc_ast/src/ptr.rs
index 91f29a4c289..fffeab8bbca 100644
--- a/compiler/rustc_ast/src/ptr.rs
+++ b/compiler/rustc_ast/src/ptr.rs
@@ -1,81 +1,11 @@
-//! The AST pointer.
-//!
-//! Provides [`P<T>`][struct@P], an owned smart pointer.
-//!
-//! # Motivations and benefits
-//!
-//! * **Identity**: sharing AST nodes is problematic for the various analysis
-//!   passes (e.g., one may be able to bypass the borrow checker with a shared
-//!   `ExprKind::AddrOf` node taking a mutable borrow).
-//!
-//! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`,
-//!   the latter even when the input and output types differ (as it would be the
-//!   case with arenas or a GADT AST using type parameters to toggle features).
-//!
-//! * **Maintainability**: `P<T>` provides an interface, which can remain fully
-//!   functional even if the implementation changes (using a special thread-local
-//!   heap, for example). Moreover, a switch to, e.g., `P<'a, T>` would be easy
-//!   and mostly automated.
-
-use std::fmt::{self, Debug};
-use std::ops::{Deref, DerefMut};
-
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
-
-/// An owned smart pointer.
+/// A pointer type that uniquely owns a heap allocation of type T.
 ///
-/// See the [module level documentation][crate::ptr] for details.
-pub struct P<T: ?Sized> {
-    ptr: Box<T>,
-}
+/// This used to be its own type, but now it's just a typedef for `Box` and we are planning to
+/// remove it soon.
+pub type P<T> = Box<T>;
 
 /// Construct a `P<T>` from a `T` value.
 #[allow(non_snake_case)]
 pub fn P<T>(value: T) -> P<T> {
-    P { ptr: Box::new(value) }
-}
-
-impl<T> P<T> {
-    /// Consume the `P` and return the wrapped value.
-    pub fn into_inner(self) -> T {
-        *self.ptr
-    }
-}
-
-impl<T: ?Sized> Deref for P<T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        &self.ptr
-    }
-}
-
-impl<T: ?Sized> DerefMut for P<T> {
-    fn deref_mut(&mut self) -> &mut T {
-        &mut self.ptr
-    }
-}
-
-impl<T: Clone> Clone for P<T> {
-    fn clone(&self) -> P<T> {
-        P((**self).clone())
-    }
-}
-
-impl<T: ?Sized + Debug> Debug for P<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        Debug::fmt(&self.ptr, f)
-    }
-}
-
-impl<D: Decoder, T: Decodable<D>> Decodable<D> for P<T> {
-    fn decode(d: &mut D) -> P<T> {
-        P(Decodable::decode(d))
-    }
-}
-
-impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<T> {
-    fn encode(&self, s: &mut S) {
-        (**self).encode(s);
-    }
+    Box::new(value)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/mod.rs b/compiler/rustc_builtin_macros/src/deriving/mod.rs
index 50e7b989ed8..e45d09b5796 100644
--- a/compiler/rustc_builtin_macros/src/deriving/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/mod.rs
@@ -57,7 +57,7 @@ impl MultiItemModifier for BuiltinDerive {
         let mut items = Vec::new();
         match item {
             Annotatable::Stmt(stmt) => {
-                if let ast::StmtKind::Item(item) = stmt.into_inner().kind {
+                if let ast::StmtKind::Item(item) = stmt.kind {
                     (self.0)(
                         ecx,
                         span,
diff --git a/compiler/rustc_builtin_macros/src/pattern_type.rs b/compiler/rustc_builtin_macros/src/pattern_type.rs
index 3529e5525fc..b61af0b0aaa 100644
--- a/compiler/rustc_builtin_macros/src/pattern_type.rs
+++ b/compiler/rustc_builtin_macros/src/pattern_type.rs
@@ -30,14 +30,12 @@ fn parse_pat_ty<'a>(cx: &mut ExtCtxt<'a>, stream: TokenStream) -> PResult<'a, (P
 
     let pat = pat_to_ty_pat(
         cx,
-        parser
-            .parse_pat_no_top_guard(
-                None,
-                RecoverComma::No,
-                RecoverColon::No,
-                CommaRecoveryMode::EitherTupleOrPipe,
-            )?
-            .into_inner(),
+        *parser.parse_pat_no_top_guard(
+            None,
+            RecoverComma::No,
+            RecoverColon::No,
+            CommaRecoveryMode::EitherTupleOrPipe,
+        )?,
     );
 
     if parser.token != token::Eof {
@@ -58,9 +56,9 @@ fn pat_to_ty_pat(cx: &mut ExtCtxt<'_>, pat: ast::Pat) -> P<TyPat> {
             end.map(|value| P(AnonConst { id: DUMMY_NODE_ID, value })),
             include_end,
         ),
-        ast::PatKind::Or(variants) => TyPatKind::Or(
-            variants.into_iter().map(|pat| pat_to_ty_pat(cx, pat.into_inner())).collect(),
-        ),
+        ast::PatKind::Or(variants) => {
+            TyPatKind::Or(variants.into_iter().map(|pat| pat_to_ty_pat(cx, *pat)).collect())
+        }
         ast::PatKind::Err(guar) => TyPatKind::Err(guar),
         _ => TyPatKind::Err(cx.dcx().span_err(pat.span, "pattern not supported in pattern types")),
     };
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index fbe91531e5a..b439fa34f5b 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -40,7 +40,7 @@ pub(crate) fn expand_test_case(
     let (mut item, is_stmt) = match anno_item {
         Annotatable::Item(item) => (item, false),
         Annotatable::Stmt(stmt) if let ast::StmtKind::Item(_) = stmt.kind => {
-            if let ast::StmtKind::Item(i) = stmt.into_inner().kind {
+            if let ast::StmtKind::Item(i) = stmt.kind {
                 (i, true)
             } else {
                 unreachable!()
@@ -120,11 +120,7 @@ pub(crate) fn expand_test_or_bench(
         Annotatable::Item(i) => (i, false),
         Annotatable::Stmt(stmt) if matches!(stmt.kind, ast::StmtKind::Item(_)) => {
             // FIXME: Use an 'if let' guard once they are implemented
-            if let ast::StmtKind::Item(i) = stmt.into_inner().kind {
-                (i, true)
-            } else {
-                unreachable!()
-            }
+            if let ast::StmtKind::Item(i) = stmt.kind { (i, true) } else { unreachable!() }
         }
         other => {
             not_testable_error(cx, attr_sp, None);
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 55751aa4908..058e45cdc4c 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -167,7 +167,7 @@ impl Annotatable {
 
     pub fn expect_stmt(self) -> ast::Stmt {
         match self {
-            Annotatable::Stmt(stmt) => stmt.into_inner(),
+            Annotatable::Stmt(stmt) => *stmt,
             _ => panic!("expected statement"),
         }
     }
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 81d4d59ee04..4c7bc912f8f 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -1188,9 +1188,8 @@ impl InvocationCollectorNode for P<ast::Item> {
         matches!(self.kind, ItemKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.into_inner();
-        match node.kind {
-            ItemKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
+        match self.kind {
+            ItemKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
         }
     }
@@ -1344,7 +1343,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag>
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let item = self.wrapped.into_inner();
+        let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1385,7 +1384,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag>
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let item = self.wrapped.into_inner();
+        let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1426,7 +1425,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitImplItem
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let item = self.wrapped.into_inner();
+        let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1464,9 +1463,8 @@ impl InvocationCollectorNode for P<ast::ForeignItem> {
         matches!(self.kind, ForeignItemKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.into_inner();
-        match node.kind {
-            ForeignItemKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
+        match self.kind {
+            ForeignItemKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
         }
     }
@@ -1601,16 +1599,16 @@ impl InvocationCollectorNode for ast::Stmt {
         // `StmtKind`s and treat them as statement macro invocations, not as items or expressions.
         let (add_semicolon, mac, attrs) = match self.kind {
             StmtKind::MacCall(mac) => {
-                let ast::MacCallStmt { mac, style, attrs, .. } = mac.into_inner();
+                let ast::MacCallStmt { mac, style, attrs, .. } = *mac;
                 (style == MacStmtStyle::Semicolon, mac, attrs)
             }
-            StmtKind::Item(item) => match item.into_inner() {
+            StmtKind::Item(item) => match *item {
                 ast::Item { kind: ItemKind::MacCall(mac), attrs, .. } => {
                     (mac.args.need_semicolon(), mac, attrs)
                 }
                 _ => unreachable!(),
             },
-            StmtKind::Semi(expr) => match expr.into_inner() {
+            StmtKind::Semi(expr) => match *expr {
                 ast::Expr { kind: ExprKind::MacCall(mac), attrs, .. } => {
                     (mac.args.need_semicolon(), mac, attrs)
                 }
@@ -1691,8 +1689,7 @@ impl InvocationCollectorNode for P<ast::Ty> {
         matches!(self.kind, ast::TyKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.into_inner();
-        match node.kind {
+        match self.kind {
             TyKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
             _ => unreachable!(),
         }
@@ -1715,8 +1712,7 @@ impl InvocationCollectorNode for P<ast::Pat> {
         matches!(self.kind, PatKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.into_inner();
-        match node.kind {
+        match self.kind {
             PatKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
             _ => unreachable!(),
         }
@@ -1742,9 +1738,8 @@ impl InvocationCollectorNode for P<ast::Expr> {
         matches!(self.kind, ExprKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.into_inner();
-        match node.kind {
-            ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
+        match self.kind {
+            ExprKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
         }
     }
@@ -1768,7 +1763,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.wrapped.into_inner();
+        let node = self.wrapped;
         match node.kind {
             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1806,7 +1801,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, MethodReceiverTag>
         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
     }
     fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
-        let node = self.wrapped.into_inner();
+        let node = self.wrapped;
         match node.kind {
             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
             _ => unreachable!(),
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 6277dde7c97..b49a13ce584 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2273,9 +2273,9 @@ impl<'a> Parser<'a> {
                     ),
                     // Also catches `fn foo(&a)`.
                     PatKind::Ref(ref inner_pat, mutab)
-                        if matches!(inner_pat.clone().into_inner().kind, PatKind::Ident(..)) =>
+                        if matches!(inner_pat.clone().kind, PatKind::Ident(..)) =>
                     {
-                        match inner_pat.clone().into_inner().kind {
+                        match inner_pat.clone().kind {
                             PatKind::Ident(_, ident, _) => {
                                 let mutab = mutab.prefix_str();
                                 (
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 6e134bad7bd..5824c2aa405 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -3450,10 +3450,8 @@ impl<'a> Parser<'a> {
                 // Detect and recover from `($pat if $cond) => $arm`.
                 // FIXME(guard_patterns): convert this to a normal guard instead
                 let span = pat.span;
-                let ast::PatKind::Paren(subpat) = pat.into_inner().kind else { unreachable!() };
-                let ast::PatKind::Guard(_, mut cond) = subpat.into_inner().kind else {
-                    unreachable!()
-                };
+                let ast::PatKind::Paren(subpat) = pat.kind else { unreachable!() };
+                let ast::PatKind::Guard(_, mut cond) = subpat.kind else { unreachable!() };
                 self.psess.gated_spans.ungate_last(sym::guard_patterns, cond.span);
                 CondChecker::new(self, LetChainsPolicy::AlwaysAllowed).visit_expr(&mut cond);
                 let right = self.prev_token.span;
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index babc55ccc0f..e9654e61eb8 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -145,7 +145,7 @@ impl<'a> Parser<'a> {
         {
             let mut item = item.expect("an actual item");
             attrs.prepend_to_nt_inner(&mut item.attrs);
-            return Ok(Some(item.into_inner()));
+            return Ok(Some(*item));
         }
 
         self.collect_tokens(None, attrs, force_collect, |this, mut attrs| {
@@ -637,7 +637,7 @@ impl<'a> Parser<'a> {
                     self.dcx().emit_err(errors::MissingForInTraitImpl { span: missing_for_span });
                 }
 
-                let ty_first = ty_first.into_inner();
+                let ty_first = *ty_first;
                 let path = match ty_first.kind {
                     // This notably includes paths passed through `ty` macro fragments (#46438).
                     TyKind::Path(None, path) => path,
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index d6ff80b2eb4..7a226136e23 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1086,7 +1086,7 @@ impl<'a> Parser<'a> {
         if matches!(pat.kind, PatKind::Ident(BindingMode(ByRef::Yes(_), Mutability::Mut), ..)) {
             self.psess.gated_spans.gate(sym::mut_ref, pat.span);
         }
-        Ok(pat.into_inner().kind)
+        Ok(pat.kind)
     }
 
     /// Turn all by-value immutable bindings in a pattern into mutable bindings.
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 17481731b11..460cf23c393 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -404,7 +404,7 @@ impl<'a> Parser<'a> {
         })?;
 
         if ts.len() == 1 && matches!(trailing, Trailing::No) {
-            let ty = ts.into_iter().next().unwrap().into_inner();
+            let ty = ts.into_iter().next().unwrap();
             let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
             match ty.kind {
                 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
@@ -420,7 +420,7 @@ impl<'a> Parser<'a> {
                     self.parse_remaining_bounds(bounds, true)
                 }
                 // `(TYPE)`
-                _ => Ok(TyKind::Paren(P(ty))),
+                _ => Ok(TyKind::Paren(ty)),
             }
         } else {
             Ok(TyKind::Tup(ts))
@@ -1295,7 +1295,7 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, ()> {
         let fn_path_segment = fn_path.segments.last_mut().unwrap();
         let generic_args = if let Some(p_args) = &fn_path_segment.args {
-            p_args.clone().into_inner()
+            *p_args.clone()
         } else {
             // Normally it wouldn't come here because the upstream should have parsed
             // generic parameters (otherwise it's impossible to call this function).
diff --git a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
index 9ad184450de..b839b6f5672 100644
--- a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
+++ b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
@@ -426,7 +426,7 @@ fn drain_matching(
         // Check if we should extract, but only if `idx >= start`.
         if idx > start && predicate(&alternatives[i].kind) {
             let pat = alternatives.remove(i);
-            tail_or.push(extract(pat.into_inner().kind));
+            tail_or.push(extract(pat.kind));
         } else {
             i += 1;
         }
diff --git a/src/tools/rustfmt/src/modules.rs b/src/tools/rustfmt/src/modules.rs
index bc5a6d3e704..44c8123517c 100644
--- a/src/tools/rustfmt/src/modules.rs
+++ b/src/tools/rustfmt/src/modules.rs
@@ -174,7 +174,7 @@ impl<'ast, 'psess, 'c> ModResolver<'ast, 'psess> {
     ) -> Result<(), ModuleResolutionError> {
         for item in items {
             if is_cfg_if(&item) {
-                self.visit_cfg_if(Cow::Owned(item.into_inner()))?;
+                self.visit_cfg_if(Cow::Owned(*item))?;
                 continue;
             }
 
diff --git a/src/tools/rustfmt/src/parse/macros/cfg_if.rs b/src/tools/rustfmt/src/parse/macros/cfg_if.rs
index 30b83373c17..26bf6c5326f 100644
--- a/src/tools/rustfmt/src/parse/macros/cfg_if.rs
+++ b/src/tools/rustfmt/src/parse/macros/cfg_if.rs
@@ -62,7 +62,7 @@ fn parse_cfg_if_inner<'a>(
 
         while parser.token != TokenKind::CloseBrace && parser.token.kind != TokenKind::Eof {
             let item = match parser.parse_item(ForceCollect::No) {
-                Ok(Some(item_ptr)) => item_ptr.into_inner(),
+                Ok(Some(item_ptr)) => *item_ptr,
                 Ok(None) => continue,
                 Err(err) => {
                     err.cancel();