add testcase for 127868

Author: chenyukang

Diff for: tests/ui/parser/mismatched-delimiter-corner-case-issue-127868.rs

@@ -0,0 +1,7 @@
+// ignore-tidy-trailing-newlines
+// issue: rust-lang/rust#127868
+
+fn main() {
+    let a = [[[[[[[[[[[[[[[[[[[[1, {, (, [,;
+} //~ ERROR mismatched closing delimiter: `}`
+//~ ERROR this file contains an unclosed delimiter

Diff for: tests/ui/parser/mismatched-delimiter-corner-case-issue-127868.stderr

@@ -0,0 +1,45 @@
+error: mismatched closing delimiter: `}`
+  --> $DIR/mismatched-delimiter-corner-case-issue-127868.rs:5:42
+   |
+LL | fn main() {
+   |           - closing delimiter possibly meant for this
+LL |     let a = [[[[[[[[[[[[[[[[[[[[1, {, (, [,;
+   |                                          ^ unclosed delimiter
+LL | }
+   | ^ mismatched closing delimiter
+
+error: this file contains an unclosed delimiter
+  --> $DIR/mismatched-delimiter-corner-case-issue-127868.rs:7:51
+   |
+LL | fn main() {
+   |           - unclosed delimiter
+LL |     let a = [[[[[[[[[[[[[[[[[[[[1, {, (, [,;
+   |             --------------------   - this delimiter might not be properly closed...
+   |             ||||||||||||||||||||
+   |             |||||||||||||||||||unclosed delimiter
+   |             ||||||||||||||||||unclosed delimiter
+   |             |||||||||||||||||unclosed delimiter
+   |             ||||||||||||||||unclosed delimiter
+   |             |||||||||||||||unclosed delimiter
+   |             ||||||||||||||unclosed delimiter
+   |             |||||||||||||unclosed delimiter
+   |             ||||||||||||unclosed delimiter
+   |             |||||||||||unclosed delimiter
+   |             ||||||||||unclosed delimiter
+   |             |||||||||unclosed delimiter
+   |             ||||||||unclosed delimiter
+   |             |||||||unclosed delimiter
+   |             ||||||unclosed delimiter
+   |             |||||unclosed delimiter
+   |             ||||unclosed delimiter
+   |             |||unclosed delimiter
+   |             ||unclosed delimiter
+   |             |unclosed delimiter
+   |             unclosed delimiter
+LL | }
+   | - ...as it matches this but it has different indentation
+LL |
+   |                                                   ^
+
+error: aborting due to 2 previous errors
+