fix: Fixed SG with prefix lists

[ghost]

Custom rules with prefix lists were failing in cases where no CIDR block was specified due to an edge case in the variable interpolation.

If both the rule and the general CIDR block variables are unset, the interpolation returns a list with an empty string as the only element (instead of an empty list).

main.tf has been modified to add a check for this edge case and return an empty list.

Description

The eight (8) resources in main.tf which set the cidr_blocks or ipv6_cidr_blocks argument have been modified to include a check for the edge case where both the custom rule does not include a CIDR block and the corresponding global CIDR block variable is unset (defaulting to an empty list). These resources now correctly evaluate their respective CIDR block arguments to an empty list, allowing the rules to be created with the assigned prefix list id(s).

All eight (8) changes follow the pattern below (in pseudo-code):

IF (rule cidr block is set) OR (global cidr block is set)
THEN (do previous behavior) 
ELSE (return empty list)
END

This preserves the original behavior in all cases except for the edge case, which now returns an empty list.

Motivation and Context

As of v4.16.2, the module does not allow for custom rules to be specified without a CIDR block, even if provided one or more prefix list ids. This appears to be due to a variable interpolation edge case, which is incorrectly returning a list with an empty string (i.e. [""]) instead of an empty list (i.e. []). A check has been added to override the interpolation and return an empty list for this edge case, which allows the security group and SG rule(s) to be created as expected.

Link to issue: #270

Fixes #270

Breaking Changes

All changes are backwards-compatible; I believe this can be safely released as a bug fix.

How Has This Been Tested?

This change has been tested against my code base.

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

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[apamildner]

@antonbabenko Can we have this one merged/reviewed please?

[apamildner]

LGTM!

[loicvolle]

LGTM

[antonbabenko]

This PR is included in version 4.17.1 🎉

[github-actions]

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