Test/lexer unicode pattern white space

tests/ui/lexer/unicode-pattern-white-space.rs

@@ -0,0 +1,12 @@
+//@ run-pass
+// Test that the Rust lexer accepts vertical tab (\x0B) as valid whitespace
+// between tokens. Vertical tab is part of Unicode Pattern_White_Space, which
+// the Rust language specification uses to define whitespace tokens.
+// See: https://unicode.org/reports/tr31/#Pattern_White_Space
+//
+// The space between "let" and "_" below is a vertical tab character (\x0B),
+// not a regular space.
+
+fn main() {
+    let_ = 1;
+}