Preserve ZERO WIDTH JOINER in legacy joining defaults

ArabicShaping files before Unicode 3.1.1 omit joining controls. The fallback excluded ZWJ from Transparent but placed it in Non_Joining, despite its join-causing semantics. Seed Join_Causing with U+200D and allow explicit shaping records to override the defaults.

Cover both joining controls and neighboring joining types across historical and derived-data releases. Only U+200D changes in the eight releases from Unicode 2.0.14 through 3.1.0.

Assisted-By: GPT-6
Issue: #110

Author: JLHwung

scripts/parse-joining-type.mjs

@@ -56,7 +56,13 @@ const parseArabicShaping = (source, categories) => {
 		.remove(0x200d);
 	const map = {
 		Transparent: transparent,
-		Non_Joining: regenerate().addRange(0, 0x10ffff).remove(transparent),
+		// Before Unicode 3.1.1, ArabicShaping omits the joining controls.
+		// ZWJ still causes cursive joining; ZWNJ remains Non_Joining.
+		Join_Causing: regenerate(0x200d),
+		Non_Joining: regenerate()
+			.addRange(0, 0x10ffff)
+			.remove(transparent)
+			.remove(0x200d),
 	};
 	const lines = source.split('\n');
 	for (const line of lines) {
@@ -71,6 +77,7 @@ const parseArabicShaping = (source, categories) => {
 		const codePoint = parseInt(data[0].trim(), 16);
 		const joiningType = findCanonicalName(data[2].trim());
 		map.Transparent.remove(codePoint);
+		map.Join_Causing.remove(codePoint);
 		map.Non_Joining.remove(codePoint);
 		map[joiningType] ??= regenerate();
 		map[joiningType].add(codePoint);

tests/legacy-joining.mjs

@@ -0,0 +1,34 @@
+import { test } from 'node:test';
+import parseJoiningType from '../scripts/parse-joining-type.mjs';
+
+test('Legacy joining data preserves both joining controls', async (t) => {
+	for (const version of [
+		'2.0.14',
+		'2.1.2',
+		'2.1.5',
+		'2.1.8',
+		'2.1.9',
+		'3.0.0',
+		'3.0.1',
+		'3.1.0',
+		'3.1.1',
+		'3.2.0',
+		'4.0.1',
+	]) {
+		const map = await parseJoiningType(version);
+		for (const [cp, expected] of [
+			[0x200c, 'Non_Joining'],
+			[0x200d, 'Join_Causing'],
+			[0x300, 'Transparent'],
+			[0x640, 'Join_Causing'],
+		]) {
+			t.assert.deepEqual(
+				Object.entries(map)
+					.filter(([, set]) => set.contains(cp))
+					.map(([value]) => value),
+				[expected],
+				`${version}: U+${cp.toString(16).toUpperCase()}`,
+			);
+		}
+	}
+});

tests/tests.mjs

@@ -4,6 +4,7 @@ import { fileURLToPath } from 'node:url';
 import { suite, test } from 'node:test';
 import './parsers.mjs';
 import './legacy-names.mjs';
+import './legacy-joining.mjs';
 import './line-endings.mjs';
 import resources from '../data/resources.mjs';