The return value of function type is not checked when function may return any

**TypeScript Version:** 4.2.0-dev.20201124 **Search Terms:** function, type check, any **Code** ```ts const f1: () => number = () => { if (window) { return {} as any; } return "a"; // Pass }; // Expected behavior const f2: () => number = () => { return "a"; // Error: Type '() => string' is not assignable to type '() => number' }; // Expected behavior function f3(): number { if (window) { return {} as any; } return "a"; // Error: Type 'string' is not assignable to type 'number'. }; ``` **Expected behavior:** `f1` causes an error because it returns a string. **Actual behavior:** `f1` does not cause an error. **Playground Link:** <!-- A link to a TypeScript Playground "Share" link which demonstrates this behavior --> https://www.typescriptlang.org/play?ts=4.2.0-dev.20201124#code/MYewdgzgLgBAZgRgFwwBQEoYF4B8MwCuAtgEYCmATtmprjAN4BQMMAlnGgO6tgAmInTExYsKZKAQpgGAXxgBDCArABPANzMYMzWIlSYAInkG1MAPRmYABUURGMjYwswAogA8ADmWBQyvGOQAFvIAbqwgFIygkLBwAEwoGNh4hKSU1El0wjC6ktJGJuaWLhQUESgAKipeMADkmXjQFDwA5rVsSmAgsLasLWDyJAA2ZDBQIGPVo-W0KcTkFLX2js7uXj5+AWTBYRGMcARgPuHScADMGCipCwya7Fw8-IK3IjniebIKSvKqGizaone+gKplWpXKMCqNVqTVa7VYnW6XwgfQGw1G40m0OulFqADplowgA