Compiler crash: Debug Failure in visitEachChildOfIndexSignatureDeclaration

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### 🔎 Search Terms

typescript debug failure index signature
visitEachChildOfIndexSignatureDeclaration
typescript compiler crash decorator addInitializer
invalid index signature decorator
typescript Debug Failure index signature

### 🕗 Version & Regression Information

- This is the behavior in the version I tested (TypeScript 5.9.3). I reviewed the FAQ and did not find entries related to this compiler crash.

### ⏯ Playground Link

https://www.typescriptlang.org/play/?#code/FAMwrgdgxgLglgewgAgIYGd1wgcwCoCeADgKYAUIEAXMgGKSyIQA0yA+rAB40DCANhnQBZEjAAWCACYARElAQAnVDEU8kMEpxgBKAN7BkyA8j6jklAHKoAtiWQBedlwB0EGyWDGOMTs9STJAEkIOHhUPjgALxIFCgZ4JDJxOHQaXQBtAGsSAhp0GAVsHABdVlQIAgBfbWR9Q3rkZPR0y3dnFQBlAqKybWKHcwhnACNsSSSxFO0AbmNq42MFUTAFFHBoBJQAdyUiUgVkCZSacoJmZwvUBRxUtArkGpoANwQ4STr6+Qh0BFNnPgQODIAAMoAJMMhbOIpJD3MgACS6Vq2doILqFXC9SrA7TGQyUZxQcJ8I7oVgXPzXdC4wyVTyVIzAMGCZAACRIfABtWMX3yCjAsEUvX0cwWhgAAoIioRSMZJGiEFCiodtM9Xu88cheb8SP9AWQAERiDkAg005B0ypAA

### 💻 Code

```typescript
function assingType(fn: Function, _ctx: ClassMethodDecoratorContext){

let fnName = _ctx.name

_ctx.addInitializer(function(this: {[key: string], any}) { // here is my sintaxis error
// Invalid type annotation. The compiler should report a type error,
// but instead it crashes with "Debug Failure".
this[fnName.toString()] = fn.bind(this);
})

return function wrapper (this: any,...args: any ) : void{
console.log(`class method mame ${fnName.toString()}`)
fn.call(this, ...args)
}

}

class Hello {
constructor(){

}

@assingType
doSometing (): void{
console.log("hello")
}
}

```

### 🙁 Actual behavior

C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:123168
throw e;
^

Error: Debug Failure.
at visitEachChildOfIndexSignatureDeclaration (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90865:13)
at visitEachChild (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90721:33)
at visitEachChild2 (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:133010:16)
at visitExistingNodeTreeSymbolsWorker (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:132899:23)
at visitExistingNodeTreeSymbols (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:132658:22)
at visitArrayWorker (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90535:49)
at visitNodes2 (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90506:19)
at visitEachChildOfTypeLiteralNode (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90911:7)
at visitEachChild (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:90721:33)
at visitEachChild2 (C:\Users\diazc\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:133010:16)

### 🙂 Expected behavior

The TypeScript compiler should not crash.

If the code is invalid, the compiler should emit a normal type error instead of throwing a "Debug Failure" during compilation.

### Additional information about the issue

This code does not crash in the TypeScript Playground. The Playground only reports normal type-checking errors.

However, when compiling locally with `tsc` (TypeScript 5.9.3), the compiler crashes with a "Debug Failure" during compilation.

A screenshot of the stack trace from the local `tsc` execution is attached.

Inizia con il codice TypeScript fornito e riproduci localmente il crash con tsc 5.9.3, quindi confrontalo con il risultato del Playground. Traccia lo stack a partire da visitEachChildOfIndexSignatureDeclaration e usa l'annotazione della firma di indice non valida come caso di riferimento. Il lavoro è completo quando il compilatore segnala un normale errore di tipo invece di generare Debug Failure.

Scritto dal modello di indicizzazione a partire dal testo della issue.