Let the narrower block entry win in legacy block data

The Unicode 2.0 blocks file lists FE70..FEFF as Arabic Presentation
Forms-B and FEFF..FEFF as Specials, so U+FEFF belonged to both blocks in
Unicode 2.0.14 through 2.1.8. Apply narrower ranges last so the more
specific Specials entry wins, matching the corrected Unicode 2.1.9 file.

Assisted-By: Claude Opus 5.5

Author: JLHwung

scripts/parse-blocks-scripts-properties.mjs

@@ -306,6 +306,7 @@ const parseBlocks = async (version) => {
 			return;
 		}
 		map = {};
+		const records = [];
 		for (const line of source.trimEnd().split('\n')) {
 			const record = line.split('#')[0].trim();
 			if (!record) {
@@ -316,7 +317,21 @@ const parseBlocks = async (version) => {
 				.map((field) => field.trim());
 			const canonicalBlockName = looseMatch('Block', blockName).value;
 			map[canonicalBlockName] ??= regenerate();
-			map[canonicalBlockName].addRange(parseInt(start, 16), parseInt(end, 16));
+			records.push({
+				block: canonicalBlockName,
+				start: parseInt(start, 16),
+				end: parseInt(end, 16),
+			});
+		}
+		// The Unicode 2.0 blocks file lists FE70..FEFF as Arabic Presentation
+		// Forms-B and FEFF..FEFF as Specials. Apply narrower ranges last so the
+		// more specific entry wins, as the corrected Unicode 2.1.9 file does.
+		records.sort((a, b) => b.end - b.start - (a.end - a.start));
+		for (const { block, start, end } of records) {
+			for (const codePoints of Object.values(map)) {
+				codePoints.removeRange(start, end);
+			}
+			map[block].addRange(start, end);
 		}
 	} else {
 		map = await parseBlocksScriptsProperties('blocks', version);

tests/parsers.mjs

@@ -59,8 +59,7 @@ test('Historical titlecase digraphs retain their identity mapping', async (t) =>
 });
 
 test('Block values cover Unicode, including No_Block gaps', async (t) => {
-	// Earlier files overlap Arabic Presentation Forms-B and Specials at U+FEFF.
-	for (const version of ['2.1.9', '3.1.0', '18.0.0']) {
+	for (const version of ['2.0.14', '2.1.8', '2.1.9', '3.1.0', '18.0.0']) {
 		const blocks = await parseBlocks(version);
 		t.assert.ok(blocks.No_Block.contains(0x40000), version);
 		t.assert.ok(!blocks.No_Block.contains(0x41), version);
@@ -99,12 +98,10 @@ test('Legacy blocks retain every discontiguous Specials range', async (t) => {
 		t.assert.ok(blocks.Specials.contains(0xfffd), version);
 		t.assert.ok(!blocks.Specials.contains(0xff00), version);
 		t.assert.ok(!blocks.No_Block.contains(0xfeff), version);
-		// Preserve the overlap explicitly recorded by the earliest source files.
-		t.assert.equal(
-			blocks.Arabic_Presentation_Forms_B.contains(0xfeff),
-			['2.0.14', '2.1.2', '2.1.5', '2.1.8'].includes(version),
-			version,
-		);
+		// The earliest source files also list U+FEFF in Arabic Presentation
+		// Forms-B. The more specific Specials entry wins.
+		t.assert.ok(!blocks.Arabic_Presentation_Forms_B.contains(0xfeff), version);
+		t.assert.ok(blocks.Arabic_Presentation_Forms_B.contains(0xfefe), version);
 	}
 });