test(lexer): Ensure frontmatter can contain unicode whitespace

Author: epage

tests/ui/frontmatter/frontmatter-contains-whitespace.rs

@@ -0,0 +1,22 @@
+#!/usr/bin/env -S cargo -Zscript
+---cargo
+# Beware editing: it has numerous whitespace characters which are important.
+# It contains one ranges from the 'PATTERN_WHITE_SPACE' property outlined in
+# https://unicode.org/Public/UNIDATA/PropList.txt
+#
+# The characters in the first expression of the assertion can be generated
+# from: "4\u{0C}+\n\t\r7\t*\u{20}2\u{85}/\u{200E}3\u{200F}*\u{2028}2\u{2029}"
+package.description = """
+4+
+
+7   * 2…/‎3‏*
2
+"""
+---
+
+//@ check-pass
+
+// Ensure the frontmatter can contain any whitespace
+
+#![feature(frontmatter)]
+
+fn main() {}