Alloc hir::Lit in an arena to remove the destructor from Expr

This allows allocating `Expr`s into a dropless arena, which is useful
for using length prefixed thing slices in HIR, since these can only be
allocated in the dropless arena and not in a typed arena. This is
something I'm working on.

compiler/rustc_ast_lowering/src/expr.rs

@@ -121,12 +121,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             LitKind::Err
                         }
                     };
-                    hir::ExprKind::Lit(respan(self.lower_span(e.span), lit_kind))
+                    let lit = self.arena.alloc(respan(self.lower_span(e.span), lit_kind));
+                    hir::ExprKind::Lit(lit)
+                }
+                ExprKind::IncludedBytes(bytes) => {
+                    let lit = self.arena.alloc(respan(
+                        self.lower_span(e.span),
+                        LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
+                    ));
+                    hir::ExprKind::Lit(lit)
                 }
-                ExprKind::IncludedBytes(bytes) => hir::ExprKind::Lit(respan(
-                    self.lower_span(e.span),
-                    LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
-                )),
                 ExprKind::Cast(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
@@ -1746,40 +1750,31 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     pub(super) fn expr_usize(&mut self, sp: Span, value: usize) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Int(
-                    value as u128,
-                    ast::LitIntType::Unsigned(ast::UintTy::Usize),
-                ),
-            }),
-        )
+        let lit = self.arena.alloc(hir::Lit {
+            span: sp,
+            node: ast::LitKind::Int(value as u128, ast::LitIntType::Unsigned(ast::UintTy::Usize)),
+        });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_u32(&mut self, sp: Span, value: u32) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Int(value.into(), ast::LitIntType::Unsigned(ast::UintTy::U32)),
-            }),
-        )
+        let lit = self.arena.alloc(hir::Lit {
+            span: sp,
+            node: ast::LitKind::Int(value.into(), ast::LitIntType::Unsigned(ast::UintTy::U32)),
+        });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_char(&mut self, sp: Span, value: char) -> hir::Expr<'hir> {
-        self.expr(sp, hir::ExprKind::Lit(hir::Lit { span: sp, node: ast::LitKind::Char(value) }))
+        let lit = self.arena.alloc(hir::Lit { span: sp, node: ast::LitKind::Char(value) });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_str(&mut self, sp: Span, value: Symbol) -> hir::Expr<'hir> {
-        self.expr(
-            sp,
-            hir::ExprKind::Lit(hir::Lit {
-                span: sp,
-                node: ast::LitKind::Str(value, ast::StrStyle::Cooked),
-            }),
-        )
+        let lit = self
+            .arena
+            .alloc(hir::Lit { span: sp, node: ast::LitKind::Str(value, ast::StrStyle::Cooked) });
+        self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
     pub(super) fn expr_call_mut(

compiler/rustc_hir/src/arena.rs

@@ -51,6 +51,7 @@ macro_rules! arena_types {
             [] type_binding: rustc_hir::TypeBinding<'tcx>,
             [] variant: rustc_hir::Variant<'tcx>,
             [] where_predicate: rustc_hir::WherePredicate<'tcx>,
+            [] lit: rustc_hir::Lit,
         ]);
     )
 }

compiler/rustc_hir/src/hir.rs

@@ -1957,7 +1957,7 @@ pub enum ExprKind<'hir> {
     /// A unary operation (e.g., `!x`, `*x`).
     Unary(UnOp, &'hir Expr<'hir>),
     /// A literal (e.g., `1`, `"foo"`).
-    Lit(Lit),
+    Lit(&'hir Lit),
     /// A cast (e.g., `foo as f64`).
     Cast(&'hir Expr<'hir>, &'hir Ty<'hir>),
     /// A type reference (e.g., `Foo`).

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1252,7 +1252,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 node: rustc_ast::LitKind::Int(lit, rustc_ast::LitIntType::Unsuffixed),
                 span,
             }) => {
-                let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) else { return false; };
+                let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(*span) else { return false; };
                 if !(snippet.starts_with("0x") || snippet.starts_with("0X")) {
                     return false;
                 }
@@ -1311,7 +1311,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // We have satisfied all requirements to provide a suggestion. Emit it.
         err.span_suggestion(
-            span,
+            *span,
             format!("if you meant to create a null pointer, use `{null_path_str}()`"),
             null_path_str + "()",
             Applicability::MachineApplicable,

src/tools/clippy/clippy_lints/src/bool_assert_comparison.rs

@@ -41,7 +41,7 @@ fn extract_bool_lit(e: &Expr<'_>) -> Option<bool> {
     }) = e.kind
         && !e.span.from_expansion()
     {
-        Some(b)
+        Some(*b)
     } else {
         None
     }

src/tools/clippy/clippy_lints/src/manual_strip.rs

@@ -159,7 +159,7 @@ fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'t
         ..
     }) = expr.kind
     {
-        constant_length(cx, pattern).map_or(false, |length| length == n)
+        constant_length(cx, pattern).map_or(false, |length| length == *n)
     } else {
         len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
     }

src/tools/clippy/clippy_lints/src/matches/match_like_matches.rs

@@ -162,7 +162,7 @@ fn find_bool_lit(ex: &ExprKind<'_>) -> Option<bool> {
                 node: LitKind::Bool(b), ..
             }) = exp.kind
             {
-                Some(b)
+                Some(*b)
             } else {
                 None
             }

src/tools/clippy/clippy_lints/src/methods/open_options.rs

@@ -48,7 +48,7 @@ fn get_open_options(cx: &LateContext<'_>, argument: &Expr<'_>, options: &mut Vec
                         ..
                     } = *span
                     {
-                        if lit { Argument::True } else { Argument::False }
+                        if *lit { Argument::True } else { Argument::False }
                     } else {
                         // The function is called with a literal which is not a boolean literal.
                         // This is theoretically possible, but not very likely.

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -430,7 +430,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 kind!("Unary(UnOp::{op:?}, {inner})");
                 self.expr(inner);
             },
-            ExprKind::Lit(ref lit) => {
+            ExprKind::Lit(lit) => {
                 bind!(self, lit);
                 kind!("Lit(ref {lit})");
                 self.lit(lit);