Add catch expr to AST and disallow catch as a struct name

src/librustc/hir/lowering.rs

@@ -84,6 +84,7 @@ pub struct LoweringContext<'a> {
     trait_impls: BTreeMap<DefId, Vec<NodeId>>,
     trait_default_impl: BTreeMap<DefId, NodeId>,
 
+    catch_scopes: Vec<NodeId>,
     loop_scopes: Vec<NodeId>,
     is_in_loop_condition: bool,
 
@@ -123,6 +124,7 @@ pub fn lower_crate(sess: &Session,
         trait_impls: BTreeMap::new(),
         trait_default_impl: BTreeMap::new(),
         exported_macros: Vec::new(),
+        catch_scopes: Vec::new(),
         loop_scopes: Vec::new(),
         is_in_loop_condition: false,
         type_def_lifetime_params: DefIdMap(),
@@ -261,6 +263,21 @@ impl<'a> LoweringContext<'a> {
         span
     }
 
+    fn with_catch_scope<T, F>(&mut self, catch_id: NodeId, f: F) -> T
+        where F: FnOnce(&mut LoweringContext) -> T
+    {
+        let len = self.catch_scopes.len();
+        self.catch_scopes.push(catch_id);
+
+        let result = f(self);
+        assert_eq!(len + 1, self.catch_scopes.len(),
+            "catch scopes should be added and removed in stack order");
+
+        self.catch_scopes.pop().unwrap();
+
+        result
+    }
+
     fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
         where F: FnOnce(&mut LoweringContext) -> T
     {
@@ -295,15 +312,17 @@ impl<'a> LoweringContext<'a> {
         result
     }
 
-    fn with_new_loop_scopes<T, F>(&mut self, f: F) -> T
+    fn with_new_scopes<T, F>(&mut self, f: F) -> T
         where F: FnOnce(&mut LoweringContext) -> T
     {
         let was_in_loop_condition = self.is_in_loop_condition;
         self.is_in_loop_condition = false;
 
+        let catch_scopes = mem::replace(&mut self.catch_scopes, Vec::new());
         let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
         let result = f(self);
-        mem::replace(&mut self.loop_scopes, loop_scopes);
+        self.catch_scopes = catch_scopes;
+        self.loop_scopes = loop_scopes;
 
         self.is_in_loop_condition = was_in_loop_condition;
 
@@ -1065,7 +1084,7 @@ impl<'a> LoweringContext<'a> {
                                self.record_body(value, None))
             }
             ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
-                self.with_new_loop_scopes(|this| {
+                self.with_new_scopes(|this| {
                     let body = this.lower_block(body);
                     let body = this.expr_block(body, ThinVec::new());
                     let body_id = this.record_body(body, Some(decl));
@@ -1665,13 +1684,17 @@ impl<'a> LoweringContext<'a> {
                                       this.lower_opt_sp_ident(opt_ident),
                                       hir::LoopSource::Loop))
                 }
+                ExprKind::Catch(ref body) => {
+                    // FIXME(cramertj): Add catch to HIR
+                    self.with_catch_scope(e.id, |this| hir::ExprBlock(this.lower_block(body)))
+                }
                 ExprKind::Match(ref expr, ref arms) => {
                     hir::ExprMatch(P(self.lower_expr(expr)),
                                    arms.iter().map(|x| self.lower_arm(x)).collect(),
                                    hir::MatchSource::Normal)
                 }
                 ExprKind::Closure(capture_clause, ref decl, ref body, fn_decl_span) => {
-                    self.with_new_loop_scopes(|this| {
+                    self.with_new_scopes(|this| {
                         this.with_parent_def(e.id, |this| {
                             let expr = this.lower_expr(body);
                             hir::ExprClosure(this.lower_capture_clause(capture_clause),
@@ -2069,6 +2092,12 @@ impl<'a> LoweringContext<'a> {
                     //     Err(err) => #[allow(unreachable_code)]
                     //                 return Carrier::from_error(From::from(err)),
                     // }
+
+                    // FIXME(cramertj): implement breaking to catch
+                    if !self.catch_scopes.is_empty() {
+                        bug!("`?` in catch scopes is unimplemented")
+                    }
+
                     let unstable_span = self.allow_internal_unstable("?", e.span);
 
                     // Carrier::translate(<expr>)

src/libsyntax/ast.rs

@@ -935,6 +935,8 @@ pub enum ExprKind {
     Closure(CaptureBy, P<FnDecl>, P<Expr>, Span),
     /// A block (`{ ... }`)
     Block(P<Block>),
+    /// A catch block (`catch { ... }`)
+    Catch(P<Block>),
 
     /// An assignment (`a = foo()`)
     Assign(P<Expr>, P<Expr>),

src/libsyntax/feature_gate.rs

@@ -339,6 +339,9 @@ declare_features! (
 
     // `extern "x86-interrupt" fn()`
     (active, abi_x86_interrupt, "1.17.0", Some(40180)),
+
+    // Allows the `catch {...}` expression
+    (active, catch_expr, "1.17.0", Some(31436)),
 );
 
 declare_features! (
@@ -1287,6 +1290,9 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     }
                 }
             }
+            ast::ExprKind::Catch(_) => {
+                gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
+            }
             _ => {}
         }
         visit::walk_expr(self, e);

src/libsyntax/fold.rs

@@ -1268,6 +1268,7 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mu
                 };
             }
             ExprKind::Try(ex) => ExprKind::Try(folder.fold_expr(ex)),
+            ExprKind::Catch(body) => ExprKind::Catch(folder.fold_block(body)),
         },
         id: folder.new_id(id),
         span: folder.new_span(span),

src/libsyntax/parse/parser.rs

@@ -602,6 +602,12 @@ impl<'a> Parser<'a> {
         }
     }
 
+    pub fn error_if_typename_is_catch(&mut self, ident: ast::Ident) {
+        if ident.name == keywords::Catch.name() {
+            self.span_err(self.span, "cannot use `catch` as the name of a type");
+        }
+    }
+
     /// Check if the next token is `tok`, and return `true` if so.
     ///
     /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
@@ -2273,6 +2279,11 @@ impl<'a> Parser<'a> {
                         BlockCheckMode::Unsafe(ast::UserProvided),
                         attrs);
                 }
+                if self.is_catch_expr() {
+                    assert!(self.eat_keyword(keywords::Catch));
+                    let lo = self.prev_span.lo;
+                    return self.parse_catch_expr(lo, attrs);
+                }
                 if self.eat_keyword(keywords::Return) {
                     if self.token.can_begin_expr() {
                         let e = self.parse_expr()?;
@@ -3092,6 +3103,16 @@ impl<'a> Parser<'a> {
         Ok(self.mk_expr(span_lo, hi, ExprKind::Loop(body, opt_ident), attrs))
     }
 
+    /// Parse a `catch {...}` expression (`catch` token already eaten)
+    pub fn parse_catch_expr(&mut self, span_lo: BytePos, mut attrs: ThinVec<Attribute>)
+        -> PResult<'a, P<Expr>>
+    {
+        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+        let hi = body.span.hi;
+        Ok(self.mk_expr(span_lo, hi, ExprKind::Catch(body), attrs))
+    }
+
     // `match` token already eaten
     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
         let match_span = self.prev_span;
@@ -3699,6 +3720,14 @@ impl<'a> Parser<'a> {
         })
     }
 
+    fn is_catch_expr(&mut self) -> bool {
+        self.token.is_keyword(keywords::Catch) &&
+        self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
+
+        // prevent `while catch {} {}`, `if catch {} {} else {}`, etc.
+        !self.restrictions.contains(Restrictions::RESTRICTION_NO_STRUCT_LITERAL)
+    }
+
     fn is_union_item(&self) -> bool {
         self.token.is_keyword(keywords::Union) &&
         self.look_ahead(1, |t| t.is_ident() && !t.is_any_keyword())
@@ -4875,6 +4904,8 @@ impl<'a> Parser<'a> {
     /// Parse struct Foo { ... }
     fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
         let class_name = self.parse_ident()?;
+        self.error_if_typename_is_catch(class_name);
+
         let mut generics = self.parse_generics()?;
 
         // There is a special case worth noting here, as reported in issue #17904.
@@ -4924,6 +4955,8 @@ impl<'a> Parser<'a> {
     /// Parse union Foo { ... }
     fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
         let class_name = self.parse_ident()?;
+        self.error_if_typename_is_catch(class_name);
+
         let mut generics = self.parse_generics()?;
 
         let vdata = if self.token.is_keyword(keywords::Where) {
@@ -5440,6 +5473,7 @@ impl<'a> Parser<'a> {
             let struct_def;
             let mut disr_expr = None;
             let ident = self.parse_ident()?;
+            self.error_if_typename_is_catch(ident);
             if self.check(&token::OpenDelim(token::Brace)) {
                 // Parse a struct variant.
                 all_nullary = false;
@@ -5481,6 +5515,7 @@ impl<'a> Parser<'a> {
     /// Parse an "enum" declaration
     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
         let id = self.parse_ident()?;
+        self.error_if_typename_is_catch(id);
         let mut generics = self.parse_generics()?;
         generics.where_clause = self.parse_where_clause()?;
         self.expect(&token::OpenDelim(token::Brace))?;

src/libsyntax/print/pprust.rs

@@ -2279,6 +2279,11 @@ impl<'a> State<'a> {
                 self.print_expr(e)?;
                 word(&mut self.s, "?")?
             }
+            ast::ExprKind::Catch(ref blk) => {
+                self.head("catch")?;
+                space(&mut self.s)?;
+                self.print_block_with_attrs(&blk, attrs)?
+            }
         }
         self.ann.post(self, NodeExpr(expr))?;
         self.end()

src/libsyntax/symbol.rs

@@ -221,9 +221,10 @@ declare_keywords! {
     (53, Default,        "default")
     (54, StaticLifetime, "'static")
     (55, Union,          "union")
+    (56, Catch,          "catch")
 
     // A virtual keyword that resolves to the crate root when used in a lexical scope.
-    (56, CrateRoot, "{{root}}")
+    (57, CrateRoot, "{{root}}")
 }
 
 // If an interner exists in TLS, return it. Otherwise, prepare a fresh one.

src/libsyntax/visit.rs

@@ -779,6 +779,9 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::Try(ref subexpression) => {
             visitor.visit_expr(subexpression)
         }
+        ExprKind::Catch(ref body) => {
+            visitor.visit_block(body)
+        }
     }
 
     visitor.visit_expr_post(expression)

src/test/compile-fail/catch-empty-struct-name.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(non_camel_case_types)]
+#![allow(dead_code)]
+#![feature(catch_expr)]
+
+struct catch; //~ ERROR cannot use `catch` as the name of a type

src/test/compile-fail/catch-enum-variant.rs

@@ -0,0 +1,17 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(non_camel_case_types)]
+#![allow(dead_code)]
+#![feature(catch_expr)]
+
+enum Enum {
+    catch {} //~ ERROR cannot use `catch` as the name of a type
+}

src/test/compile-fail/catch-struct-name.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(non_camel_case_types)]
+#![allow(dead_code)]
+#![feature(catch_expr)]
+
+struct catch {} //~ ERROR cannot use `catch` as the name of a type

src/test/compile-fail/catch-tuple-struct-name.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(non_camel_case_types)]
+#![allow(dead_code)]
+#![feature(catch_expr)]
+
+struct catch(); //~ ERROR cannot use `catch` as the name of a type

src/test/compile-fail/feature-gate-catch_expr.rs

@@ -0,0 +1,17 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub fn main() {
+    let catch_result = catch { //~ ERROR `catch` expression is experimental
+        let x = 5;
+        x
+    };
+    assert_eq!(catch_result, 5);
+}

src/test/run-pass/catch-expr.rs

@@ -0,0 +1,30 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(catch_expr)]
+
+pub fn main() {
+    let catch_result = catch {
+        let x = 5;
+        x
+    };
+    assert_eq!(catch_result, 5);
+
+    let mut catch = true;
+    while catch { catch = false; }
+    assert_eq!(catch, false);
+
+    catch = if catch { false } else { true };
+    assert_eq!(catch, true);
+
+    match catch {
+        _ => {}
+    };
+}