fix: Prevent infinite loop on empty input

Author: matz3

src/MagicString.js

@@ -660,12 +660,18 @@ export default class MagicString {
 		if (DEBUG) this.stats.time('_split');
 
 		let chunk = this.lastSearchedChunk;
+		let previousChunk = chunk;
 		const searchForward = index > chunk.end;
 
 		while (chunk) {
 			if (chunk.contains(index)) return this._splitChunk(chunk, index);
 
 			chunk = searchForward ? this.byStart[chunk.end] : this.byEnd[chunk.start];
+			
+			// Prevent infinite loop (e.g. via empty chunks, where start === end)
+			if (chunk === previousChunk) return;
+
+			previousChunk = chunk;
 		}
 	}
 

test/MagicString.test.js

@@ -98,6 +98,26 @@ describe('MagicString', () => {
 
 			assert.equal(s.toString(), 'x4213');
 		});
+
+		it('should append/prepend at end of string when index is out of upper bound', () => {
+			const s = new MagicString('x');
+			s.prependLeft(6, 'A');
+			s.appendLeft(6, 'B');
+			s.prependRight(6, 'C');
+			s.appendRight(6, 'D');
+
+			assert.equal(s.toString(), 'ABxCD');
+		});
+
+		it('should append/prepend on empty string when index is out of upper bound', () => {
+			const s = new MagicString('');
+			s.prependLeft(6, 'A');
+			s.appendLeft(6, 'B');
+			s.prependRight(6, 'C');
+			s.appendRight(6, 'D');
+
+			assert.equal(s.toString(), 'ABCD');
+		});
 	});
 
 	describe('appendLeft', () => {