Report `[for k, v in set: k]` as anti-pattern diagnostic

[radeksimko]

Language Server Version

v0.32.6

Problem Statement

Users can today use the following syntax to loop over a set:

variable "set" {
  type    = set(string)
  default = ["aaa", "bbb"]
}

output "test" {
  value = [for key, val in var.set : key]
}

This is functionally equivalent to

variable "set" {
  type    = set(string)
  default = ["aaa", "bbb"]
}

output "test" {
  value = [for key, val in var.set : val]
}

In other words, looping over "set keys" is allowed but sets are not sorted (hence don't have indexes like lists or tuples) and don't really have their own keys either (like maps or objects).

Therefore, out of the two examples, only the bottom one should be considered best practice.

Attempted Solutions

No response

Proposal

• Report looping over set keys as warning diagnostic
• Provide quick fix code action to replace key with value reference

Related LSP methods

No response

References

No response

Help Wanted

• I'm interested in contributing a fix myself

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