Remove `box_syntax` from AST and use in tools

14 files changed, 20 insertions, 36 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 03c375c4666..6503bf2bab7 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1230,7 +1230,6 @@ impl Expr {
 
     pub fn precedence(&self) -> ExprPrecedence {
         match self.kind {
-            ExprKind::Box(_) => ExprPrecedence::Box,
             ExprKind::Array(_) => ExprPrecedence::Array,
             ExprKind::ConstBlock(_) => ExprPrecedence::ConstBlock,
             ExprKind::Call(..) => ExprPrecedence::Call,
@@ -1291,8 +1290,7 @@ impl Expr {
     /// To a first-order approximation, is this a pattern?
     pub fn is_approximately_pattern(&self) -> bool {
         match &self.peel_parens().kind {
-            ExprKind::Box(_)
-            | ExprKind::Array(_)
+            ExprKind::Array(_)
             | ExprKind::Call(_, _)
             | ExprKind::Tup(_)
             | ExprKind::Lit(_)
@@ -1363,8 +1361,6 @@ pub struct StructExpr {
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum ExprKind {
-    /// A `box x` expression.
-    Box(P<Expr>),
     /// An array (`[a, b, c, d]`)
     Array(ThinVec<P<Expr>>),
     /// Allow anonymous constants from an inline `const` block
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 6fed0b660e8..45a5a3ecb53 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1316,7 +1316,6 @@ pub fn noop_visit_expr<T: MutVisitor>(
     vis: &mut T,
 ) {
     match kind {
-        ExprKind::Box(expr) => vis.visit_expr(expr),
         ExprKind::Array(exprs) => visit_thin_exprs(exprs, vis),
         ExprKind::ConstBlock(anon_const) => {
             vis.visit_anon_const(anon_const);
diff --git a/compiler/rustc_ast/src/util/classify.rs b/compiler/rustc_ast/src/util/classify.rs
index cdc244c1218..607b77705cf 100644
--- a/compiler/rustc_ast/src/util/classify.rs
+++ b/compiler/rustc_ast/src/util/classify.rs
@@ -35,7 +35,6 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<&ast::Expr> {
             | Assign(_, e, _)
             | AssignOp(_, _, e)
             | Binary(_, _, e)
-            | Box(e)
             | Break(_, Some(e))
             | Let(_, e, _)
             | Range(_, Some(e), _)
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index bdb1879ec20..9a4da6d4396 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -772,7 +772,6 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
     walk_list!(visitor, visit_attribute, expression.attrs.iter());
 
     match &expression.kind {
-        ExprKind::Box(subexpression) => visitor.visit_expr(subexpression),
         ExprKind::Array(subexpressions) => {
             walk_list!(visitor, visit_expr, subexpressions);
         }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index ffb30b1b391..4390680c45a 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -70,7 +70,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
             self.lower_attrs(hir_id, &e.attrs);
 
             let kind = match &e.kind {
-                ExprKind::Box(inner) => hir::ExprKind::Box(self.lower_expr(inner)),
                 ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
                 ExprKind::ConstBlock(anon_const) => {
                     let anon_const = self.lower_anon_const(anon_const);
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 96042ea3078..109f83d4d18 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -395,14 +395,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_expr(&mut self, e: &'a ast::Expr) {
         match e.kind {
-            ast::ExprKind::Box(_) => {
-                gate_feature_post!(
-                    &self,
-                    box_syntax,
-                    e.span,
-                    "box expression syntax is experimental; you can call `Box::new` instead"
-                );
-            }
             ast::ExprKind::Type(..) => {
                 if self.sess.parse_sess.span_diagnostic.err_count() == 0 {
                     // To avoid noise about type ascription in common syntax errors,
@@ -613,7 +605,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(box_patterns, "box pattern syntax is experimental");
     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
     gate_all!(try_blocks, "`try` blocks are unstable");
-    gate_all!(box_syntax, "box expression syntax is experimental; you can call `Box::new` instead");
     gate_all!(type_ascription, "type ascription is experimental");
 
     visit::walk_crate(&mut visitor, krate);
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index a4d91a95662..e2f63641ffa 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -296,10 +296,6 @@ impl<'a> State<'a> {
         self.ibox(INDENT_UNIT);
         self.ann.pre(self, AnnNode::Expr(expr));
         match &expr.kind {
-            ast::ExprKind::Box(expr) => {
-                self.word_space("box");
-                self.print_expr_maybe_paren(expr, parser::PREC_PREFIX);
-            }
             ast::ExprKind::Array(exprs) => {
                 self.print_expr_vec(exprs);
             }
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index b0b4dda16af..5d8f4db76f9 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -290,7 +290,6 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::Async(_, _, _)
             | ExprKind::Await(_)
             | ExprKind::Block(_, _)
-            | ExprKind::Box(_)
             | ExprKind::Break(_, _)
             | ExprKind::Closure(_)
             | ExprKind::ConstBlock(_)
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 2fa7bceb8bc..c893b34b4ac 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -200,8 +200,6 @@ declare_features! (
     (active, auto_traits, "1.50.0", Some(13231), None),
     /// Allows using `box` in patterns (RFC 469).
     (active, box_patterns, "1.0.0", Some(29641), None),
-    /// Allows using the `box $expr` syntax.
-    (active, box_syntax, "1.0.0", Some(49733), None),
     /// Allows `#[doc(notable_trait)]`.
     /// Renamed from `doc_spotlight`.
     (active, doc_notable_trait, "1.52.0", Some(45040), None),
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index 04d4f6cb14e..48d9fbfa6d2 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -52,6 +52,8 @@ declare_features! (
     (removed, allow_fail, "1.19.0", Some(46488), None, Some("removed due to no clear use cases")),
     (removed, await_macro, "1.38.0", Some(50547), None,
      Some("subsumed by `.await` syntax")),
+    /// Allows using the `box $expr` syntax.
+    (removed, box_syntax, "CURRENT_RUSTC_VERSION", Some(49733), None, Some("replaced with `#[rustc_box]`")),
     /// Allows capturing disjoint fields in a closure/generator (RFC 2229).
     (removed, capture_disjoint_fields, "1.49.0", Some(53488), None, Some("stabilized in Rust 2021")),
     /// Allows comparing raw pointers during const eval.
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index ab7931d74d7..c39ada95a4e 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -731,3 +731,6 @@ parse_unknown_start_of_token = unknown start of token: {$escaped}
         [one] once more
         *[other] {$repeats} more times
     }
+
+parse_box_syntax_removed = `box_syntax` has been removed
+    .suggestion = use `Box::new()` instead
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 63e5bc50513..af0c3026c66 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -2300,3 +2300,16 @@ impl HelpUseLatestEdition {
         }
     }
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_box_syntax_removed)]
+pub struct BoxSyntaxRemoved<'a> {
+    #[primary_span]
+    #[suggestion(
+        code = "Box::new({code})",
+        applicability = "machine-applicable",
+        style = "verbose"
+    )]
+    pub span: Span,
+    pub code: &'a str,
+}
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index e00eda47c66..27516716286 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -607,9 +607,6 @@ impl<'a> Parser<'a> {
                 let operand_expr = this.parse_expr_dot_or_call(Default::default())?;
                 this.recover_from_prefix_increment(operand_expr, pre_span, starts_stmt)
             }
-            token::Ident(..) if this.token.is_keyword(kw::Box) => {
-                make_it!(this, attrs, |this, _| this.parse_expr_box(lo))
-            }
             token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
             }
@@ -636,13 +633,6 @@ impl<'a> Parser<'a> {
         self.parse_expr_unary(lo, UnOp::Not)
     }
 
-    /// Parse `box expr`.
-    fn parse_expr_box(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
-        let (span, expr) = self.parse_expr_prefix_common(lo)?;
-        self.sess.gated_spans.gate(sym::box_syntax, span);
-        Ok((span, ExprKind::Box(expr)))
-    }
-
     fn is_mistaken_not_ident_negation(&self) -> bool {
         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
             // These tokens can start an expression after `!`, but
diff --git a/compiler/rustc_passes/src/hir_stats.rs b/compiler/rustc_passes/src/hir_stats.rs
index 5e2d2d3e5a7..3e0d53029ef 100644
--- a/compiler/rustc_passes/src/hir_stats.rs
+++ b/compiler/rustc_passes/src/hir_stats.rs
@@ -565,7 +565,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
         record_variants!(
             (self, e, e.kind, Id::None, ast, Expr, ExprKind),
             [
-                Box, Array, ConstBlock, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, Let,
+                Array, ConstBlock, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, Let,
                 If, While, ForLoop, Loop, Match, Closure, Block, Async, Await, TryBlock, Assign,
                 AssignOp, Field, Index, Range, Underscore, Path, AddrOf, Break, Continue, Ret,
                 InlineAsm, FormatArgs, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet, IncludedBytes, Err