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 #52604 That was fixed by PR #53135
cc #31436 #50412

Author: bors

src/doc/unstable-book/src/language-features/catch-expr.md renamed to src/doc/unstable-book/src/language-features/try-blocks.md

@@ -1,27 +1,29 @@
-# `catch_expr`
+# `try_blocks`
 
 The tracking issue for this feature is: [#31436]
 
 [#31436]: https://github.com/rust-lang/rust/issues/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 {