Remove `box_syntax` from AST and use in tools

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

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);

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), _)

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);
         }

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);

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);

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);
             }

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(_)

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),

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.

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

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,
+}

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

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

src/doc/unstable-book/src/language-features/box-patterns.md

@@ -4,8 +4,6 @@ The tracking issue for this feature is: [#29641]
 
 [#29641]: https://github.com/rust-lang/rust/issues/29641
 
-See also [`box_syntax`](box-syntax.md)
-
 ------------------------
 
 Box patterns let you match on `Box<T>`s:

src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs

@@ -596,8 +596,7 @@ fn ident_difference_expr_with_base_location(
         | (MethodCall(_), MethodCall(_))
         | (Call(_, _), Call(_, _))
         | (ConstBlock(_), ConstBlock(_))
-        | (Array(_), Array(_))
-        | (Box(_), Box(_)) => {
+        | (Array(_), Array(_)) => {
             // keep going
         },
         _ => {

src/tools/clippy/clippy_utils/src/ast_utils.rs

@@ -143,7 +143,7 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
         (Paren(l), _) => eq_expr(l, r),
         (_, Paren(r)) => eq_expr(l, r),
         (Err, Err) => true,
-        (Box(l), Box(r)) | (Try(l), Try(r)) | (Await(l), Await(r)) => eq_expr(l, r),
+        (Try(l), Try(r)) | (Await(l), Await(r)) => eq_expr(l, r),
         (Array(l), Array(r)) => over(l, r, |l, r| eq_expr(l, r)),
         (Tup(l), Tup(r)) => over(l, r, |l, r| eq_expr(l, r)),
         (Repeat(le, ls), Repeat(re, rs)) => eq_expr(le, re) && eq_expr(&ls.value, &rs.value),

src/tools/clippy/clippy_utils/src/sugg.rs

@@ -188,7 +188,6 @@ impl<'a> Sugg<'a> {
         match expr.kind {
             _ if expr.span.ctxt() != ctxt => Sugg::NonParen(snippet_with_context(cx, expr.span, ctxt, default, app).0),
             ast::ExprKind::AddrOf(..)
-            | ast::ExprKind::Box(..)
             | ast::ExprKind::Closure { .. }
             | ast::ExprKind::If(..)
             | ast::ExprKind::Let(..)

src/tools/rustfmt/src/closures.rs

@@ -195,7 +195,6 @@ fn rewrite_closure_expr(
             | ast::ExprKind::Struct(..) => true,
 
             ast::ExprKind::AddrOf(_, _, ref expr)
-            | ast::ExprKind::Box(ref expr)
             | ast::ExprKind::Try(ref expr)
             | ast::ExprKind::Unary(_, ref expr)
             | ast::ExprKind::Cast(ref expr, _) => allow_multi_line(expr),
@@ -441,7 +440,6 @@ fn is_block_closure_forced_inner(expr: &ast::Expr, version: Version) -> bool {
         ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop(..) => true,
         ast::ExprKind::Loop(..) if version == Version::Two => true,
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Try(ref expr)
         | ast::ExprKind::Unary(_, ref expr)
         | ast::ExprKind::Cast(ref expr, _) => is_block_closure_forced_inner(expr, version),

src/tools/rustfmt/src/expr.rs

@@ -236,7 +236,6 @@ pub(crate) fn format_expr(
         ast::ExprKind::Yeet(Some(ref expr)) => {
             rewrite_unary_prefix(context, "do yeet ", &**expr, shape)
         }
-        ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
         ast::ExprKind::AddrOf(borrow_kind, mutability, ref expr) => {
             rewrite_expr_addrof(context, borrow_kind, mutability, expr, shape)
         }
@@ -1299,7 +1298,6 @@ pub(crate) fn is_simple_expr(expr: &ast::Expr) -> bool {
         ast::ExprKind::Lit(..) => true,
         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Cast(ref expr, _)
         | ast::ExprKind::Field(ref expr, _)
         | ast::ExprKind::Try(ref expr)
@@ -1361,7 +1359,6 @@ pub(crate) fn can_be_overflowed_expr(
 
         // Handle unary-like expressions
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Try(ref expr)
         | ast::ExprKind::Unary(_, ref expr)
         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
@@ -1373,7 +1370,6 @@ pub(crate) fn is_nested_call(expr: &ast::Expr) -> bool {
     match expr.kind {
         ast::ExprKind::Call(..) | ast::ExprKind::MacCall(..) => true,
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Try(ref expr)
         | ast::ExprKind::Unary(_, ref expr)
         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
@@ -2133,7 +2129,6 @@ pub(crate) fn is_method_call(expr: &ast::Expr) -> bool {
     match expr.kind {
         ast::ExprKind::MethodCall(..) => true,
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Cast(ref expr, _)
         | ast::ExprKind::Try(ref expr)
         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),

src/tools/rustfmt/src/matches.rs

@@ -592,7 +592,6 @@ fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
         | ast::ExprKind::Struct(..)
         | ast::ExprKind::Tup(..) => true,
         ast::ExprKind::AddrOf(_, _, ref expr)
-        | ast::ExprKind::Box(ref expr)
         | ast::ExprKind::Try(ref expr)
         | ast::ExprKind::Unary(_, ref expr)
         | ast::ExprKind::Index(ref expr, _)

src/tools/rustfmt/src/utils.rs

@@ -492,7 +492,6 @@ pub(crate) fn is_block_expr(context: &RewriteContext<'_>, expr: &ast::Expr, repr
         | ast::ExprKind::Assign(..)
         | ast::ExprKind::AssignOp(..)
         | ast::ExprKind::Await(..)
-        | ast::ExprKind::Box(..)
         | ast::ExprKind::Break(..)
         | ast::ExprKind::Cast(..)
         | ast::ExprKind::Continue(..)

tests/ui/feature-gates/feature-gate-box-expr.rs

@@ -1,14 +0,0 @@
-// gate-test-box_syntax
-
-// Check that `box EXPR` is feature-gated.
-//
-// See also feature-gate-placement-expr.rs
-//
-// (Note that the two tests are separated since the checks appear to
-// be performed at distinct phases, with an abort_if_errors call
-// separating them.)
-
-fn main() {
-    let x = box 'c'; //~ ERROR box expression syntax is experimental
-    println!("x: {}", x);
-}

tests/ui/feature-gates/feature-gate-box-expr.stderr

@@ -1,12 +0,0 @@
-error[E0658]: box expression syntax is experimental; you can call `Box::new` instead
-  --> $DIR/feature-gate-box-expr.rs:12:13
-   |
-LL |     let x = box 'c';
-   |             ^^^^^^^
-   |
-   = note: see issue #49733 <https://github.com/rust-lang/rust/issues/49733> for more information
-   = help: add `#![feature(box_syntax)]` to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.

tests/ui/feature-gates/feature-gate-box_syntax.rs

@@ -1,6 +0,0 @@
-// Test that the use of the box syntax is gated by `box_syntax` feature gate.
-
-fn main() {
-    let x = box 3;
-    //~^ ERROR box expression syntax is experimental; you can call `Box::new` instead
-}

tests/ui/feature-gates/feature-gate-box_syntax.stderr

@@ -1,12 +0,0 @@
-error[E0658]: box expression syntax is experimental; you can call `Box::new` instead
-  --> $DIR/feature-gate-box_syntax.rs:4:13
-   |
-LL |     let x = box 3;
-   |             ^^^^^
-   |
-   = note: see issue #49733 <https://github.com/rust-lang/rust/issues/49733> for more information
-   = help: add `#![feature(box_syntax)]` to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.

tests/ui/parser/removed-syntax-box.rs

@@ -0,0 +1,10 @@
+fn main() {
+    struct T {
+        a: u8,
+        b: u8,
+    }
+    let _ = box () //~ ERROR expected expression, found reserved keyword `box`
+    let _ = box 1;
+    let _ = box T { a: 12, b: 18 };
+    let _ = box [5; 30];
+}

tests/ui/parser/removed-syntax-box.stderr

@@ -0,0 +1,8 @@
+error: expected expression, found reserved keyword `box`
+  --> $DIR/removed-syntax-box.rs:6:13
+   |
+LL |     let _ = box ()
+   |             ^^^ expected expression
+
+error: aborting due to previous error
+