Type intersection is not detected as empty through generics

[fefrei]

TypeScript Version: 3.7.5

Search Terms: union intersection type conflict empty inference generics

Expected behavior:

TypeScript can determine when type intersections are empty. For example,

const t1 = (t: "a" | ("b" & "c")): "a" => t;
const t2 = (t: number | ("b" & "c")): number => t;

is perfectly valid. This is very useful, and it even works through generics:

type Container<Type extends string> = {
    type: Type;
}

const t3 = (t: Container<"a"> | (Container<"b"> & { dataB: boolean } & Container<"a">)): Container<"a"> => t;

I'd expect t3 to be validly typed even when the left side of the union and the return type are changed to another type, like so:

const t4 = (t: number | (Container<"b"> & { dataB: boolean } & Container<"a">)): number => t;

Actual behavior:

However, this is a type error:

Type 'number | (Container<"b"> & { dataB: boolean; } & Container<"a">)' is not assignable to type 'number'.

You can find context for where this is relevant here on Stack Overflow, or in this playground.

Related Issues: None found.

Code

const t1 = (t: "a" | ("b" & "c")): "a" => t;

type Container<Type extends string> = {
    type: Type;
}

const t2 = (t: Container<"a"> | (Container<"b"> & Container<"c">)): Container<"a"> => t;
const t3 = (t: Container<"a"> | (Container<"b"> & { dataB: boolean } & Container<"a">)): Container<"a"> => t;
const t4 = (t: number | (Container<"b"> & { dataB: boolean } & Container<"a">)): number => t;

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided