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.

Author: Noratrieb

compiler/rustc_ast_lowering/src/expr.rs

@@ -135,12 +135,16 @@ 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 =
@@ -1749,40 +1753,31 @@ 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>,
+            [] lint: rustc_hir::Lit,
         ]);
     )
 }

compiler/rustc_hir/src/hir.rs

@@ -1941,7 +1941,7 @@ 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`).
@@ -3997,6 +3997,22 @@ mod size_asserts {
     // tidy-alphabetical-end
 }
 
+mod dropless {
+    use super::*;
+
+    macro_rules! static_assert_no_destructor {
+        ($ty:ty) => {
+            const _: () = {
+                if std::mem::needs_drop::<$ty>() {
+                    panic!(concat!(stringify!($ty), " has a destructor"));
+                }
+            };
+        };
+    }
+
+    static_assert_no_destructor!(Expr<'_>);
+}
+
 fn debug_fn(f: impl Fn(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl fmt::Debug {
     struct DebugFn<F>(F);
     impl<F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result> fmt::Debug for DebugFn<F> {

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1243,7 +1243,7 @@ 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;
                 }
@@ -1302,7 +1302,7 @@ 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,