1 files changed, 46 insertions, 0 deletions

diff --git a/subprojects/frontend/src/language/tokens.ts b/subprojects/frontend/src/language/tokens.ts
new file mode 100644
index 00000000..b5d022f1
--- /dev/null
+++ b/subprojects/frontend/src/language/tokens.ts
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2018-2024 by Marijn Haverbeke <marijnh@gmail.com> and others
+ * Copyright (C) 2024 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: MIT AND EPL-2.0
+ *
+ * Based on the CSS tokenizer at
+ * https://github.com/lezer-parser/css/blob/790568c968a660a94bf0fbd97a86c66da1c529e5/src/tokens.js
+ */
+
+import { ExternalTokenizer } from '@lezer/lr';
+
+/* eslint-disable-next-line import/no-unresolved --
+  Synthetic import from `@lezer/generator/rollup` cannot be found by ESLint.
+*/
+import { QualifiedNameSeparator } from './problem.grammar.terms';
+
+const colon = 58;
+const underscore = 95;
+
+function isAlpha(ch: number) {
+  return (ch >= 65 && ch <= 90) || (ch >= 97 && ch <= 122) || ch >= 161;
+}
+
+function isDigit(ch: number) {
+  return ch >= 48 && ch <= 57;
+}
+
+function isIdentifier(ch: number) {
+  return isAlpha(ch) || isDigit(ch) || ch === underscore;
+}
+
+/* eslint-disable-next-line import/prefer-default-export --
+  Lezer requires a named export.
+*/
+export const qualifiedNameSeparator = new ExternalTokenizer((input) => {
+  if (input.peek(0) === colon && input.peek(1) === colon) {
+    const previous = input.peek(-1);
+    if (isIdentifier(previous)) {
+      // Inject an extra 0-length token into the token stream to let Lezer
+      // consume the `::` on its own. Explicitly consuming 2 characters here
+      // leads to inconsistent highlighting of qualified names.
+      input.acceptToken(QualifiedNameSeparator);
+    }
+  }
+});