Regression Bug: Error "The type of this node cannot be serialized because its property '[fooSymbol]' cannot be serialized." happens but potentially avoidable automatically.

[LumaKernel]

🔎 Search Terms

"symbol", "generics", "serialization", "module", "export", "degression"

🕗 Version & Regression Information

The main behaviour can be categorized in 3 kinds in recent versions. Recommended to read code example first.

• This changed between versions 4.7 and 4.8
  • But the details of its behaviour is continue to change subtly in next versions.
• I confirmed g1 and g2 both can be exported without an error in:
  • v4.7.4
  • v4.6.4
  • v4.5.5
• And both g1 and g2 cannot be exported in:
  • v4.8.4
  • v4.9.5
  • v5.0.4
  • v5.1.6
  • v5.2.2
  • v5.3.3
  • v5.4.5
• And only g2 can be exported without an error.
  • v5.5.4
  • v5.6.2

⏯ Playground Link

https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=2&pc=1#code/KYDwDg9gTgLgBAYwgOwM7wGYQgZQJ4C2ARhADZwC8c+xZAFAORYQMCUA3AFCiSxwx4wwOADFsNEuSoChEDHGYSyXbuGjwkaTJTgAeACpxQMYMgAmqOBCIArYAhgA+OhlIBDAOYAuOCTLA3ZFZKRzg6ADcfQwAyOABvOABtAGk4AEtkUXFCSQBdHwBXZABrZAgAd0yAX2CKUISAegAqOFQIAmFSCA80hEsmhrgqrgbBjwBGHwBRKChoKIALYRlhOX4FtMsys2EEQLL4ImFUYCg0t1I0gC9gM197NwKT9JhLMDmhWDw4BkTFHLIuQYiH2EEOx1O50uNzMADo6AAWcbjAAcrFUvA0KHQcAmOgMRhAJnMlmsdgczlqoQwBmcMCgBWAHAx6kQ2PgHgATPjDMZTBYrLZ7E46FSwpE4DF4klUhksrgAaR8nAiqUKtUxQlNDjXJ4dPTGew4M1Wu1Ot1ev1BsNOEA

💻 Code

export const fooSymbol = Symbol('foo');
export type FooSymbol = typeof fooSymbol;

export const f = <T extends object>(flag: boolean) => (v: T & { [K in FooSymbol]: unknown }) => { /* some logics */ };
// g1: Error: The type of this node cannot be serialized because its property '[fooSymbol]' cannot be serialized.(4118)
export const g1 = <T extends object>() => f<T>(true);
export const g2 = <T extends object>() => (v: T & { [K in FooSymbol]: unknown }) => { const flag = true; /* some logics */ };

🙁 Actual behavior

The function g1 seems correctly typed, exported, but error is shown as The type of this node cannot be serialized because its property '[fooSymbol]' cannot be serialized.(4118) by the compiler.
g1 is potentially rewritten in the form of g2, just directly rewrite the given arguments as local constant (or just embed values in all contexts).

🙂 Expected behavior

g1 is acceptable as well as g2.

Additional information about the issue

Generics usage is essential to reproduce this case. I'm not sure if the code example could be minimized.
It's the real case minimization of what I really needed in my projects.

[caeus]

Still happening in 5.9.2 in similar cases, but only if compilerOptions.declararion is set to true

[Voltra]

In my case, in 5.9.3, I get that error even when compilerOptions.declaration is not set (or explicitly set to false).

It looks like it's trying to "serialize" an array/tuple type as an object (with its methods as properties, etc.) instead of treating it as an array/tuple.

TS4118: The type of this node cannot be serialized because its property [iterator] cannot be serialized.

TS4118: The type of this node cannot be serialized because its property [unscopables] cannot be serialized.

These warnings come from trying to "serialize" the type of the deeply nested property below from an as const object (needed for inference):

export const DATA = {
  // [...]
  {
    "enum": [
        0,
        1,
        2
    ],
    "type": "number",
  },
  // [...]
};

export default DATA;

Same with with:

export const DATA = {
  // [...]
 {
    "required": [
          "id",
          "items",
          "name",
          "status"
      ],
      "type": "object"
  },
  // [...]
};

export default DATA;