Fix pluralization issues in translations

build/intl-linter/rules/pluralPound.ts

@@ -0,0 +1,37 @@
+// Copyright 2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { PluralElement } from '@formatjs/icu-messageformat-parser';
+import { rule } from '../utils/rule';
+
+export default rule('pluralPound', context => {
+  const stack: Array<PluralElement> = [];
+  return {
+    enterPlural(element) {
+      stack.push(element);
+    },
+    exitPlural() {
+      stack.pop();
+    },
+    enterLiteral(element, parent) {
+      // Note: Without the stack this could be turned into a rule to check for
+      // explicit numbers anywhere in the message.
+      if (parent == null) {
+        return;
+      }
+      if (parent !== stack.at(-1)) {
+        return;
+      }
+      // Adapted from https://github.com/TalhaAwan/get-numbers
+      // Checks for explicit whitespace before and after the number.
+      const index = element.value.search(/(^| )(-\d+|\d+)(,\d+)*(\.\d+)*($| )/);
+      if (index > -1) {
+        context.report(
+          'Use # instead of an explicit number',
+          element.location,
+          index
+        );
+      }
+    },
+  };
+});