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[CS2] Output ES2015 arrow functions, default parameters, rest paramet…
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…ers (#4311)

* Eliminate wrapper around “bound” (arrow) functions; output `=>` for such functions

* Remove irrelevant (and breaking) tests

* Minor cleanup

* When a function parameter is a splat (i.e., it uses the ES2015 rest parameter syntax) output that parameter as ES2015

* Rearrange function parameters when one of the parameters is a splat and isn’t the last parameter (very WIP)

* Handle params like `@param`, adding assignment expressions for them when they appear; ensure splat parameter is last

* Add parameter names (not a text like `'\nValue IdentifierLiteral: a'`) to the scope, so that parameters can’t be deleted; move body-related lines together; more explanation of what’s going on

* For parameters with a default value, correctly add the parameter name to the function scope

* Handle expansions in function parameters: when an expansion is found, set the parameters to only be the original parameters left of the expansion, then an `...args` parameter; and in the function body define variables for the parameters to the right of the expansion, including setting default values

* Handle splat parameters the same way we handle expansions: if a splat parameter is found, it becomes the last parameter in the function definition, and all following parameters get declared in the function body. Fix the splat/rest parameter values after the post-splat parameters have been extracted from it. Clean up `Code.compileNode` so that we loop through the parameters only once, and we create all expressions using calls like `new IdentifierLiteral` rather than `@makeCode`.

* Fix parameter name when a parameter is a splat attached to `this` (e.g. `@param...`)

* Rather than assigning post-splat parameters based on index, use slice; passes test “Functions with splats being called with too few arguments”

* Dial back our w00t indentation

* Better parsing of parameter names (WIP)

* Refactor processing of splat/expansion parameters

* Fix assignment of default parameters for parameters that come after a splat

* Better check for whether a param is attached to `this`

* More understandable variable names

* For parameters after a splat or expansion, assign them similar to the 1.x destructuring method of using `arguments`, except only concern ourselves with the post-splat parameters instead of all parameters; and use the splat/expansion parameter name, since `arguments` in ES fat arrow functions refers to the parent function’s `arguments` rather than the fat arrow function’s arguments/parameters

* Don’t add unnamed parameters (like `[]` as a parameter) to the function scope

* Disallow multiple splat/expansion parameters in function definitions; disallow lone expansion parameters

* Fix `this` params not getting assigned if the parameter is after a splat parameter

* Allow names of function parameters attached to `this` to be reserved words

* Always add a statement to the function body defining a variable with its default value, if it has one, if the variable `== null`; this covers the case when ES doesn’t apply the default value when `null` is passed in as a value, but CoffeeScript expects `null` and `undefined` to act interchangeably

* Aftermath of having both `undefined` and `null` trigger the use of default values for parameters with default values

* More careful parsing of destructured parameters

* Fall back to processing destructured parameters in the function body, to account for `this` or default values within destructured objects

* Clean up comments

* Restore new bare function test, minus the arrow function part of it

* Test that bound/arrow functions aren’t overwriting the `arguments` object, which should refer to the parent scope’s `arguments` (like `this`)

* Follow ES2015 spec for parameter default values: `null` gets assigned as as `null`, not the default value

* Mimic ES default parameters behavior for parameters after a splat or expansion parameter

* Bound functions cannot be generators: remove no-longer-relevant test, add check to throw error if `yield` appears inside a bound (arrow) function

* Error for bound generator functions should underline the `yield`
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GeoffreyBooth authored Oct 26, 2016
1 parent c04c385 commit fb2be8e
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