Add regression test for rust-lang#81827

Author: JohnTitor

src/test/ui/parser/issue-81827.rs

@@ -0,0 +1,11 @@
+// error-pattern: this file contains an unclosed delimiter
+// error-pattern: mismatched closing delimiter: `]`
+// error-pattern: expected one of `)` or `,`, found `{`
+
+#![crate_name="0"]
+
+
+
+fn main() {}
+
+fn r()->i{0|{#[cfg(r(0{]0

src/test/ui/parser/issue-81827.stderr

@@ -0,0 +1,35 @@
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-81827.rs:11:27
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |          -  -             ^
+   |          |  |
+   |          |  unclosed delimiter
+   |          unclosed delimiter
+
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-81827.rs:11:27
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |          -  -             ^
+   |          |  |
+   |          |  unclosed delimiter
+   |          unclosed delimiter
+
+error: mismatched closing delimiter: `]`
+  --> $DIR/issue-81827.rs:11:23
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |               -       ^^ mismatched closing delimiter
+   |               |       |
+   |               |       unclosed delimiter
+   |               closing delimiter possibly meant for this
+
+error: expected one of `)` or `,`, found `{`
+  --> $DIR/issue-81827.rs:11:23
+   |
+LL | fn r()->i{0|{#[cfg(r(0{]0
+   |                       ^ expected one of `)` or `,`
+
+error: aborting due to 4 previous errors
+