Recognize unused variable from type declaration

[straight-shoota]

Lint/UselessAssign rule reports local variables that are defined per assignment but never used.

a = "" # Lint/UselessAssign: Useless assignment to variable `b`

Type declarations also declare a variable yet do not assign to the variable. This should even more reason to report it.

For the following program, ameba should report a similar issue:

a : String

This came up in crystal-lang/crystal#14058

[straight-shoota]

@Sija citing #430 (comment) here for clarity:

As type declarations are often used as part of DSLs and within accessor macros, I see no reliable way to mark them as unused assignments.

I'm not sure I get the issue you're seeing. For all I can tell, the use of type declarations in DSLs and accessor macros should be pretty much the same as with assignments. Ameba is able to handle getter foo = 1, right? Why is getter foo : Int32 problematic?

[Sija]

For all I can tell, the use of type declarations in DSLs and accessor macros should be pretty much the same as with assignments.

Ameba itself allows/uses them within the properties macro.
Perhaps it would be possible to exclude 'em somehow... just thinking out loud here.

Ameba is able to handle getter foo = 1, right? Why is getter foo : Int32 problematic?

Good question. I believe it's due to some custom logic I've missed in the PR.