Auto merge of #52602 - scottmcm:tryblock-expr, r=nikomatsakis

Implement try block expressions

I noticed that `try` wasn't a keyword yet in Rust 2018, so...

~~Fix​es https://github.com/rust-lang/rust/issues/52604~~ That was fixed by PR https://github.com/rust-lang/rust/pull/53135
cc https://github.com/rust-lang/rust/issues/31436 https://github.com/rust-lang/rust/issues/50412

src/doc/unstable-book/src/language-features/try-blocks.md

@@ -1,4 +1,4 @@
-# `catch_expr`
+# `try_blocks`
 
 The tracking issue for this feature is: [#31436]
 
@@ -6,22 +6,24 @@ The tracking issue for this feature is: [#31436]
 
 ------------------------
 
-The `catch_expr` feature adds support for a `catch` expression. The `catch`
-expression creates a new scope one can use the `?` operator in.
+The `try_blocks` feature adds support for `try` blocks. A `try`
+block creates a new scope one can use the `?` operator in.
 
-```rust
-#![feature(catch_expr)]
+```rust,ignore
+// This code needs the 2018 edition
+
+#![feature(try_blocks)]
 
 use std::num::ParseIntError;
 
-let result: Result<i32, ParseIntError> = do catch {
+let result: Result<i32, ParseIntError> = try {
     "1".parse::<i32>()?
         + "2".parse::<i32>()?
         + "3".parse::<i32>()?
 };
 assert_eq!(result, Ok(6));
 
-let result: Result<i32, ParseIntError> = do catch {
+let result: Result<i32, ParseIntError> = try {
     "1".parse::<i32>()?
         + "foo".parse::<i32>()?
         + "3".parse::<i32>()?

src/librustc/hir/lowering.rs

@@ -3613,10 +3613,10 @@ impl<'a> LoweringContext<'a> {
                     hir::LoopSource::Loop,
                 )
             }),
-            ExprKind::Catch(ref body) => {
+            ExprKind::TryBlock(ref body) => {
                 self.with_catch_scope(body.id, |this| {
                     let unstable_span =
-                        this.allow_internal_unstable(CompilerDesugaringKind::Catch, body.span);
+                        this.allow_internal_unstable(CompilerDesugaringKind::TryBlock, body.span);
                     let mut block = this.lower_block(body, true).into_inner();
                     let tail = block.expr.take().map_or_else(
                         || {

src/librustc/ich/impls_syntax.rs

@@ -412,7 +412,7 @@ impl_stable_hash_for!(enum ::syntax_pos::hygiene::CompilerDesugaringKind {
     QuestionMark,
     ExistentialReturnType,
     ForLoop,
-    Catch
+    TryBlock
 });
 
 impl_stable_hash_for!(enum ::syntax_pos::FileName {

src/librustc/lib.rs

@@ -65,7 +65,6 @@
 #![feature(trace_macros)]
 #![feature(trusted_len)]
 #![feature(vec_remove_item)]
-#![feature(catch_expr)]
 #![feature(step_trait)]
 #![feature(integer_atomics)]
 #![feature(test)]

src/librustc_mir/borrow_check/nll/mod.rs

@@ -312,14 +312,14 @@ fn dump_mir_results<'a, 'gcx, 'tcx>(
     );
 
     // Also dump the inference graph constraints as a graphviz file.
-    let _: io::Result<()> = do catch {
+    let _: io::Result<()> = try_block! {
         let mut file =
             pretty::create_dump_file(infcx.tcx, "regioncx.all.dot", None, "nll", &0, source)?;
         regioncx.dump_graphviz_raw_constraints(&mut file)?;
     };
 
     // Also dump the inference graph constraints as a graphviz file.
-    let _: io::Result<()> = do catch {
+    let _: io::Result<()> = try_block! {
         let mut file =
             pretty::create_dump_file(infcx.tcx, "regioncx.scc.dot", None, "nll", &0, source)?;
         regioncx.dump_graphviz_scc_constraints(&mut file)?;

src/librustc_mir/lib.rs

@@ -21,7 +21,6 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(slice_sort_by_cached_key)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(catch_expr)]
 #![feature(crate_visibility_modifier)]
 #![feature(const_fn)]
 #![feature(core_intrinsics)]
@@ -63,6 +62,14 @@ extern crate rustc_apfloat;
 extern crate byteorder;
 extern crate core;
 
+// Once we can use edition 2018 in the compiler,
+// replace this with real try blocks.
+macro_rules! try_block {
+    ($($inside:tt)*) => (
+        (||{ ::std::ops::Try::from_ok({ $($inside)* }) })()
+    )
+}
+
 mod diagnostics;
 
 mod borrow_check;

src/librustc_mir/util/pretty.rs

@@ -140,7 +140,7 @@ fn dump_matched_mir_node<'a, 'gcx, 'tcx, F>(
 ) where
     F: FnMut(PassWhere, &mut dyn Write) -> io::Result<()>,
 {
-    let _: io::Result<()> = do catch {
+    let _: io::Result<()> = try_block! {
         let mut file = create_dump_file(tcx, "mir", pass_num, pass_name, disambiguator, source)?;
         writeln!(file, "// MIR for `{}`", node_path)?;
         writeln!(file, "// source = {:?}", source)?;
@@ -156,7 +156,7 @@ fn dump_matched_mir_node<'a, 'gcx, 'tcx, F>(
     };
 
     if tcx.sess.opts.debugging_opts.dump_mir_graphviz {
-        let _: io::Result<()> = do catch {
+        let _: io::Result<()> = try_block! {
             let mut file =
                 create_dump_file(tcx, "dot", pass_num, pass_name, disambiguator, source)?;
             write_mir_fn_graphviz(tcx, source.def_id, mir, &mut file)?;

src/librustc_typeck/check/mod.rs

@@ -4471,7 +4471,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // In some cases, blocks have just one exit, but other blocks
         // can be targeted by multiple breaks. This can happen both
         // with labeled blocks as well as when we desugar
-        // a `do catch { ... }` expression.
+        // a `try { ... }` expression.
         //
         // Example 1:
         //

src/libsyntax/ast.rs

@@ -987,7 +987,7 @@ impl Expr {
             ExprKind::Match(..) => ExprPrecedence::Match,
             ExprKind::Closure(..) => ExprPrecedence::Closure,
             ExprKind::Block(..) => ExprPrecedence::Block,
-            ExprKind::Catch(..) => ExprPrecedence::Catch,
+            ExprKind::TryBlock(..) => ExprPrecedence::TryBlock,
             ExprKind::Async(..) => ExprPrecedence::Async,
             ExprKind::Assign(..) => ExprPrecedence::Assign,
             ExprKind::AssignOp(..) => ExprPrecedence::AssignOp,
@@ -1108,8 +1108,8 @@ pub enum ExprKind {
     /// created during lowering cannot be made the parent of any other
     /// preexisting defs.
     Async(CaptureBy, NodeId, P<Block>),
-    /// A catch block (`catch { ... }`)
-    Catch(P<Block>),
+    /// A try block (`try { ... }`)
+    TryBlock(P<Block>),
 
     /// An assignment (`a = foo()`)
     Assign(P<Expr>, P<Expr>),

src/libsyntax/feature_gate.rs

@@ -333,8 +333,8 @@ declare_features! (
     // `extern "x86-interrupt" fn()`
     (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
 
-    // Allows the `catch {...}` expression
-    (active, catch_expr, "1.17.0", Some(31436), None),
+    // Allows the `try {...}` expression
+    (active, try_blocks, "1.29.0", Some(31436), None),
 
     // Used to preserve symbols (see llvm.used)
     (active, used, "1.18.0", Some(40289), None),
@@ -1734,8 +1734,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                   e.span,
                                   "yield syntax is experimental");
             }
-            ast::ExprKind::Catch(_) => {
-                gate_feature_post!(&self, catch_expr, e.span, "`catch` expression is experimental");
+            ast::ExprKind::TryBlock(_) => {
+                gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
             }
             ast::ExprKind::IfLet(ref pats, ..) | ast::ExprKind::WhileLet(ref pats, ..) => {
                 if pats.len() > 1 {

src/libsyntax/fold.rs

@@ -1351,7 +1351,7 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mu
             }
             ExprKind::Yield(ex) => ExprKind::Yield(ex.map(|x| folder.fold_expr(x))),
             ExprKind::Try(ex) => ExprKind::Try(folder.fold_expr(ex)),
-            ExprKind::Catch(body) => ExprKind::Catch(folder.fold_block(body)),
+            ExprKind::TryBlock(body) => ExprKind::TryBlock(folder.fold_block(body)),
         },
         id: folder.new_id(id),
         span: folder.new_span(span),

src/libsyntax/lib.rs

@@ -26,8 +26,8 @@
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(str_escape)]
+#![feature(try_trait)]
 #![feature(unicode_internals)]
-#![feature(catch_expr)]
 
 #![recursion_limit="256"]
 

src/libsyntax/parse/classify.rs

@@ -31,7 +31,7 @@ pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
         ast::ExprKind::WhileLet(..) |
         ast::ExprKind::Loop(..) |
         ast::ExprKind::ForLoop(..) |
-        ast::ExprKind::Catch(..) => false,
+        ast::ExprKind::TryBlock(..) => false,
         _ => true,
     }
 }

src/libsyntax/parse/parser.rs

@@ -1757,9 +1757,17 @@ impl<'a> Parser<'a> {
 
             let parser_snapshot_before_pat = self.clone();
 
+            // Once we can use edition 2018 in the compiler,
+            // replace this with real try blocks.
+            macro_rules! try_block {
+                ($($inside:tt)*) => (
+                    (||{ ::std::ops::Try::from_ok({ $($inside)* }) })()
+                )
+            }
+
             // We're going to try parsing the argument as a pattern (even though it's not
             // allowed). This way we can provide better errors to the user.
-            let pat_arg: PResult<'a, _> = do catch {
+            let pat_arg: PResult<'a, _> = try_block! {
                 let pat = self.parse_pat()?;
                 self.expect(&token::Colon)?;
                 (pat, self.parse_ty()?)
@@ -2387,11 +2395,15 @@ impl<'a> Parser<'a> {
                         BlockCheckMode::Unsafe(ast::UserProvided),
                         attrs);
                 }
-                if self.is_catch_expr() {
+                if self.is_do_catch_block() {
+                    let mut db = self.fatal("found removed `do catch` syntax");
+                    db.help("Following RFC #2388, the new non-placeholder syntax is `try`");
+                    return Err(db);
+                }
+                if self.is_try_block() {
                     let lo = self.span;
-                    assert!(self.eat_keyword(keywords::Do));
-                    assert!(self.eat_keyword(keywords::Catch));
-                    return self.parse_catch_expr(lo, attrs);
+                    assert!(self.eat_keyword(keywords::Try));
+                    return self.parse_try_block(lo, attrs);
                 }
                 if self.eat_keyword(keywords::Return) {
                     if self.token.can_begin_expr() {
@@ -3453,13 +3465,13 @@ impl<'a> Parser<'a> {
             ExprKind::Async(capture_clause, ast::DUMMY_NODE_ID, body), attrs))
     }
 
-    /// Parse a `do catch {...}` expression (`do catch` token already eaten)
-    fn parse_catch_expr(&mut self, span_lo: Span, mut attrs: ThinVec<Attribute>)
+    /// Parse a `try {...}` expression (`try` token already eaten)
+    fn parse_try_block(&mut self, span_lo: Span, mut attrs: ThinVec<Attribute>)
         -> PResult<'a, P<Expr>>
     {
         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
         attrs.extend(iattrs);
-        Ok(self.mk_expr(span_lo.to(body.span), ExprKind::Catch(body), attrs))
+        Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
     }
 
     // `match` token already eaten
@@ -4408,12 +4420,20 @@ impl<'a> Parser<'a> {
         )
     }
 
-    fn is_catch_expr(&mut self) -> bool {
+    fn is_do_catch_block(&mut self) -> bool {
         self.token.is_keyword(keywords::Do) &&
         self.look_ahead(1, |t| t.is_keyword(keywords::Catch)) &&
         self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
+        !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+    }
 
-        // prevent `while catch {} {}`, `if catch {} {} else {}`, etc.
+    fn is_try_block(&mut self) -> bool {
+        self.token.is_keyword(keywords::Try) &&
+        self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
+
+        self.span.edition() >= Edition::Edition2018 &&
+
+        // prevent `while try {} {}`, `if try {} {} else {}`, etc.
         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
     }
 

src/libsyntax/print/pprust.rs

@@ -2379,8 +2379,8 @@ impl<'a> State<'a> {
                 self.print_expr_maybe_paren(e, parser::PREC_POSTFIX)?;
                 self.s.word("?")?
             }
-            ast::ExprKind::Catch(ref blk) => {
-                self.head("do catch")?;
+            ast::ExprKind::TryBlock(ref blk) => {
+                self.head("try")?;
                 self.s.space()?;
                 self.print_block_with_attrs(blk, attrs)?
             }

src/libsyntax/util/parser.rs

@@ -273,7 +273,7 @@ pub enum ExprPrecedence {
     Loop,
     Match,
     Block,
-    Catch,
+    TryBlock,
     Struct,
     Async,
 }
@@ -332,7 +332,7 @@ impl ExprPrecedence {
             ExprPrecedence::Loop |
             ExprPrecedence::Match |
             ExprPrecedence::Block |
-            ExprPrecedence::Catch |
+            ExprPrecedence::TryBlock |
             ExprPrecedence::Async |
             ExprPrecedence::Struct => PREC_PAREN,
         }

src/libsyntax/visit.rs

@@ -809,7 +809,7 @@ 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) => {
+        ExprKind::TryBlock(ref body) => {
             visitor.visit_block(body)
         }
     }

src/libsyntax_pos/hygiene.rs

@@ -595,7 +595,7 @@ impl ExpnFormat {
 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 pub enum CompilerDesugaringKind {
     QuestionMark,
-    Catch,
+    TryBlock,
     /// Desugaring of an `impl Trait` in return type position
     /// to an `existential type Foo: Trait;` + replacing the
     /// `impl Trait` with `Foo`.
@@ -609,7 +609,7 @@ impl CompilerDesugaringKind {
         Symbol::intern(match self {
             CompilerDesugaringKind::Async => "async",
             CompilerDesugaringKind::QuestionMark => "?",
-            CompilerDesugaringKind::Catch => "do catch",
+            CompilerDesugaringKind::TryBlock => "try block",
             CompilerDesugaringKind::ExistentialReturnType => "existential type",
             CompilerDesugaringKind::ForLoop => "for loop",
         })

src/libsyntax_pos/symbol.rs

@@ -415,23 +415,25 @@ declare_keywords! {
 
     // Edition-specific keywords reserved for future use.
     (51, Async,              "async") // >= 2018 Edition Only
+    (52, Try,                "try") // >= 2018 Edition Only
 
     // Special lifetime names
-    (52, UnderscoreLifetime, "'_")
-    (53, StaticLifetime,     "'static")
+    (53, UnderscoreLifetime, "'_")
+    (54, StaticLifetime,     "'static")
 
     // Weak keywords, have special meaning only in specific contexts.
-    (54, Auto,               "auto")
-    (55, Catch,              "catch")
-    (56, Default,            "default")
-    (57, Dyn,                "dyn")
-    (58, Union,              "union")
-    (59, Existential,        "existential")
+    (55, Auto,               "auto")
+    (56, Catch,              "catch")
+    (57, Default,            "default")
+    (58, Dyn,                "dyn")
+    (59, Union,              "union")
+    (60, Existential,        "existential")
 }
 
 impl Symbol {
     fn is_unused_keyword_2018(self) -> bool {
-        self == keywords::Async.name()
+        self >= keywords::Async.name() &&
+        self <= keywords::Try.name()
     }
 }
 

src/test/parse-fail/do-catch-suggests-try.rs

@@ -0,0 +1,17 @@
+// Copyright 2018 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.
+
+// compile-flags: -Z parse-only
+
+fn main() {
+    let _: Option<()> = do catch {};
+    //~^ ERROR found removed `do catch` syntax
+    //~^^ HELP Following RFC #2388, the new non-placeholder syntax is `try`
+}

src/test/parse-fail/keyword-try-as-identifier-edition2018.rs

@@ -0,0 +1,15 @@
+// Copyright 2018 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.
+
+// compile-flags: -Z parse-only --edition 2018
+
+fn main() {
+    let try = "foo"; //~ error: expected pattern, found reserved keyword `try`
+}

src/test/run-pass/issue-45124.rs

@@ -8,12 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 fn main() {
     let mut a = 0;
     let () = {
-        let _: Result<(), ()> = do catch {
+        let _: Result<(), ()> = try {
             let _ = Err(())?;
             return
         };

src/test/run-pass/try-block.rs

@@ -8,12 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 struct catch {}
 
 pub fn main() {
-    let catch_result: Option<_> = do catch {
+    let catch_result: Option<_> = try {
         let x = 5;
         x
     };
@@ -30,20 +32,20 @@ pub fn main() {
         _ => {}
     };
 
-    let catch_err: Result<_, i32> = do catch {
+    let catch_err: Result<_, i32> = try {
         Err(22)?;
         1
     };
     assert_eq!(catch_err, Err(22));
 
-    let catch_okay: Result<i32, i32> = do catch {
+    let catch_okay: Result<i32, i32> = try {
         if false { Err(25)?; }
         Ok::<(), i32>(())?;
         28
     };
     assert_eq!(catch_okay, Ok(28));
 
-    let catch_from_loop: Result<i32, i32> = do catch {
+    let catch_from_loop: Result<i32, i32> = try {
         for i in 0..10 {
             if i < 5 { Ok::<i32, i32>(i)?; } else { Err(i)?; }
         }
@@ -52,28 +54,28 @@ pub fn main() {
     assert_eq!(catch_from_loop, Err(5));
 
     let cfg_init;
-    let _res: Result<(), ()> = do catch {
+    let _res: Result<(), ()> = try {
         cfg_init = 5;
     };
     assert_eq!(cfg_init, 5);
 
     let cfg_init_2;
-    let _res: Result<(), ()> = do catch {
+    let _res: Result<(), ()> = try {
         cfg_init_2 = 6;
         Err(())?;
     };
     assert_eq!(cfg_init_2, 6);
 
     let my_string = "test".to_string();
-    let res: Result<&str, ()> = do catch {
+    let res: Result<&str, ()> = try {
         // Unfortunately, deref doesn't fire here (#49356)
         &my_string[..]
     };
     assert_eq!(res, Ok("test"));
 
-    let my_opt: Option<_> = do catch { () };
+    let my_opt: Option<_> = try { () };
     assert_eq!(my_opt, Some(()));
 
-    let my_opt: Option<_> = do catch { };
+    let my_opt: Option<_> = try { };
     assert_eq!(my_opt, Some(()));
 }

src/test/run-pass/try-is-identifier-edition2015.rs

@@ -0,0 +1,18 @@
+// Copyright 2018 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.
+
+// compile-flags: --edition 2015
+
+fn main() {
+    let try = 2;
+    struct try { try: u32 };
+    let try: try = try { try };
+    assert_eq!(try.try, 2);
+}

src/test/ui/catch/catch-bad-lifetime.stderr

@@ -1,44 +0,0 @@
-error[E0597]: `my_string` does not live long enough
-  --> $DIR/catch-bad-lifetime.rs:20:35
-   |
-LL |             let my_str: & str = & my_string;
-   |                                   ^^^^^^^^^ borrowed value does not live long enough
-...
-LL |         };
-   |         - `my_string` dropped here while still borrowed
-LL |     }
-   |     - borrowed value needs to live until here
-
-error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-bad-lifetime.rs:33:13
-   |
-LL |         let k = &mut i;
-   |                      - borrow of `i` occurs here
-...
-LL |             i = 10; //~ ERROR cannot assign to `i` because it is borrowed
-   |             ^^^^^^ assignment to borrowed `i` occurs here
-
-error[E0382]: use of moved value: `k`
-  --> $DIR/catch-bad-lifetime.rs:35:26
-   |
-LL |             Err(k) ?;
-   |                 - value moved here
-...
-LL |         ::std::mem::drop(k); //~ ERROR use of moved value: `k`
-   |                          ^ value used here after move
-   |
-   = note: move occurs because `k` has type `&mut i32`, which does not implement the `Copy` trait
-
-error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-bad-lifetime.rs:36:9
-   |
-LL |         let k = &mut i;
-   |                      - borrow of `i` occurs here
-...
-LL |         i = 40; //~ ERROR cannot assign to `i` because it is borrowed
-   |         ^^^^^^ assignment to borrowed `i` occurs here
-
-error: aborting due to 4 previous errors
-
-Some errors occurred: E0382, E0506, E0597.
-For more information about an error, try `rustc --explain E0382`.

src/test/ui/catch/catch-in-match.stderr

@@ -1,8 +0,0 @@
-error: expected expression, found reserved keyword `do`
-  --> $DIR/catch-in-match.rs:14:11
-   |
-LL |     match do catch { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `do`
-   |           ^^ expected expression
-
-error: aborting due to previous error
-

src/test/ui/catch/catch-in-while.stderr

@@ -1,8 +0,0 @@
-error: expected expression, found reserved keyword `do`
-  --> $DIR/catch-in-while.rs:14:11
-   |
-LL |     while do catch { false } {} //~ ERROR expected expression, found reserved keyword `do`
-   |           ^^ expected expression
-
-error: aborting due to previous error
-

src/test/ui/catch/catch-maybe-bad-lifetime.nll.stderr

@@ -1,14 +0,0 @@
-error[E0382]: borrow of moved value: `x`
-  --> $DIR/catch-maybe-bad-lifetime.rs:33:24
-   |
-LL |             ::std::mem::drop(x);
-   |                              - value moved here
-LL |         };
-LL |         println!("{}", x); //~ ERROR use of moved value: `x`
-   |                        ^ value borrowed here after move
-   |
-   = note: move occurs because `x` has type `std::string::String`, which does not implement the `Copy` trait
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0382`.

src/test/ui/catch/catch-opt-init.stderr

@@ -1,9 +0,0 @@
-error[E0381]: use of possibly uninitialized variable: `cfg_res`
-  --> $DIR/catch-opt-init.rs:23:16
-   |
-LL |     assert_eq!(cfg_res, 5); //~ ERROR use of possibly uninitialized variable
-   |                ^^^^^^^ use of possibly uninitialized `cfg_res`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0381`.

src/test/ui/feature-gates/feature-gate-catch_expr.stderr

@@ -1,15 +0,0 @@
-error[E0658]: `catch` expression is experimental (see issue #31436)
-  --> $DIR/feature-gate-catch_expr.rs:12:24
-   |
-LL |       let catch_result = do catch { //~ ERROR `catch` expression is experimental
-   |  ________________________^
-LL | |         let x = 5;
-LL | |         x
-LL | |     };
-   | |_____^
-   |
-   = help: add #![feature(catch_expr)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-try_blocks.rs

@@ -8,10 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: --edition 2018
+
 pub fn main() {
-    let catch_result = do catch { //~ ERROR `catch` expression is experimental
+    let try_result: Option<_> = try { //~ ERROR `try` expression is experimental
         let x = 5;
         x
     };
-    assert_eq!(catch_result, 5);
+    assert_eq!(try_result, Some(5));
 }

src/test/ui/feature-gates/feature-gate-try_blocks.stderr

@@ -0,0 +1,15 @@
+error[E0658]: `try` expression is experimental (see issue #31436)
+  --> $DIR/feature-gate-try_blocks.rs:14:33
+   |
+LL |       let try_result: Option<_> = try { //~ ERROR `try` expression is experimental
+   |  _________________________________^
+LL | |         let x = 5;
+LL | |         x
+LL | |     };
+   | |_____^
+   |
+   = help: add #![feature(try_blocks)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/try-block/try-block-bad-lifetime.rs

@@ -8,27 +8,33 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
 
-// This test checks that borrows made and returned inside catch blocks are properly constrained
+#![feature(try_blocks)]
+
+#![inline(never)]
+fn do_something_with<T>(_x: T) {}
+
+// This test checks that borrows made and returned inside try blocks are properly constrained
 pub fn main() {
     {
-        // Test that borrows returned from a catch block must be valid for the lifetime of the
+        // Test that borrows returned from a try block must be valid for the lifetime of the
         // result variable
-        let _result: Result<(), &str> = do catch {
+        let result: Result<(), &str> = try {
             let my_string = String::from("");
             let my_str: & str = & my_string;
             //~^ ERROR `my_string` does not live long enough
             Err(my_str) ?;
             Err("") ?;
         };
+        do_something_with(result);
     }
 
     {
-        // Test that borrows returned from catch blocks freeze their referent
+        // Test that borrows returned from try blocks freeze their referent
         let mut i = 5;
         let k = &mut i;
-        let mut j: Result<(), &mut i32> = do catch {
+        let mut j: Result<(), &mut i32> = try {
             Err(k) ?;
             i = 10; //~ ERROR cannot assign to `i` because it is borrowed
         };

src/test/ui/try-block/try-block-bad-lifetime.stderr

@@ -1,5 +1,16 @@
+error[E0597]: `my_string` does not live long enough
+  --> $DIR/try-block-bad-lifetime.rs:25:33
+   |
+LL |             let my_str: & str = & my_string;
+   |                                 ^^^^^^^^^^^ borrowed value does not live long enough
+...
+LL |         };
+   |         - `my_string` dropped here while still borrowed
+LL |         do_something_with(result);
+   |                           ------ borrow later used here
+
 error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-bad-lifetime.rs:33:13
+  --> $DIR/try-block-bad-lifetime.rs:39:13
    |
 LL |         let k = &mut i;
    |                 ------ borrow of `i` occurs here
@@ -11,7 +22,7 @@ LL |         ::std::mem::drop(k); //~ ERROR use of moved value: `k`
    |                          - borrow later used here
 
 error[E0382]: use of moved value: `k`
-  --> $DIR/catch-bad-lifetime.rs:35:26
+  --> $DIR/try-block-bad-lifetime.rs:41:26
    |
 LL |             Err(k) ?;
    |                 - value moved here
@@ -22,7 +33,7 @@ LL |         ::std::mem::drop(k); //~ ERROR use of moved value: `k`
    = note: move occurs because `k` has type `&mut i32`, which does not implement the `Copy` trait
 
 error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-bad-lifetime.rs:36:9
+  --> $DIR/try-block-bad-lifetime.rs:42:9
    |
 LL |         let k = &mut i;
    |                 ------ borrow of `i` occurs here
@@ -33,7 +44,7 @@ LL |
 LL |         let i_ptr = if let Err(i_ptr) = j { i_ptr } else { panic ! ("") };
    |                                         - borrow later used here
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
-Some errors occurred: E0382, E0506.
+Some errors occurred: E0382, E0506, E0597.
 For more information about an error, try `rustc --explain E0382`.

src/test/ui/try-block/try-block-bad-type.rs

@@ -8,21 +8,23 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 pub fn main() {
-    let res: Result<u32, i32> = do catch {
+    let res: Result<u32, i32> = try {
         Err("")?; //~ ERROR the trait bound `i32: std::convert::From<&str>` is not satisfied
         5
     };
 
-    let res: Result<i32, i32> = do catch {
+    let res: Result<i32, i32> = try {
         "" //~ ERROR type mismatch
     };
 
-    let res: Result<i32, i32> = do catch { }; //~ ERROR type mismatch
+    let res: Result<i32, i32> = try { }; //~ ERROR type mismatch
 
-    let res: () = do catch { }; //~ the trait bound `(): std::ops::Try` is not satisfied
+    let res: () = try { }; //~ the trait bound `(): std::ops::Try` is not satisfied
 
-    let res: i32 = do catch { 5 }; //~ ERROR the trait bound `i32: std::ops::Try` is not satisfied
+    let res: i32 = try { 5 }; //~ ERROR the trait bound `i32: std::ops::Try` is not satisfied
 }

src/test/ui/try-block/try-block-bad-type.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `i32: std::convert::From<&str>` is not satisfied
-  --> $DIR/catch-bad-type.rs:15:9
+  --> $DIR/try-block-bad-type.rs:17:9
    |
 LL |         Err("")?; //~ ERROR the trait bound `i32: std::convert::From<&str>` is not satisfied
    |         ^^^^^^^^ the trait `std::convert::From<&str>` is not implemented for `i32`
@@ -13,7 +13,7 @@ LL |         Err("")?; //~ ERROR the trait bound `i32: std::convert::From<&str>`
    = note: required by `std::convert::From::from`
 
 error[E0271]: type mismatch resolving `<std::result::Result<i32, i32> as std::ops::Try>::Ok == &str`
-  --> $DIR/catch-bad-type.rs:20:9
+  --> $DIR/try-block-bad-type.rs:22:9
    |
 LL |         "" //~ ERROR type mismatch
    |         ^^ expected i32, found &str
@@ -22,27 +22,27 @@ LL |         "" //~ ERROR type mismatch
               found type `&str`
 
 error[E0271]: type mismatch resolving `<std::result::Result<i32, i32> as std::ops::Try>::Ok == ()`
-  --> $DIR/catch-bad-type.rs:23:44
+  --> $DIR/try-block-bad-type.rs:25:39
    |
-LL |     let res: Result<i32, i32> = do catch { }; //~ ERROR type mismatch
-   |                                            ^ expected i32, found ()
+LL |     let res: Result<i32, i32> = try { }; //~ ERROR type mismatch
+   |                                       ^ expected i32, found ()
    |
    = note: expected type `i32`
               found type `()`
 
 error[E0277]: the trait bound `(): std::ops::Try` is not satisfied
-  --> $DIR/catch-bad-type.rs:25:28
+  --> $DIR/try-block-bad-type.rs:27:23
    |
-LL |     let res: () = do catch { }; //~ the trait bound `(): std::ops::Try` is not satisfied
-   |                            ^^^ the trait `std::ops::Try` is not implemented for `()`
+LL |     let res: () = try { }; //~ the trait bound `(): std::ops::Try` is not satisfied
+   |                       ^^^ the trait `std::ops::Try` is not implemented for `()`
    |
    = note: required by `std::ops::Try::from_ok`
 
 error[E0277]: the trait bound `i32: std::ops::Try` is not satisfied
-  --> $DIR/catch-bad-type.rs:27:29
+  --> $DIR/try-block-bad-type.rs:29:24
    |
-LL |     let res: i32 = do catch { 5 }; //~ ERROR the trait bound `i32: std::ops::Try` is not satisfied
-   |                             ^^^^^ the trait `std::ops::Try` is not implemented for `i32`
+LL |     let res: i32 = try { 5 }; //~ ERROR the trait bound `i32: std::ops::Try` is not satisfied
+   |                        ^^^^^ the trait `std::ops::Try` is not implemented for `i32`
    |
    = note: required by `std::ops::Try::from_ok`
 

src/test/ui/try-block/try-block-in-edition2015.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+// compile-flags: --edition 2015
+
+pub fn main() {
+    let try_result: Option<_> = try {
+    //~^ ERROR expected struct, variant or union type, found macro `try`
+        let x = 5; //~ ERROR expected identifier, found keyword
+        x
+    };
+    assert_eq!(try_result, Some(5));
+}

src/test/ui/try-block/try-block-in-edition2015.stderr

@@ -0,0 +1,18 @@
+error: expected identifier, found keyword `let`
+  --> $DIR/try-block-in-edition2015.rs:16:9
+   |
+LL |     let try_result: Option<_> = try {
+   |                                 --- while parsing this struct
+LL |     //~^ ERROR expected struct, variant or union type, found macro `try`
+LL |         let x = 5; //~ ERROR expected identifier, found keyword
+   |         ^^^ expected identifier, found keyword
+
+error[E0574]: expected struct, variant or union type, found macro `try`
+  --> $DIR/try-block-in-edition2015.rs:14:33
+   |
+LL |     let try_result: Option<_> = try {
+   |                                 ^^^ did you mean `try!(...)`?
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0574`.

src/test/ui/try-block/try-block-in-match.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 fn main() {
-    match do catch { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `do`
+    match try { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `try`
 }

src/test/ui/try-block/try-block-in-match.stderr

@@ -0,0 +1,8 @@
+error: expected expression, found reserved keyword `try`
+  --> $DIR/try-block-in-match.rs:16:11
+   |
+LL |     match try { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `try`
+   |           ^^^ expected expression
+
+error: aborting due to previous error
+

src/test/ui/try-block/try-block-in-while.rs

@@ -8,8 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 fn main() {
-    while do catch { false } {} //~ ERROR expected expression, found reserved keyword `do`
+    while try { false } {} //~ ERROR expected expression, found reserved keyword `try`
 }

src/test/ui/try-block/try-block-in-while.stderr

@@ -0,0 +1,8 @@
+error: expected expression, found reserved keyword `try`
+  --> $DIR/try-block-in-while.rs:16:11
+   |
+LL |     while try { false } {} //~ ERROR expected expression, found reserved keyword `try`
+   |           ^^^ expected expression
+
+error: aborting due to previous error
+

src/test/ui/try-block/try-block-maybe-bad-lifetime.rs

@@ -8,42 +8,48 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
 
-// This test checks that borrows made and returned inside catch blocks are properly constrained
+#![feature(try_blocks)]
+
+#![inline(never)]
+fn do_something_with<T>(_x: T) {}
+
+// This test checks that borrows made and returned inside try blocks are properly constrained
 pub fn main() {
     {
         // Test that a borrow which *might* be returned still freezes its referent
         let mut i = 222;
-        let x: Result<&i32, ()> = do catch {
+        let x: Result<&i32, ()> = try {
             Err(())?;
             &i
         };
-        x.ok().cloned();
         i = 0; //~ ERROR cannot assign to `i` because it is borrowed
         let _ = i;
+        do_something_with(x);
     }
 
     {
         let x = String::new();
-        let _y: Result<(), ()> = do catch {
+        let _y: Result<(), ()> = try {
             Err(())?;
             ::std::mem::drop(x);
         };
-        println!("{}", x); //~ ERROR use of moved value: `x`
+        println!("{}", x); //~ ERROR borrow of moved value: `x`
     }
 
     {
         // Test that a borrow which *might* be assigned to an outer variable still freezes
         // its referent
         let mut i = 222;
-        let j;
-        let x: Result<(), ()> = do catch {
+        let mut j = &-1;
+        let _x: Result<(), ()> = try {
             Err(())?;
             j = &i;
         };
         i = 0; //~ ERROR cannot assign to `i` because it is borrowed
         let _ = i;
+        do_something_with(j);
     }
 }
 

src/test/ui/try-block/try-block-maybe-bad-lifetime.stderr

@@ -1,31 +1,37 @@
 error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-maybe-bad-lifetime.rs:23:9
+  --> $DIR/try-block-maybe-bad-lifetime.rs:27:9
    |
 LL |             &i
-   |              - borrow of `i` occurs here
-...
+   |             -- borrow of `i` occurs here
+LL |         };
 LL |         i = 0; //~ ERROR cannot assign to `i` because it is borrowed
    |         ^^^^^ assignment to borrowed `i` occurs here
+LL |         let _ = i;
+LL |         do_something_with(x);
+   |                           - borrow later used here
 
-error[E0382]: use of moved value: `x`
-  --> $DIR/catch-maybe-bad-lifetime.rs:33:24
+error[E0382]: borrow of moved value: `x`
+  --> $DIR/try-block-maybe-bad-lifetime.rs:38:24
    |
 LL |             ::std::mem::drop(x);
    |                              - value moved here
 LL |         };
-LL |         println!("{}", x); //~ ERROR use of moved value: `x`
-   |                        ^ value used here after move
+LL |         println!("{}", x); //~ ERROR borrow of moved value: `x`
+   |                        ^ value borrowed here after move
    |
    = note: move occurs because `x` has type `std::string::String`, which does not implement the `Copy` trait
 
 error[E0506]: cannot assign to `i` because it is borrowed
-  --> $DIR/catch-maybe-bad-lifetime.rs:45:9
+  --> $DIR/try-block-maybe-bad-lifetime.rs:50:9
    |
 LL |             j = &i;
-   |                  - borrow of `i` occurs here
+   |                 -- borrow of `i` occurs here
 LL |         };
 LL |         i = 0; //~ ERROR cannot assign to `i` because it is borrowed
    |         ^^^^^ assignment to borrowed `i` occurs here
+LL |         let _ = i;
+LL |         do_something_with(j);
+   |                           - borrow later used here
 
 error: aborting due to 3 previous errors
 

src/test/ui/try-block/try-block-opt-init.rs

@@ -8,18 +8,20 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 fn use_val<T: Sized>(_x: T) {}
 
 pub fn main() {
     let cfg_res;
-    let _: Result<(), ()> = do catch {
+    let _: Result<(), ()> = try {
         Err(())?;
         cfg_res = 5;
         Ok::<(), ()>(())?;
         use_val(cfg_res);
     };
-    assert_eq!(cfg_res, 5); //~ ERROR use of possibly uninitialized variable
+    assert_eq!(cfg_res, 5); //~ ERROR borrow of possibly uninitialized variable: `cfg_res`
 }
 

src/test/ui/try-block/try-block-opt-init.stderr

@@ -1,7 +1,7 @@
 error[E0381]: borrow of possibly uninitialized variable: `cfg_res`
-  --> $DIR/catch-opt-init.rs:23:5
+  --> $DIR/try-block-opt-init.rs:25:5
    |
-LL |     assert_eq!(cfg_res, 5); //~ ERROR use of possibly uninitialized variable
+LL |     assert_eq!(cfg_res, 5); //~ ERROR borrow of possibly uninitialized variable: `cfg_res`
    |     ^^^^^^^^^^^^^^^^^^^^^^^ use of possibly uninitialized `cfg_res`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

src/test/ui/try-block/try-block-type-error.rs

@@ -8,18 +8,20 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(catch_expr)]
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
 
 fn foo() -> Option<()> { Some(()) }
 
 fn main() {
-    let _: Option<f32> = do catch {
+    let _: Option<f32> = try {
         foo()?;
         42
         //~^ ERROR type mismatch
     };
 
-    let _: Option<i32> = do catch {
+    let _: Option<i32> = try {
         foo()?;
     };
     //~^ ERROR type mismatch

src/test/ui/try-block/try-block-type-error.stderr

@@ -1,5 +1,5 @@
 error[E0271]: type mismatch resolving `<std::option::Option<f32> as std::ops::Try>::Ok == {integer}`
-  --> $DIR/catch-block-type-error.rs:18:9
+  --> $DIR/try-block-type-error.rs:20:9
    |
 LL |         42
    |         ^^
@@ -11,7 +11,7 @@ LL |         42
               found type `{integer}`
 
 error[E0271]: type mismatch resolving `<std::option::Option<i32> as std::ops::Try>::Ok == ()`
-  --> $DIR/catch-block-type-error.rs:24:5
+  --> $DIR/try-block-type-error.rs:26:5
    |
 LL |     };
    |     ^ expected i32, found ()