Crash: Debug Failure. type must be class or interface in getBaseTypes triggered by invalid optional rest parameter in Constructor type

[na7ure-a]

🔎 Search Terms

"Debug Failure. type must be class or interface"

"Rest parameter cannot be optional crash"

"isConstructorAccessible crash strict mode"

"Mixin protected constructor crash"

🕗 Version & Regression Information

Versions tested: 5.7.3, 5.8.3, 5.9.3, Nightly

Behavior: All tested versions crash when --strict is enabled.

Condition: The crash only occurs when --strict is used. Without --strict, the compiler correctly identifies the syntax error (TS1047) and the semantic error (TS2674).

⏯ Playground Link

https://www.typescriptlang.org/zh/play/?target=7&ts=6.0.0-dev.20251222#code/MYGwhgzhAECCBGEAuAnMwnQN4FgBQ0h0ADigPZICmGlAJtMGQHbIoCuGZKAFAJTb4i0AL75ReUJBgBhZsBSUq0SgA8qTWjASt0mXHnFIAnsUrRZLVByRcAPABVoAXmzCAfM+hNKAd2jcAOiCwFABzCAB+AC5oMCYjAG0AXX4nD3sAbnwAMzYmDABLZmgAWQKVAqYHACFIM1V1TXNmVmsuN25aiEoY+y7Kfn0hBSQ2FCYGcChlNUoNGH6BAiJhLIN8SWmAUQBbYmMl8U2ZNAgAC3sUAtDQyhQZxpgyiqZuXf2jQcEiYjZ4EAKwGgqGutx4X2WQkI3j8FnkikofDWQnEwiAA

💻 Code

class Abstract {
    protected constructor() {
    }
}
class Concrete extends Abstract {
}
type Constructor<T = {}> = new (...args?: any[]) => T;
function Mixin<TBase extends Constructor>(Base: TBase) {
    return class extends Base {
    };
}
class Empty {
}
class CrashTrigger extends Mixin(Empty) {
    public trigger() {
        new Concrete();
    }
}

🙁 Actual behavior

.\ts-versions\nightly\node_modules\.bin\tsc.cmd  --ignoreConfig --strict  .\bugfind\2\noCrashOnMixin_m.ts
D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:123191
     throw e;
     ^

Error: Debug Failure. type must be class or interface
   at getBaseTypes (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:57088:17)                                                                                                     
   at typeHasProtectedAccessibleBase (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:76955:23)                                                                                   
   at typeHasProtectedAccessibleBase (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:76982:12)                                                                                   
   at typeHasProtectedAccessibleBase (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:76982:12)                                                                                   
   at isConstructorAccessible (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:76999:13)                                                                                          
   at resolveNewExpression (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:76918:12)                                                                                             
   at resolveSignature (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:77323:16)                                                                                                 
   at getResolvedSignature (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:77348:20)                                                                                             
   at checkCallExpression (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:77456:23)                                                                                              
   at checkExpressionWorker (D:\do\tscFuzz\ts-versions\nightly\node_modules\typescript\lib\_tsc.js:80921:16)   

.\ts-versions\nightly\node_modules\.bin\tsc.cmd  --ignoreConfig   .\bugfind\2\noCrashOnMixin_m.ts        
bugfind/2/noCrashOnMixin_mutated_17.ts:7:40 - error TS1047: A rest parameter cannot be optional.

7 type Constructor<T = {}> = new (...args?: any[]) => T;
                                        ~                                                                                                                                                               

bugfind/2/noCrashOnMixin_mutated_17.ts:16:9 - error TS2674: Constructor of class 'Abstract' is protected and only accessible within the class declaration.

16         new Concrete();
          ~~~~~~~~~~~~~~                                                                                                                                                                                
Found 2 errors in the same file, starting at: bugfind/2/noCrashOnMixin_mutated_17.ts:7  

🙂 Expected behavior

The compiler should not crash. It should report the existing errors normally:

error TS1047: A rest parameter cannot be optional.

error TS2674: Constructor of class 'Abstract' is protected and only accessible within the class declaration.

Additional information about the issue

No response