fix(decode): prevent false array header detection for unquoted keys c…

[rayriffy]

Linked Issue

Closes #

Description

This PR fixes a bug in the decoder where standard key-value pairs were mistakenly parsed as array headers.

Previously, if the parser encountered an unquoted key or value string containing both brackets and colons (e.g., display: "(Hello) [World] this (is:test)"), it would find the first [ and assume it was parsing an array header. When it subsequently found the : later in the string, it would throw a SyntaxError: Unexpected content ... between bracket segment and colon.

This fix updates parseArrayHeaderLine to check if a colon (:) appears before the first bracket ([). If it does, the parser correctly identifies it as a key-value separator and aborts the array header parsing.

To replicate:

import { encode, decode } from './src'

const jsonSource = {
  message: "Hello [world] this is a test:"
}

const payload = encode(jsonSource)
console.log("Encoded TOON payload:")
console.log(payload)

console.log("\nDecoded object:")
console.log(decode(payload))

returns following result

❯ bun ./repro.ts  
Encoded TOON payload:
message: "Hello [world] this is a test:"

Decoded object:
12 |   /** Raw source line (including indentation) where the error was detected, if known. */
13 |   readonly source?: string
14 | 
15 |   constructor(message: string, context?: { line?: number, source?: string, cause?: unknown }) {
16 |     const prefix = context?.line !== undefined ? `Line ${context.line}: ` : ''
17 |     super(prefix + message, context?.cause !== undefined ? { cause: context.cause } : undefined)
     ^
ToonDecodeError: Line 1: Unexpected content "this is a test" between bracket segment and colon
   line: 1,
 source: "message: \"Hello [world] this is a test:\"",

      at <parse> ()
      at new ToonDecodeError (/Users/rayriffy/Git/toon/packages/toon/src/decode/errors.ts:17:5)
      at withLine (/Users/rayriffy/Git/toon/packages/toon/src/decode/errors.ts:39:17)
      at decodeKeyValueSync (/Users/rayriffy/Git/toon/packages/toon/src/decode/decoders.ts:368:14)
      at decodeStreamSync (/Users/rayriffy/Git/toon/packages/toon/src/decode/decoders.ts:299:5)
      at buildValueFromEvents (/Users/rayriffy/Git/toon/packages/toon/src/decode/event-builder.ts:60:9)
      at decodeFromLines (/Users/rayriffy/Git/toon/packages/toon/src/index.ts:146:24)

79 |   const gapStart = Math.max(bracketEnd + 1, braceEnd)
80 |   const gapBeforeColon = content.slice(gapStart, colonIndex)
81 |   if (gapBeforeColon !== '') {
82 |     if (strict) {
83 |       const trimmedGap = gapBeforeColon.trim()
84 |       throw new SyntaxError(trimmedGap === ''
                     ^
SyntaxError: Unexpected content "this is a test" between bracket segment and colon
      at parseArrayHeaderLine (/Users/rayriffy/Git/toon/packages/toon/src/decode/parser.ts:84:17)
      at withLine (/Users/rayriffy/Git/toon/packages/toon/src/decode/errors.ts:33:12)
      at decodeKeyValueSync (/Users/rayriffy/Git/toon/packages/toon/src/decode/decoders.ts:217:23)
      at decodeStreamSync (/Users/rayriffy/Git/toon/packages/toon/src/decode/decoders.ts:179:10)
      at buildValueFromEvents (/Users/rayriffy/Git/toon/packages/toon/src/decode/event-builder.ts:22:14)
      at decodeFromLines (/Users/rayriffy/Git/toon/packages/toon/src/index.ts:146:24)
      at /Users/rayriffy/Git/toon/packages/toon/repro.ts:12:13

Bun v1.3.14 (macOS arm64)

following the fix

❯ bun ./repro.ts
Encoded TOON payload:
message: "Hello [world] this is a test:"

Decoded object:
{
  message: "Hello [world] this is a test:",
}

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Changes Made

• Added a check in parseArrayHeaderLine (packages/toon/src/decode/parser.ts) to ensure array header parsing is aborted if a key-value separator (:) appears before the first bracket ([).

SPEC Compliance

• This PR implements/fixes spec compliance
• Spec section(s) affected: Key-Value Pair Parsing
• Spec version: 3.3

Testing

• All existing tests pass
• Added new tests for changes
• Tests cover edge cases and spec compliance

Pre-submission Checklist

• My code follows the project's coding standards
• I have run code formatting/linting tools
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation if needed
• I have reviewed the https://github.com/toon-format/spec for relevant sections

Breaking Changes

• No breaking changes
• Breaking changes (describe migration path below)

Additional Context

This issue was specifically encountered when attempting to parse TOON documents with titles containing translated bracket tags and source parentheses (e.g., doujinshi/gallery metadata).