Rollup merge of rust-lang#70657 - lcnr:unused_delims_try, r=Centril

Allow `try`-blocks in places where an open delim is expected

Closes rust-lang#70490
Closes rust-lang#56828

r? @Centril

src/librustc_lint/unused.rs

@@ -384,7 +384,7 @@ trait UnusedDelimLint {
  fn is_expr_delims_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool {
  followed_by_block
  && match inner.kind {
- ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
+ ExprKind::Ret(_) | ExprKind::Break(..) => true,
  _ => parser::contains_exterior_struct_lit(&inner),
  }
  }

src/librustc_parse/parser/expr.rs

@@ -1846,11 +1846,9 @@ impl<'a> Parser<'a> {
  }
 
  fn is_try_block(&self) -> bool {
- self.token.is_keyword(kw::Try) &&
- self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
- self.token.uninterpolated_span().rust_2018() &&
- // Prevent `while try {} {}`, `if try {} {} else {}`, etc.
- !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+ self.token.is_keyword(kw::Try)
+ && self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
+ && self.token.uninterpolated_span().rust_2018()
  }
 
  /// Parses an `async move? {...}` expression.

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

@@ -1,7 +1,11 @@
+// run-pass
 // compile-flags: --edition 2018
 
 #![feature(try_blocks)]
 
 fn main() {
- match try { false } { _ => {} } //~ ERROR expected expression, found reserved keyword `try`
+ match try { } {
+ Err(()) => (),
+ Ok(()) => (),
+ }
 }

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

@@ -3,5 +3,6 @@
 #![feature(try_blocks)]
 
 fn main() {
- while try { false } {} //~ ERROR expected expression, found reserved keyword `try`
+ while try { false } {}
+ //~^ ERROR the trait bound `bool: std::ops::Try` is not satisfied
 }

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

@@ -1,8 +1,11 @@
-error: expected expression, found reserved keyword `try`
- --> $DIR/try-block-in-while.rs:6:11
+error[E0277]: the trait bound `bool: std::ops::Try` is not satisfied
+ --> $DIR/try-block-in-while.rs:6:15
  |
 LL | while try { false } {}
- | ^^^ expected expression
+ | ^^^^^^^^^ the trait `std::ops::Try` is not implemented for `bool`
+ |
+ = note: required by `std::ops::Try::from_ok`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/try-block/try-block-unused-delims.rs

@@ -0,0 +1,28 @@
+// check-pass
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
+#![warn(unused_parens, unused_braces)]
+
+fn consume<T>(_: Result<T, T>) -> T { todo!() }
+
+fn main() {
+ consume((try {}));
+ //~^ WARN unnecessary parentheses
+
+ consume({ try {} });
+ //~^ WARN unnecessary braces
+
+ match (try {}) {
+ //~^ WARN unnecessary parentheses
+ Ok(()) | Err(()) => (),
+ }
+
+ if let Err(()) = (try {}) {}
+ //~^ WARN unnecessary parentheses
+
+ match (try {}) {
+ //~^ WARN unnecessary parentheses
+ Ok(()) | Err(()) => (),
+ }
+}

src/test/ui/try-block/try-block-unused-delims.stderr

@@ -0,0 +1,44 @@
+warning: unnecessary parentheses around function argument
+ --> $DIR/try-block-unused-delims.rs:10:13
+ |
+LL | consume((try {}));
+ | ^^^^^^^^ help: remove these parentheses
+ |
+note: the lint level is defined here
+ --> $DIR/try-block-unused-delims.rs:5:9
+ |
+LL | #![warn(unused_parens, unused_braces)]
+ | ^^^^^^^^^^^^^
+
+warning: unnecessary braces around function argument
+ --> $DIR/try-block-unused-delims.rs:13:13
+ |
+LL | consume({ try {} });
+ | ^^^^^^^^^^ help: remove these braces
+ |
+note: the lint level is defined here
+ --> $DIR/try-block-unused-delims.rs:5:24
+ |
+LL | #![warn(unused_parens, unused_braces)]
+ | ^^^^^^^^^^^^^
+
+warning: unnecessary parentheses around `match` scrutinee expression
+ --> $DIR/try-block-unused-delims.rs:16:11
+ |
+LL | match (try {}) {
+ | ^^^^^^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around `let` scrutinee expression
+ --> $DIR/try-block-unused-delims.rs:21:22
+ |
+LL | if let Err(()) = (try {}) {}
+ | ^^^^^^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around `match` scrutinee expression
+ --> $DIR/try-block-unused-delims.rs:24:11
+ |
+LL | match (try {}) {
+ | ^^^^^^^^ help: remove these parentheses
+
+warning: 5 warnings emitted
+