Warn when regular expression is used in conditional

🔍 Search Terms

• conditional
• regular expression
• regex

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

When a regular expression literal appears in a conditional, such as:

if (/abc?/) {
    foo()
} else {
    bar()
}

It would be helpful warn that bar() is unreachable. The programmer likely meant to call /abc?/.test(...)

TypeScript could help catch this easy to make mistake

📃 Motivating Example

We recently were bitten by this in VS Code. It slipped through code review too

💻 Use Cases

Help programmers catch an easy to make mistake

Es werden keine Dateien, Tests oder Einstiegspunkte genannt. Beginne damit, die Diagnosen für bedingte Ausdrücke in TypeScript und bestehende Prüfungen auf unerreichbaren Code zu finden; als erledigt gilt die Aufgabe, wenn Literale regulärer Ausdrücke in Bedingungen eine Warnung erzeugen, ohne das ausgegebene JavaScript zu ändern, mit einer Abdeckung für den gezeigten if/else-Fall.