feature: add constant declarations

[b1ek]

i've added support for the const X = Y expression itself. it will resolve to declare -r X=Y, for both local and global variables, since declare -r is the same for locals as well

i also set args in main(args) to be constant. function parameters are never constant.

i don't know which is the minimal bash version for declare -r

[b1ek]

i just checked, declare -r works for bash 4.0:

[Ph0enixKM]

The reason why I never introduces const is because sh does not support it. So for instance on ash it fails:

[Ph0enixKM]

When we start to support sh - we should compile it to the regular variable instead (but still never let reassign the variable in the script)

[b1ek]

When we start to support sh - we should compile it to the regular variable instead (but still never let reassign the variable in the script)

i'd rather have it defined as a function that always returns the same literal

[Mte90]

The idea of a function that returns always the same value I think that is the best and assure that can't change.

[mks-h]

I'd say go with the @Ph0enixKM idea, since functions have an additional performance penalty. It doesn't matter that a constant is technically a regular variable, so long as it is translated from an Amber constant, thus is proven to be impossible to modify.

[Mte90]

I think that we can move on with a function that return always the same value so we can assure the best compatibility.
In the future we can think for something more sophisticated.

[Ph0enixKM]

In order to resolve this discussion I've created the following poll: #493

[b1ek]

@Ph0enixKM im confused, though. afaik we don't support sh right now. why is it an issue?

[Ph0enixKM]

I think that we eventually will support sh. I just wanted to settle down how are we going to solve this problem holistically (including sh even if we do not implement it's support just yet)

[Ph0enixKM]

This looks pretty good @b1ek. It would be nice to improve that error message. I'll create issues to add constants to our editor plugins

[hdwalters]

Approved subject to suggestions from both myself and @Ph0enixKM.

[Ph0enixKM]

I think that we'll have to write a guideline on writing error messages. But that's not a hurry. Let's merge the feature

[Mte90]

@b1ek can you fix the conflicts so we can merge it?

[lens0021]

x is a variable in the amber side, but $ x $ is a variable in the bash. Should this be $ {nameof x}=123 $ to some forward compatibility?