Compiler: allow function calls on lazy state

[doc-han]

Short Description

Currently function calls on lazy-state do not work.
eg.

fn((state) => {
   state.callMeMaybe = () => {}
  return state
});
// does not work before this PR
fn($.callMeMaybe())

This is because, we fail to wrap the state callback well. This update fixes that.

How it worked before and after

Given the source code fn($.callMeMaybe())

Before this PR	After this PR
fn((state => state.callMeMaybe)())	fn(state => state.callMeMaybe())

Fixes #684

Implementation Details

Steps

1. after finding the MemberExpression with $, we start walking up the tree to find a CallExpression to wrap.
2. when we find this CallExpression, a simple check is done to find out whether the parent of this CallExpression is another CallExpression with callee being state. (that's how we know it's a function called on a lazy-state)
3. we then want to wrap the state stuff at an additional level up for it to work!

QA Notes

List any considerations/cases/advice for testing/QA here.

AI Usage

Please disclose how you've used AI in this work (it's cool, we just want to know!):

• Code generation (copilot but not intellisense)
• Learning or fact checking
• Strategy / design
• Optimisation / refactoring
• Translation / spellchecking / doc gen
• Other
• I have not used AI

You can read more details in our Responsible AI Policy

[doc-han]

@josephjclark I want to add a good runtime/cli test for this. where do you think would be best to add that.

fn((state) => {
    state.callMeMaybe = (value) => {
        state.greetings = `hello ${value}`
		return state; // crazy! seems every function body that does something with state has to return it
    }
    return state
});

fn(state => {
    state.name = "John"
    return state;
})

fn($.callMeMaybe($.name)) // note: if callMeMaybe doesn't return state, next operation wouldn't have state passed.

Then the value at state.greetings will be "hello John"

Note

We can say that. every function body that has something to do with state should return it.

[doc-han]

Note: I ignored the other example from #684

fn((state) => {
   $.callMeMaybe()
})

Because according to our discussion. that should be ILLEGAL!

[josephjclark]

every function body that has something to do with state should return it.

Uh, well not really. It depends on how it's used. We talk about Operations - a function which takes state and returns state. If you're using a function as an operation - then yeah, the function body must return state.

But I can re-write your code like this:

fn((state) => {
    state.callMeMaybe = (value) => {
        state.greetings = `hello ${value}`
    }
    return state
});

fn(state => {
    state.callMeMaybe(); // no need to return state in this case
    return state;
})

But I think you're hitting on something important. Since we can't use lazy state inside a callback, the use of this is limited.

If I do:

fn($.callMeMaybe($.name))

Then the function must indeed be an Operation.

We can do stuff like this though

fn((state) => {
  state.buildUrl = (resource) => `api/v1/${resource}`
  return state;
});
get($.buildUrl(resourceName))

But thinking this through is making me really de-value the utility of functions on state. I think it's just creating confusion.

#648 would be a much more useful facility (although the issue needs a lot of love!)

[josephjclark]

@doc-han let me think about this but this does feel low priority now 🤔 If it feels safe I'll merge it

[josephjclark]

Hiya @doc-han - I want to merge this even though I don't think it's very valuable in the end.

We have a suite of tests in integration-tests/execute which test the compiler and runtime on job code. This is quite new and we don't have many - but it's nice to be able to test job code without the overhead of the CLI (or indeed the multi-process worker engine).

Can I ask you to create a file called lazy-state.test.ts in there and add a few simple lazy state tests and then a test or two on this specifically?

Don't go too overboard - just plug in a nice starting point :)

Thanks!

[doc-han]

Can I ask you to create a file called lazy-state.test.ts in there and add a few simple lazy state tests and then a test or two on this specifically?

Done

[josephjclark]

Thanks @doc-han ! Appreciate it