Generate argument number checks for JS code

[CrescentonC]

I modified JSBuilder.scala such that now three places related to function/method codegen call the method handleFunction to handle the common logic. The handleFunction is overridden in JSBackendDiffMaker.scala such that argument number sanity checks are implemented using varargs in javascript.

I checked and also learned that in javascript arguments.length can also be used to determine how many arguments are actually passed into a function, but we generate arrow functions which do not have arguments.

[LPTK]

Nicely done, thanks! But please address my comments.

[CrescentonC]

Thanks for the comments! I have made the changes except for the one that makes sanity checks default, because currently several tests have function calls with incorrect number of arguments, but without :re. Should I make the change to add :re to them and make sanity checks default?

Also previously I use const x = args[i] to assign arguments values from varargs, but I just saw #238 and realize that arguments can be mutated, so I change to use let.

[LPTK]

currently several tests have function calls with incorrect number of arguments, but without :re. Should I make the change to add :re to them

Well, most are probably actual mistakes! Unless the intent was clearly to test what happens when the wrong number of arguments is passed, please just fix them by passing the correct number of arguments!

[CrescentonC]

Thanks for the comments! I have removed the val, and made the following changes to the tests and made sanity check on by default.

• add an :re at line58 in ClassInFun.mls
• add missing parameters at around line120 in IfThenElse.mls
• add an :re at line40 in Juxtapositions.mls
• add a :fixme at line 170 in Juxtapositions.mls

[LPTK]

Great! Just one last touch. And the errors would be more helpful if they had the following format:

Function 'foo' expected 3 arguments but got 2.