Suggestion: noInferredAny

Search Terms

noImplicitAny inference any noInferredAny

Suggestion

Symbols typed as any reduce the type safety of a program. That's fair if the programmer intended to use any. However it's relatively easy to end up with symbols typed any through type inference chains that are not obvious:

• 3rd party libraries might return any
• complex type expressions might infer to any
• some .d.ts types default generic arguments to any (e.g. Set)

In all these situations, a programmer might write const foo = something(); and expect foo to have a reasonable inferred type. foo being inferred to any is easy to miss in such code, both while editing and while reviewing code.

Proposal: add a compiler option noInferredAny that flags symbols whose type is any and that do not have an explicit type annotation.

Use Cases

• better type safety for programs
• detect weak typings in your dependencies
• more

Examples

const foo1 = returnsAny();  // error
const foo2: any = returnsAny(); // ok
const foo3: string = returnsAny(); // probably ok, programmer gave an explicit type? could also require an explicit cast.
const foo4 = returnsAny() as string;  // ok

const {foo5}: {foo5: string} = returnsAny(); // ok

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Empieza por la propuesta y sus ejemplos, especialmente por la distinción entre any inferido y any anotado explícitamente. Revisa los casos de inferencia enumerados y define cómo debe comportarse la opción en cada uno; el trabajo estará terminado cuando el compilador pueda marcar de forma coherente los símbolos sin anotación inferidos como any sin cambiar el JavaScript emitido.