Special error when using catch after try

Author: Kampfkarren

src/libsyntax/parse/parser.rs

@@ -3618,7 +3618,13 @@ impl<'a> Parser<'a> {
     {
         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
         attrs.extend(iattrs);
-        Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
+        if self.eat_keyword(keywords::Catch) {
+            let mut error = self.struct_span_err(self.prev_span, "`try {} catch` is not a valid syntax");
+            error.help("try using `match` on the result of the `try` block instead");
+            Err(error)
+        } else {
+            Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
+        }
     }
 
     // `match` token already eaten

src/test/ui/try-block/try-block-catch.rs

@@ -0,0 +1,9 @@
+// compile-flags: --edition 2018
+
+#![feature(try_blocks)]
+
+fn main() {
+	let res: Option<bool> = try {
+		true
+	} catch { }; //~ ERROR `try {} catch` is not a valid syntax
+}

src/test/ui/try-block/try-block-catch.stderr

@@ -0,0 +1,10 @@
+error: `try {} catch` is not a valid syntax
+  --> $DIR/try-block-catch.rs:8:4
+   |
+LL |     } catch { }; //~ ERROR `try {} catch` is not a valid syntax
+   |       ^^^^^
+   |
+   = help: try using `match` on the result of the `try` block instead
+
+error: aborting due to previous error
+