fix: use Int32Array for signed VLQ delta decoding in readMappings

lib/helpers/readMappings.js

@@ -35,8 +35,8 @@
  * @returns {void}
  */
 const readMappings = (mappings, onMapping) => {
-	// generatedColumn, [sourceIndex, originalLine, orignalColumn, [nameIndex]]
-	const currentData = new Uint32Array([0, 0, 1, 0, 0]);
+	// generatedColumn, [sourceIndex, originalLine, originalColumn, [nameIndex]]
+	const currentData = new Int32Array([0, 0, 1, 0, 0]);
 	let currentDataPos = 0;
 	// currentValue will include a sign bit at bit 0
 	let currentValue = 0;
@@ -116,5 +116,4 @@
 		);
 	}
 };
-
 module.exports = readMappings;

test/readMapping.js

@@ -0,0 +1,76 @@
+"use strict";
+
+const readMappings = require("../lib/helpers/readMappings");
+
+describe("readMappings", () => {
+	it("should correctly decode negative VLQ deltas (backwards column references)", () => {
+		const mappings = [];
+
+		// Mapping with a negative column delta (backwards reference)
+		readMappings(
+			"AAKA;CAAC",
+			(
+				generatedLine,
+				generatedColumn,
+				sourceIndex,
+				originalLine,
+				originalColumn,
+				nameIndex,
+			) => {
+				mappings.push({
+					generatedLine,
+					generatedColumn,
+					sourceIndex,
+					originalLine,
+					originalColumn,
+					nameIndex,
+				});
+			},
+		);
+
+		expect(mappings).toHaveLength(2);
+
+		// First mapping: line 1, col 0, source 0, orig line 5, orig col 0
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[0].generatedColumn).toBe(0);
+		expect(mappings[0].sourceIndex).toBe(0);
+		expect(mappings[0].originalLine).toBe(5);
+		expect(mappings[0].originalColumn).toBe(0);
+
+		// Second mapping: line 2 — negative delta on originalColumn (col goes backwards)
+		expect(mappings[1].generatedLine).toBe(2);
+		expect(mappings[1].generatedColumn).toBe(1);
+		expect(mappings[1].sourceIndex).toBe(1);
+		expect(mappings[1].originalLine).toBe(5);
+		expect(mappings[1].originalColumn).toBe(-1);
+	});
+
+	it("should handle mappings without source info", () => {
+		const mappings = [];
+
+		readMappings("A", (generatedLine, generatedColumn, sourceIndex) => {
+			mappings.push({ generatedLine, generatedColumn, sourceIndex });
+		});
+
+		expect(mappings).toHaveLength(1);
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[0].generatedColumn).toBe(0);
+		expect(mappings[0].sourceIndex).toBe(-1);
+	});
+
+	it("should handle multiple lines", () => {
+		const mappings = [];
+
+		readMappings(
+			"AAAA;AACA;AACA",
+			(generatedLine, generatedColumn, sourceIndex, originalLine) => {
+				mappings.push({ generatedLine, generatedColumn, originalLine });
+			},
+		);
+
+		expect(mappings).toHaveLength(3);
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[1].generatedLine).toBe(2);
+		expect(mappings[2].generatedLine).toBe(3);
+	});
+});