Show key type info when hovering over an index lookup on TypedDicts

[R-O-C-K-E-T]

Current Behaviour

When hovering over an index operation into a TypedDict variable no type info for the key appears and definition is unavailable.

In contrast constructing a TypedDict object hovering over keys there does produce type info and definition.

from typing import TypedDict

class Test(TypedDict):
    field: str

test: Test = {
    'field': 'value',  # Hovering over 'field' gives type info and the definition is available
}
test['field']  # Hovering over 'field' in this case gives no info and no definition is found

Expected Behaviour

Hovering over a TypedDict key within an indexing operation should show the key type info and the definition should be available.

Motivating Use Case

Plain dictionaries often appear in legacy code bases and when migrating types into these code bases it is easier and less error prone to write TypedDicts to describe these dictionaries instead of migrating them into dataclasses or similar (IMO). Which do show type info when hovering over the property names.

Migrating this way works well to verify that all accesses and definitions are valid. However when writing code that indexes into one of these dictionaries, finding either the type, docstring or definition of a key is cumbersome. Since the developer must find the type of the indexed object the and manually scan through to the relevant key.

Future Ideas

Hover/Definition search for TypedDict.get

.get is often used when keys are marked NotRequired to skip verbose 'key' in obj checks. It may improve usability if key definitions were easily available.

from typing import TypedDict, NotRequired

class Test(TypedDict):
    field: NotRequired[str]

test: Test = {}
test.get('field')  # Hovering over 'field' could show type info for the 'field' key

Hover/Definition search for NamedTuple indexing

The same functionality for TypedDict could be applied to NamedTuple. The use case is weaker however, since the field can be directly referenced by name instead of by index.

from typing import NamedTuple

class Test(NamedTuple):
	first: int
	second: str

test = Test(1, 'second')
res = test[1]  # Hovering over 1 could show type info for the 'second' key

[erictraut]

The hover provider shows the types of identifiers in your code. It doesn't do anything for a string literal because the type of that string literal is, well, a str. I suppose it could treat string literals specially if they are used to index a TypedDict, but that would be a special case and somewhat inconsistent.

In any case, I will transfer this request to the pylance-release project since it relates to a language server feature. The pylance team can decide whether to pursue this enhancement request or wait for additional feedback from pylance users.

@rchiodo or @debonte, could you transfer this to pylance-release? Thanks!

[debonte]

Moving this issue to discussion as an enhancement request for comments and upvotes.