Add test to check unicode identifier version

Author: ehuss

Diff for: compiler/rustc_lexer/src/lib.rs

@@ -33,6 +33,7 @@ pub mod unescape;
 mod tests;
 
 use unicode_properties::UnicodeEmoji;
+pub use unicode_xid::UNICODE_VERSION as UNICODE_XID_VERSION;
 
 use self::LiteralKind::*;
 use self::TokenKind::*;

Diff for: compiler/rustc_parse/src/lib.rs

@@ -24,6 +24,7 @@ use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Diag, FatalError, PResult};
 use rustc_session::parse::ParseSess;
 use rustc_span::{FileName, SourceFile, Span};
+pub use unicode_normalization::UNICODE_VERSION as UNICODE_NORMALIZATION_VERSION;
 
 pub const MACRO_ARGUMENTS: Option<&str> = Some("macro arguments");
 

Diff for: tests/ui-fulldeps/lexer/unicode-version.rs

@@ -0,0 +1,27 @@
+// This test is used to validate which version of Unicode is used for parsing
+// identifiers. If the Unicode version changes, it should also be updated in
+// the reference at
+// https://github.com/rust-lang/reference/blob/HEAD/src/identifiers.md.
+
+//@ run-pass
+//@ check-run-results
+//@ ignore-cross-compile
+//@ reference: ident.unicode
+//@ reference: ident.normalization
+
+#![feature(rustc_private)]
+
+extern crate rustc_driver;
+extern crate rustc_lexer;
+extern crate rustc_parse;
+
+fn main() {
+    println!("Checking if Unicode version changed.");
+    println!(
+        "If the Unicode version changes are intentional, \
+         it should also be updated in the reference at \
+         https://github.com/rust-lang/reference/blob/HEAD/src/identifiers.md."
+    );
+    println!("Unicode XID version is: {:?}", rustc_lexer::UNICODE_XID_VERSION);
+    println!("Unicode normalization version is: {:?}", rustc_parse::UNICODE_NORMALIZATION_VERSION);
+}

Diff for: tests/ui-fulldeps/lexer/unicode-version.run.stdout

@@ -0,0 +1,4 @@
+Checking if Unicode version changed.
+If the Unicode version changes are intentional, it should also be updated in the reference at https://github.com/rust-lang/reference/blob/HEAD/src/identifiers.md.
+Unicode XID version is: (16, 0, 0)
+Unicode normalization version is: (16, 0, 0)

Diff for: triagebot.toml

@@ -991,6 +991,13 @@ cc = ["@Zalathar"]
 [mentions."src/tools/opt-dist"]
 cc = ["@kobzol"]
 
+[mentions."tests/ui-fulldeps/lexer/unicode-version.run.stdout"]
+message = """If the Unicode version changes are intentional,
+it should also be updated in the reference at
+https://github.com/rust-lang/reference/blob/HEAD/src/identifiers.md.
+"""
+cc = ["@ehuss"]
+
 [assign]
 warn_non_default_branch = true
 contributing_url = "https://rustc-dev-guide.rust-lang.org/getting-started.html"