Handle abstract types in type checking

[schorg]

Describe the todo When compiling signatures, abstract types are not handled.

module exposes init

struct S 
    var x: bool
end

function init() returns S 
    return {x = true}
end

gets signature

signature

@[ComplexType]
type S

function init() returns S

type S is currently not handled by the typechecker. Attributes @[ComplexType] and @[SimpleType] are currently not handled by the attribute checker.

Link to a branch Typechecking and attribute checking codegeneration for feature/modules Testcase

Task list To mark completed todos, use [x]

• [x] Complete type checking for abstract types
• [x] Complete attribute checking for abstract types
• [x] Write some test cases

[FriedrichGretz]

The type checker now does check annotations for opaque types and checks initialisation of opaque typed variables.

However, export inference is not checked. Can we ensure that, e.g.

• an implicitly exported simple type is correctly identified as "simple opaque" by the inference checker

[schorg]

Yes we can.

The import compilation for export inference only runs the phases before the type checker and then generates the signature.

I added a valid test case to the export inference tests. Just run the test: exportinference/valid/useabstractsimple.blc and inspect the generated signature in: exportinference/imports/abstractsimple.blh