TSGO not reporting TS2548

[Titozzz]

Steps to reproduce

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBANiOMC8MDaA6LAKMBXOJAQwhjzAGswQB3MGEsy6utAXRgB8Z9CBKNgG4AUEA

Behavior with typescript@5.9

test.ts:13:7 - error TS6133: 'lol' is declared but its value is never read.

13 const lol = [...(null as unknown as unknown[] | null)];
         ~~~

test.ts:13:17 - error TS2548: Type 'unknown[] | null' is not an array type or does not have a '[Symbol.iterator]()' method that returns an iterator.

13 const lol = [...(null as unknown as unknown[] | null)];
                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 2 errors

Behavior with tsgo

test.ts:13:7 - error TS6133: 'lol' is declared but its value is never read.

13 const lol = [...(null as unknown as unknown[] | null)];
         ~~~


Found 1 error

[ahejlsberg]

I can't reproduce this behavior. Here's what I'm seeing with your one-line repro:

c:\tc\test>tsgo
t.ts:1:17 - error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.

1 const lol = [...(null as unknown as unknown[] | null)];
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 1 error in t.ts:1

c:\tc\test>tsc
t.ts:1:17 - error TS2488: Type 'unknown[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.

1 const lol = [...(null as unknown as unknown[] | null)];
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 1 error in t.ts:1

[ahejlsberg]

And here's what I'm seeing with noUnusedLocals: true:

c:\tc\test>tsgo
t.ts:1:7 - error TS6133: 'lol' is declared but its value is never read.

1 const lol = [...(null as unknown as unknown[] | null)];
        ~~~

t.ts:1:17 - error TS2488: Type 'null' must have a '[Symbol.iterator]()' method that returns an iterator.

1 const lol = [...(null as unknown as unknown[] | null)];
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 2 errors in the same file, starting at: t.ts:1


c:\tc\test>tsc
t.ts:1:7 - error TS6133: 'lol' is declared but its value is never read.

1 const lol = [...(null as unknown as unknown[] | null)];
        ~~~

t.ts:1:17 - error TS2488: Type 'unknown[] | null' must have a '[Symbol.iterator]()' method that returns an iterator.

1 const lol = [...(null as unknown as unknown[] | null)];
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 2 errors in the same file, starting at: t.ts:1

[Titozzz]

I'll try to either narrow it down to a small reproduction, or, find what causes my issue and will be back to you.