feat(transformer): Support overloaded functions by attaching signatures on use - #390
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…es on use
Add overloads feature flag that enables this feature.
Enabling it makes the transformer process function calls if their declaration
was previously marked for mocking (via getMethod).
From a type-perspective, typed methods shouldn't bother to consider their inputs
in order to determine the output in runtime. At transformation time, the type
checker resolves the matching overload and that information can be used to
attach to the function, by utilizing the "instance" (`this`) of it. The
transformer changes transform functions in the following way.
```
mockedFunction() -> mockedFunction.apply(<signature>, [])
```
As for constructor instantiation signatures in interfaces, those can be wrapped
by an intermediate function that will copy the mocked properties to preserve the
instantiation behavior.
```
new mockedNewFunction()
|
`-> new (mockedNewFunction[<signature>] || (mockedNewFunction[<signature>] = function() {
Object.assign(this, mockedNewFunction.apply(<signature>, []));
}))()
```
These attached interfaces will determine the branching at runtime and to reduce
as much overhead as possible, all signatures of an overloaded function are
mapped to the resolved return type and stored in a jump table, i.e.:
```
getMethod("functionName", function () {
const jt = {
['<signature-1>']: () => <signature-1-return-descriptor>,
['<signature-2>']: () => <signature-2-return-descriptor>,
...
};
return jt[this]();
})
```
It should be noted, that if spies are introduced using the method provider, then
`this` will be occupied by the signature key.
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Add overloads feature flag that enables this feature.
Enabling it makes the transformer process function calls if their declaration
was previously marked for mocking (via getMethod).
From a type-perspective, typed methods shouldn't bother to consider their inputs
in order to determine the output in runtime. At transformation time, the type
checker resolves the matching overload and that information can be used to
attach to the function, by utilizing the "instance" (
this) of it. Thetransformer changes transform functions in the following way.
As for constructor instantiation signatures in interfaces, those can be wrapped
by an intermediate function that will copy the mocked properties to preserve the
instantiation behavior.
These attached interfaces will determine the branching at runtime and to reduce
as much overhead as possible, all signatures of an overloaded function are
mapped to the resolved return type and stored in a jump table, i.e.:
It should be noted, that if spies are introduced using the method provider, then
thiswill be occupied by the signature key.This is an alternative implementation of the feature(s) covered in #303 and #313