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Hover type assertions

This document tests the hover assertion functionality in mdtest. Hover assertions allow testing the inferred type at a specific position in the code, similar to how a language server's hover feature works.

Basic hover assertions

The # ↓ hover: syntax lets us assert the type at a specific column position. The down arrow (↓) indicates the column where we want to check the type.

def test_basic_types(parameter: int) -> None:
    # ↓ hover: int
    parameter

    #        ↓ hover: Literal[10]
    number = 10

    #      ↓ hover: Literal["hello"]
    text = "hello"

Hovering on different expression types

Literals

#           ↓ hover: Literal[42]
int_value = 42

#              ↓ hover: Literal["test"]
string_value = "test"

#            ↓ hover: Literal[True]
bool_value = True

Names and attributes

class MyClass:
    value: int

def test_attributes(instance: MyClass) -> None:
    # ↓ hover: MyClass
    instance

    #        ↓ hover: int
    instance.value

Function definitions

def f(x: int) -> None: ...

#        ↓ hover: def f(x: int) -> None
result = f

Binary operations

#        ↓ hover: Literal[10]
#             ↓ hover: Literal[20]
result = 10 + 20

Comprehensions

# List comprehension
#        ↓ hover: list[@Todo(list comprehension element type)]
result = [x for x in range(5)]

Edge cases

Multiple hovers on the same line

We can have multiple hover assertions for different positions on the same line:

#       ↓ hover: Literal[1]
#           ↓ hover: Literal[2]
#               ↓ hover: Literal[3]
total = 1 + 2 + 3

#            ↓ hover: Literal[5]
#               ↓ hover: Literal[3]
result = max(5, 3)

Hovering works on every character in expression

def _(param: bool) -> None:
    #        ↓ hover: bool
    #         ↓ hover: bool
    #          ↓ hover: bool
    #           ↓ hover: bool
    #            ↓ hover: bool
    result = param

Hovering with unicode characters

def _(café: str) -> None:
    #        ↓ hover: str
    #         ↓ hover: str
    #          ↓ hover: str
    #           ↓ hover: str
    result = café

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