Fix: Update parseSyntaxError to use lossless-json for accurate error locations

lib/__tests__/json-utils.test.ts

@@ -11,10 +11,68 @@ import {
   escapeForCode,
   parseJson5Compat,
   diffLines,
+  validate,
 } from "../json-utils";
 
 const BIG = '{"id":12345678901234567890,"pi":3.141592653589793238,"n":42}';
 
+describe("JSON Formatter Error Locations", () => {
+  it("extracts correct location for unquoted values", () => {
+    const result = validate('{"a": x}');
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(1);
+      expect(result.error.column).toBe(7);
+    }
+  });
+
+  it("extracts correct location for multi-line JSON", () => {
+    const input = '{"a": 1,\n"b": tru\n}';
+    const result = validate(input);
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(2);
+      expect(result.error.column).toBe(6);
+    }
+  });
+
+  it("keeps original location for duplicate keys with trailing comma", () => {
+    const result = validate('{"a":1,"a":2,}');
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(1);
+      expect(result.error.column).toBe(14);
+    }
+  });
+
+  it("extracts correct location for unexpected end of input", () => {
+    const result = validate('{"a": ');
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(1);
+      expect(result.error.column).toBe(7);
+    }
+  });
+
+  it("extracts correct location for undefined in array", () => {
+    const result = validate('[1, 2, undefined]');
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(1);
+      expect(result.error.column).toBe(8);
+    }
+  });
+
+  it("keeps existing correct locations intact", () => {
+    const result = validate('{"a":1,}');
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.line).toBe(1);
+      expect(result.error.column).toBe(8);
+    }
+  });
+});
+
 describe("lossless numbers", () => {
   it("preserves large integers and long decimals when formatting", () => {
     const r = format(BIG, 2);

lib/json-utils.ts

@@ -35,9 +35,11 @@ function parseSyntaxError(raw: string, err: unknown): JsonError {
   const msg = err instanceof Error ? err.message : String(err);
   const posMatch = msg.match(/position (\d+)/i);
   const lineMatch = msg.match(/line (\d+) column (\d+)/i);
+
   let line = 1;
   let column = 1;
   let position = 0;
+
   if (posMatch) {
     position = parseInt(posMatch[1], 10);
     const lc = computeLineCol(raw, position);
@@ -46,11 +48,26 @@ function parseSyntaxError(raw: string, err: unknown): JsonError {
   } else if (lineMatch) {
     line = parseInt(lineMatch[1], 10);
     column = parseInt(lineMatch[2], 10);
+  } else {
+    try {
+      llParse(raw);
+    } catch (llError) {
+      if (llError instanceof Error) {
+        const llPosMatch = llError.message.match(/position (\d+)/i);
+        if (llPosMatch) {
+          position = parseInt(llPosMatch[1], 10);
+          const lc = computeLineCol(raw, position);
+          line = lc.line;
+          column = lc.column;
+        }
+      }
+    }
   }
+
   const suggestion = suggestFix(raw);
   return { message: msg.replace(/in JSON.*$/, "").trim() || "Invalid JSON", line, column, position, suggestion };
 }
-
+ 
 export function validate(raw: string): Result<true> {
   if (!raw.trim()) {
     return {