fix: quote ambiguous numeric strings starting with . or + (fixes #249)

packages/toon/src/shared/validation.ts

@@ -1,7 +1,7 @@
 import { DEFAULT_DELIMITER, LIST_ITEM_MARKER } from '../constants'
 import { isBooleanOrNullLiteral } from './literal-utils'
 
-const NUMERIC_LIKE_PATTERN = /^-?\d+(?:\.\d+)?(?:e[+-]?\d+)?$/i
+const NUMERIC_LIKE_PATTERN = /^[+-]?(\d+(?:\.\d*)?|\.\d+)(?:e[+-]?\d+)?$/i
 const LEADING_ZERO_PATTERN = /^0\d+$/
 
 /**

packages/toon/test/issue-249.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, it } from 'vitest'
+import { decode, encode } from '../src/index'
+
+describe('Issue 249', () => {
+  it('should preserve strings starting with dot or plus followed by numbers', () => {
+    const indent: number = 1;
+
+    function encodeToon(data: any): string {
+      return encode(data, { indent });
+    }
+
+    function decodeToon<T>(toon: string): T {
+      return decode(toon, { indent }) as any;
+    }
+
+    const data = [
+      '.6226633103089010',
+      '+8613334445577',
+    ]
+
+    // Expecting that it properly encodes these strings so that they decode back to strings
+    // If it encodes them as raw numbers in TOON format without quotes, they might be read back as numbers.
+    const encoded = encodeToon(data);
+    console.log('Encoded:', encoded);
+
+    // Encoded values MUST be quoted to avoid ambiguity with numbers
+    // This assertion will fail initially
+    expect(encoded).toContain('".6226633103089010"');
+    expect(encoded).toContain('"+8613334445577"');
+
+    const decoded = decodeToon(encoded);
+
+    expect(decoded).toEqual(data);
+  })
+})