trailing commas on dictionaries should be all or none

[docwhat]

Introduction

Uneven commas can make terraform code confusing. On dictionaries, they should either be on all or none.

I would expect that tflint would raise an warning on this snippet of code:

locals {
  a_dictionary = {
    "one"  = "fish"
    "two"  = "fish",
    "red"  = "fish"
    "blue" = "fish"
  }
}

I would expect the two line to be flagged as the rest of the lines do not have commas.

Proposal

The rule should take these values:

• all: All dictionary entries should end in a comma.
• none: All dictionary entries should not end in a comma.
• match: All the dictionary entries in a given dictionary should be the same; either all commas or all without commas.

References

None

[bendrucker]

At this time the terraform ruleset covers official recommendations from the Terraform docs. Outside of these official recommendations, we are not accepting style enforcement rules into any official rulesets in this org. See terraform-linters/tflint-ruleset-terraform#22 for discussion.

You're of course free to implement your own ruleset plugin. If you publish one, it would be great if you'd share the URL here in case others are looking for a similar rule.