Svelte: Throw a warning if we are declaring a variable with const and also using bind directive to mutate its value.

[kanishk30]

Is your feature request related to a problem? Please describe.
While defining a variable in #Svelte, make sure to use let/var and not const, otherwise those bindings won't work, as it can't be updated by its compiler.

Describe the solution you'd like
Throw a warning or error.

Describe alternatives you've considered
Using let always.

How important is this feature to you?
It brings a delight to users.

[Conduitry]

This sounds reasonable. I think I'd favor an outright compilation error in this case. We need to be careful though because binding to foo.bar when foo is a const should continue to be valid.

[kanishk30]

Yes absolutely. Making sure that primitives cannot be mutated once assigned with const. Sounds reasonable?

[tanhauhau]

Some pointers for getting started on the good first issue:

1. Read our Contribution Guide
2. We checked whether the bind: variable is defined or not here in src/compiler/compile/nodes/Binding.ts
   
   
   
   • You can add another check to see whether the variable can be mutated.
   
   
   • Exhaustive list of the properties of the variables can be found in the vars section of the doc
   
   
3. tests for compile time validation goes into the test/validator/ folder (you can refer to this test sample)

[vlasy]

I am working on this. I already have a working implementation, but need to fix some tests.

[kanishk30]

sure @vlasy . Was planning to pick it up this weekend.