Surface reportAttributeAccessIssue even when type checking mode set to off

[luabud]

This is from a convo with @DanielRosenwasser about this suggestion: microsoft/pyright#7579
He brought up a good point that it seems to be a pretty common mistake to try to access TypedDict attributes using . instead of [""]. For example:

from typing import TypedDict

class Person(TypedDict):
    name: str

def func(p: Person):
    print(p.name) ## ---> should be p["name"]

It'd be nice if we could surface a diagnostic even when type checking mode is set to off to help users catch this error sooner, as many times it may cause a run time error. He suggested we could surface it as a suggestion diagnostic too, which I think it's a good idea if we believe error would be too intrusive.

We'd probably get bonus points for surfacing a "Fix code spelling" code action to translate from .key to ["key"] :)

[erictraut]

it seems to be a pretty common mistake

Do we have evidence of this statement, or is this just conjecture? I suspect this mistake is more common for someone coming from TypeScript, but I'm guessing that it's much more rare for Python programmers. Also, if someone is using TypedDict in their code, they are much more likely to have type checking enabled (at least in basic mode). Most Python programs don't use TypedDict and instead just use regular dict classes.

I'd be reluctant to create a separate diagnostic category that is particular to this very specific error case.

[DanielRosenwasser]

It's probably better to focus less on the specific error message being discussed and more broadly on where suggestion diagnostics can be applied.

In TypeScript, we issue suggestion diagnostics in unchecked JavaScript files for several error messages. I briefly called it out in microsoft/pyright#7579.

A couple of example errors that get surfaced as suggestion diagnostics include:

1. Misspelled local bindings
2. Misspelled properties/attributes
3. Unnecessary await (which I believe is actually a hard error in Python?)

For Pylance, the first one already has a quick fix in the language service (though the error message doesn't mention any suggestion). The next two don't have any fixes.

Related:

• Provide high-confidence spelling suggestions as suggestion diagnostics TypeScript#41582
• Provide Grammar Errors for JavaScript Files TypeScript#45349