Remove unused type `Copilot.Core.Expr.Tag`

[ivanperez-keera]

Description

The type Copilot.Core.Expr.Tag was deprecated in Copilot 3.6 because it was not used and therefore did not belong in the program.

As per our internal policy of waiting 3 versions from deprecation until a public interface declaration can be removed, this type can now be removed completely.

Type

• Bug: unused code included in the implementation; a type declared does not have a complete API.

Additional context

• Issue: The type copilot-core:Copilot.Core.Expr.Tag is not used #260.

Requester

• Ivan Perez

Method to check presence of bug

The following expression finds uses of Tag, ignoring appearances in comments or strings.

$ grep -nHre '\<Tag\>' --include='*.hs' | grep -ve '^{-#' | grep -ve '--.*Tag' | grep -ve '"[^"]*Tag[^"]*"'
copilot-core/src/Copilot/Core/Expr.hs:15:  , Tag
copilot-core/src/Copilot/Core/Expr.hs:43:type Tag = Int

The result obtained are two lines: the definition, and it being exported. Tags are not required by Copilot's requirements, and therefore should not be published.

Expected result

The string should be either empty (no type exists) or list further uses.

Desired result

The string returned by the command above should be empty.

Proposed solution

Removing the type declaration from the module Copilot.Core.Expr, as well as its export from the module's export list.

Further notes

See 0f536ec for a confirmation of when the type was deprecated.

[ivanperez-keera]

Change Manager: Confirmed that the bug is present by using method described and examining the result.

[ivanperez-keera]

Technical Lead: Confirmed that the bug should be addressed.

[ivanperez-keera]

Technical Lead: Bug scheduled for fixing in Copilot 3.9.

Fix assigned to: @ivanperez-keera .