feat: Infer the type for attributes from the assigned value with mypy

[Masara]

Is your feature request related to a problem?

Attributes, parameters and results in stubs, which are generated from python code, currently have no type information if the python code did not have type hints. Example:

# Python Code
class A:
    attr1: int
    attr2 = 2

    def my_func(a = 1):
        return a

// Safe-DS stubs
class A() {
    attr1: Int
    attr2

    fun myFunc(a = 1) -> result1: Any
}    

Furthermore, currently, if a function has no return type specified, the API will generate "Any" as the return type. This value has to be removed and the type has to be either inferred with mypy or left empty.

Desired solution

The API Class has to be adjusted to also infer type information with mypy if no type hints are given.
Then the following should be done:

1. Try to infer the type from the assigned value if mypy offers this functionality.

// Safe-DS stubs
class A() {
    attr1: Int
    attr2: Int

    fun myFunc(a: Int = 1) -> result1: Int
}    

2. If this is not possible (in general or for a specific case) add a TODO.

// Safe-DS stubs
class A() {
    attr1: Int
    // TODO Attribute has no type information.
    attr2

    // TODO Parameter has no type information.
    // TODO Result has no type information.
    fun myFunc(a) -> result1
}    

[Masara]

@lars-reimann Do we also want to infer parameter and result types?

[lars-reimann]

Yes to both. Later we can compare this with the information in the documentation.

[Masara]

@lars-reimann

1. For parameter default values and type hint, what kind of values do we support in Safe-DS? You once told me that we only support float, int, bool, str and None. Should I therefore ignore other types?
2. Mypy can't infer default values of attributes in init methods. Should I add "Type hint missing ..." todo messages none the less?

[lars-reimann]

1. For parameter default values and type hint, what kind of values do we support in Safe-DS? You once told me that we only support float, int, bool, str and None. Should I therefore ignore other types?

Default values can be any expression. Types can be any core class or any type for which you created stubs (i.e. a type defined in the library you create stubs for).

2. Mypy can't infer default values of attributes in init methods. Should I add "Type hint missing ..." todo messages none the less?

Yes, and leave the type empty.

[Masara]

@lars-reimann If we have a function like this:

def func(self):
    if ...:
        return 42
    elif ...:
        return False
    else:
        return 1.2, "some string"

how would the result information for the stubs look like?

[Masara]

@lars-reimann Would it be

fun func() -> (result1: union<Int, Boolean, Float>, result2: String?)

?

[lars-reimann]

For result1, we could set the type to:

• Any (common supertype of the possible types in the union)
• union<Int, Boolean, Float>
• literal<42, false, 1.2> (the exact possible values)

For now, I don't have a clear preference towards either option. Do whatever is easiest with mypy.

[Masara]

This issue is finished. This is a summary of some things, that Mypy could not handle:

1. Mypy can't infer default values of attributes in init methods.
2. Mypy can't infer the default value if its a call expression like some_attr = SomeClass()