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This PR updates our call binding logic to handle splatted arguments. Complicating matters is that we have separated call bind analysis into two phases: parameter matching and type checking. Parameter matching looks at the arity of the function signature and call site, and assigns arguments to parameters. Importantly, we don't yet know the type of each argument! This is needed so that we can decide whether to infer the type of each argument as a type form or value form, depending on the requirements of the parameter that the argument was matched to. This is an issue when splatting an argument, since we need to know how many elements the splatted argument contains to know how many positional parameters to match it against. And to know how many elements the splatted argument has, we need to know its type. To get around this, we now make the assumption that splatted arguments can only be used with value-form parameters. (If you end up splatting an argument into a type-form parameter, we will silently pass in its value-form type instead.) That allows us to preemptively infer the (value-form) type of any splatted argument, so that we have its arity available during parameter matching. We defer inference of non-splatted arguments until after parameter matching has finished, as before. We reuse a lot of the new tuple machinery to make this happen — in particular resizing the tuple spec representing the number of arguments passed in with the tuple length representing the number of parameters the splat was matched with. This work also shows that we might need to change how we are performing argument expansion during overload resolution. At the moment, when we expand parameters, we assume that each argument will still be matched to the same parameters as before, and only retry the type-checking phase. With splatted arguments, this is no longer the case, since the inferred arity of each union element might be different than the arity of the union as a whole, which can affect how many parameters the splatted argument is matched to. See the regression test case in `mdtest/call/function.md` for more details. |
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| .. | ||
| corpus | ||
| mdtest | ||
| primer | ||
| README.md | ||
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/ty_test/README.md for documentation of this test format.