jestjs/jest

Zero width chars not showing in diff

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#10584 opened on Oct 4, 2020

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 (12 comments) (0 reactions) (0 assignees)TypeScript (45,361 stars) (6,653 forks)batch import
:rocket: Feature RequestHelp WantedPinned

Description

🐛 Bug Report

Differences in strings containing zero width chars are not highlighted, making them incredibly hard to spot and debug. Eg, one of the following strings has as its first character (character at position 0) a byte order mark character as its first character, and the other has the letter "T" as its first character.

image

Additional useful info

To Reproduce

Just create two strings that look identical, one of which contains a character such as the BOM character.

Expected behavior

A clear indication of the difference.

envinfo

  System:
    OS: Linux 5.4 Ubuntu 18.04.5 LTS (Bionic Beaver)
    CPU: (8) x64 Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
  Binaries:
    Node: 14.4.0 - ~/.nvm/versions/node/v14.4.0/bin/node
    Yarn: 1.21.1 - /usr/bin/yarn
    npm: 6.14.5 - ~/.nvm/versions/node/v14.4.0/bin/npm
  npmPackages:
    jest: ^26.0.1 => 26.0.1

Contributor guide

Tech stack
typescriptnodejsjavascript
Domain
testingdeveloper experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic understanding of unicode charactersfamiliarity with Jest's diff logic
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Review the issue comments (12 total) and related issues #8448 and #6881 for discussion. The fix likely involves modifying the diff algorithm in `packages/expect utils/src/utils.ts` or similar to highlight zero width characters. Explore how the current diff handles invisible characters and consider using Unicode property escapes or character width detection. Look for any existing PRs or branches that attempt a fix.