Support optional keyword and other terraform 1.0 language enhancements

[samart]

Support optional keyword for variables.
recognize tomap and tolist functions

[VladRassokhin]

What is "optional keyword for variables"?
tomap and tolist supported in 0.7.11

[haidaraM]

optional experimental keyword is defined here: https://www.terraform.io/docs/language/expressions/type-constraints.html#experimental-optional-object-type-attributes.

There is also a defaults experimental function: https://www.terraform.io/docs/language/functions/defaults.html. Not sure if it's supported or not

[VladRassokhin]

Fixed optional in 0.7.14
defaults is somehow works.

[mrlexor]

Hello,

I've found out this closed issue regarding optional modifier. It's actually work, but not as expected.

Optional modifier has two arguments and if I use it only with as shown one, so linter shows that okay:

However, when I add the second one, default argument, linter, seems, doesn't know about it:

Can you take a look, please?

Here you may find information about default argument for the optional modifier.