parse const closures

16 files changed, 63 insertions, 12 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index e656fb3740b..7de594719dd 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1307,6 +1307,7 @@ impl Expr {
 pub struct Closure {
     pub binder: ClosureBinder,
     pub capture_clause: CaptureBy,
+    pub constness: Const,
     pub asyncness: Async,
     pub movability: Movability,
     pub fn_decl: P<FnDecl>,
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index c572171e8f4..77f342d1eb3 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1362,6 +1362,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         ExprKind::Closure(box Closure {
             binder,
             capture_clause: _,
+            constness,
             asyncness,
             movability: _,
             fn_decl,
@@ -1370,6 +1371,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             fn_arg_span: _,
         }) => {
             vis.visit_closure_binder(binder);
+            visit_constness(constness, vis);
             vis.visit_asyncness(asyncness);
             vis.visit_fn_decl(fn_decl);
             vis.visit_expr(body);
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index df7145a722a..e8823eff83a 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -836,6 +836,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             binder,
             capture_clause: _,
             asyncness: _,
+            constness: _,
             movability: _,
             fn_decl,
             body,
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 14f082be9ba..c3611b2f522 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -209,6 +209,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::Closure(box Closure {
                     binder,
                     capture_clause,
+                    constness,
                     asyncness,
                     movability,
                     fn_decl,
@@ -233,6 +234,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             binder,
                             *capture_clause,
                             e.id,
+                            *constness,
                             *movability,
                             fn_decl,
                             body,
@@ -651,6 +653,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 fn_decl_span: self.lower_span(span),
                 fn_arg_span: None,
                 movability: Some(hir::Movability::Static),
+                constness: hir::Constness::NotConst,
             });
 
             hir::ExprKind::Closure(c)
@@ -890,6 +893,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         binder: &ClosureBinder,
         capture_clause: CaptureBy,
         closure_id: NodeId,
+        constness: Const,
         movability: Movability,
         decl: &FnDecl,
         body: &Expr,
@@ -927,6 +931,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             fn_decl_span: self.lower_span(fn_decl_span),
             fn_arg_span: Some(self.lower_span(fn_arg_span)),
             movability: generator_option,
+            constness: self.lower_constness(constness),
         });
 
         hir::ExprKind::Closure(c)
@@ -1041,6 +1046,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             fn_decl_span: self.lower_span(fn_decl_span),
             fn_arg_span: Some(self.lower_span(fn_arg_span)),
             movability: None,
+            constness: hir::Constness::NotConst,
         });
         hir::ExprKind::Closure(c)
     }
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index ea30bed5ace..065779d0670 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -1239,7 +1239,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    fn lower_constness(&mut self, c: Const) -> hir::Constness {
+    pub(super) fn lower_constness(&mut self, c: Const) -> hir::Constness {
         match c {
             Const::Yes(_) => hir::Constness::Const,
             Const::No => hir::Constness::NotConst,
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index 3b17f6dd627..b125c6407d0 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -399,6 +399,7 @@ impl<'a> State<'a> {
             ast::ExprKind::Closure(box ast::Closure {
                 binder,
                 capture_clause,
+                constness,
                 asyncness,
                 movability,
                 fn_decl,
@@ -407,6 +408,7 @@ impl<'a> State<'a> {
                 fn_arg_span: _,
             }) => {
                 self.print_closure_binder(binder);
+                self.print_constness(*constness);
                 self.print_movability(*movability);
                 self.print_asyncness(*asyncness);
                 self.print_capture_clause(*capture_clause);
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index 93b3af4ab97..9b16e79d49a 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -533,6 +533,7 @@ impl<'a> ExtCtxt<'a> {
             ast::ExprKind::Closure(Box::new(ast::Closure {
                 binder: ast::ClosureBinder::NotPresent,
                 capture_clause: ast::CaptureBy::Ref,
+                constness: ast::Const::No,
                 asyncness: ast::Async::No,
                 movability: ast::Movability::Movable,
                 fn_decl,
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index bc897ed8112..60f5b79de10 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -938,6 +938,7 @@ pub struct Crate<'hir> {
 pub struct Closure<'hir> {
     pub def_id: LocalDefId,
     pub binder: ClosureBinder,
+    pub constness: Constness,
     pub capture_clause: CaptureBy,
     pub bound_generic_params: &'hir [GenericParam<'hir>],
     pub fn_decl: &'hir FnDecl<'hir>,
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 6c475b659eb..02641b7cf8f 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -742,6 +742,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
             fn_decl_span: _,
             fn_arg_span: _,
             movability: _,
+            constness: _,
         }) => {
             walk_list!(visitor, visit_generic_param, bound_generic_params);
             visitor.visit_fn(FnKind::Closure, fn_decl, body, expression.span, expression.hir_id)
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 3e3af8395a1..f74c551a45b 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -1464,6 +1464,7 @@ impl<'a> State<'a> {
             }
             hir::ExprKind::Closure(&hir::Closure {
                 binder,
+                constness,
                 capture_clause,
                 bound_generic_params,
                 fn_decl,
@@ -1474,6 +1475,7 @@ impl<'a> State<'a> {
                 def_id: _,
             }) => {
                 self.print_closure_binder(binder, bound_generic_params);
+                self.print_constness(constness);
                 self.print_capture_clause(capture_clause);
 
                 self.print_closure_params(fn_decl, body);
@@ -2272,10 +2274,7 @@ impl<'a> State<'a> {
     }
 
     pub fn print_fn_header_info(&mut self, header: hir::FnHeader) {
-        match header.constness {
-            hir::Constness::NotConst => {}
-            hir::Constness::Const => self.word_nbsp("const"),
-        }
+        self.print_constness(header.constness);
 
         match header.asyncness {
             hir::IsAsync::NotAsync => {}
@@ -2292,6 +2291,13 @@ impl<'a> State<'a> {
         self.word("fn")
     }
 
+    pub fn print_constness(&mut self, s: hir::Constness) {
+        match s {
+            hir::Constness::NotConst => {}
+            hir::Constness::Const => self.word_nbsp("const"),
+        }
+    }
+
     pub fn print_unsafety(&mut self, s: hir::Unsafety) {
         match s {
             hir::Unsafety::Normal => {}
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index f5093fb02a8..dd2b03988c3 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1325,7 +1325,10 @@ impl<'a> Parser<'a> {
             self.parse_array_or_repeat_expr(Delimiter::Bracket)
         } else if self.check_path() {
             self.parse_path_start_expr()
-        } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
+        } else if self.check_keyword(kw::Move)
+            || self.check_keyword(kw::Static)
+            || self.check_const_closure()
+        {
             self.parse_closure_expr()
         } else if self.eat_keyword(kw::If) {
             self.parse_if_expr()
@@ -2065,6 +2068,8 @@ impl<'a> Parser<'a> {
             ClosureBinder::NotPresent
         };
 
+        let constness = self.parse_constness(Case::Sensitive);
+
         let movability =
             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
 
@@ -2111,6 +2116,7 @@ impl<'a> Parser<'a> {
             ExprKind::Closure(Box::new(ast::Closure {
                 binder,
                 capture_clause,
+                constness,
                 asyncness,
                 movability,
                 fn_decl,
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 49d31981539..2fd2a4e5154 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -736,6 +736,16 @@ impl<'a> Parser<'a> {
         self.check_or_expected(self.token.can_begin_const_arg(), TokenType::Const)
     }
 
+    fn check_const_closure(&self) -> bool {
+        self.is_keyword_ahead(0, &[kw::Const])
+            && self.look_ahead(1, |t| match &t.kind {
+                token::Ident(kw::Move | kw::Static | kw::Async, _)
+                | token::OrOr
+                | token::BinOp(token::Or) => true,
+                _ => false,
+            })
+    }
+
     fn check_inline_const(&self, dist: usize) -> bool {
         self.is_keyword_ahead(dist, &[kw::Const])
             && self.look_ahead(dist + 1, |t| match &t.kind {
diff --git a/src/tools/rustfmt/src/closures.rs b/src/tools/rustfmt/src/closures.rs
index 244d4427c56..8fd0fcf8f5c 100644
--- a/src/tools/rustfmt/src/closures.rs
+++ b/src/tools/rustfmt/src/closures.rs
@@ -26,6 +26,7 @@ use crate::utils::{last_line_width, left_most_sub_expr, stmt_expr, NodeIdExt};
 
 pub(crate) fn rewrite_closure(
     binder: &ast::ClosureBinder,
+    constness: ast::Const,
     capture: ast::CaptureBy,
     is_async: &ast::Async,
     movability: ast::Movability,
@@ -38,7 +39,7 @@ pub(crate) fn rewrite_closure(
     debug!("rewrite_closure {:?}", body);
 
     let (prefix, extra_offset) = rewrite_closure_fn_decl(
-        binder, capture, is_async, movability, fn_decl, body, span, context, shape,
+        binder, constness, capture, is_async, movability, fn_decl, body, span, context, shape,
     )?;
     // 1 = space between `|...|` and body.
     let body_shape = shape.offset_left(extra_offset)?;
@@ -230,6 +231,7 @@ fn rewrite_closure_block(
 // Return type is (prefix, extra_offset)
 fn rewrite_closure_fn_decl(
     binder: &ast::ClosureBinder,
+    constness: ast::Const,
     capture: ast::CaptureBy,
     asyncness: &ast::Async,
     movability: ast::Movability,
@@ -250,6 +252,12 @@ fn rewrite_closure_fn_decl(
         ast::ClosureBinder::NotPresent => "".to_owned(),
     };
 
+    let const_ = if matches!(constness, ast::Const::Yes(_)) {
+        "const "
+    } else {
+        ""
+    };
+
     let immovable = if movability == ast::Movability::Static {
         "static "
     } else {
@@ -264,7 +272,7 @@ fn rewrite_closure_fn_decl(
     // 4 = "|| {".len(), which is overconservative when the closure consists of
     // a single expression.
     let nested_shape = shape
-        .shrink_left(binder.len() + immovable.len() + is_async.len() + mover.len())?
+        .shrink_left(binder.len() + const_.len() + immovable.len() + is_async.len() + mover.len())?
         .sub_width(4)?;
 
     // 1 = |
@@ -302,7 +310,10 @@ fn rewrite_closure_fn_decl(
         .tactic(tactic)
         .preserve_newline(true);
     let list_str = write_list(&item_vec, &fmt)?;
-    let mut prefix = format!("{}{}{}{}|{}|", binder, immovable, is_async, mover, list_str);
+    let mut prefix = format!(
+        "{}{}{}{}{}|{}|",
+        binder, const_, immovable, is_async, mover, list_str
+    );
 
     if !ret_str.is_empty() {
         if prefix.contains('\n') {
@@ -329,6 +340,7 @@ pub(crate) fn rewrite_last_closure(
     if let ast::ExprKind::Closure(ref closure) = expr.kind {
         let ast::Closure {
             ref binder,
+            constness,
             capture_clause,
             ref asyncness,
             movability,
@@ -349,6 +361,7 @@ pub(crate) fn rewrite_last_closure(
         };
         let (prefix, extra_offset) = rewrite_closure_fn_decl(
             binder,
+            constness,
             capture_clause,
             asyncness,
             movability,
diff --git a/src/tools/rustfmt/src/expr.rs b/src/tools/rustfmt/src/expr.rs
index 414e767690b..868ff045ab7 100644
--- a/src/tools/rustfmt/src/expr.rs
+++ b/src/tools/rustfmt/src/expr.rs
@@ -205,6 +205,7 @@ pub(crate) fn format_expr(
         }
         ast::ExprKind::Closure(ref cl) => closures::rewrite_closure(
             &cl.binder,
+            cl.constness,
             cl.capture_clause,
             &cl.asyncness,
             cl.movability,
diff --git a/tests/ui/parser/recover-quantified-closure.rs b/tests/ui/parser/recover-quantified-closure.rs
index 10af39b7007..df22f5e065c 100644
--- a/tests/ui/parser/recover-quantified-closure.rs
+++ b/tests/ui/parser/recover-quantified-closure.rs
@@ -7,6 +7,6 @@ fn main() {
 enum Foo { Bar }
 fn foo(x: impl Iterator<Item = Foo>) {
     for <Foo>::Bar in x {}
-    //~^ ERROR expected one of `move`, `static`, `|`
+    //~^ ERROR expected one of `const`, `move`, `static`, `|`
     //~^^ ERROR `for<...>` binders for closures are experimental
 }
diff --git a/tests/ui/parser/recover-quantified-closure.stderr b/tests/ui/parser/recover-quantified-closure.stderr
index 39eec80f658..9ec4d2c034d 100644
--- a/tests/ui/parser/recover-quantified-closure.stderr
+++ b/tests/ui/parser/recover-quantified-closure.stderr
@@ -1,8 +1,8 @@
-error: expected one of `move`, `static`, `|`, or `||`, found `::`
+error: expected one of `const`, `move`, `static`, `|`, or `||`, found `::`
   --> $DIR/recover-quantified-closure.rs:9:14
    |
 LL |     for <Foo>::Bar in x {}
-   |              ^^ expected one of `move`, `static`, `|`, or `||`
+   |              ^^ expected one of `const`, `move`, `static`, `|`, or `||`
 
 error[E0658]: `for<...>` binders for closures are experimental
   --> $DIR/recover-quantified-closure.rs:2:5