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Exclude text arrays from the Rubocop for adding limits to texts

Problem description

Adding a limit to a text array using add_text_limit results to an error because it tries to: char_length(text[]) <= #{limit}

At the moment our Cops for enforcing strings and limits on texts both do not take into account that case:

  1. The first one requires the migration to use text[] instead of string[]
  2. The second one complains if the text[] has not an add_text_limit for it

Additional Info

Adding a limit to a array (i.e. how many elements it can include) is a no-op in Postgres: 8.15.1. Declaration of Array Types

[..] However, the current implementation ignores any supplied array size limits, i.e., the behavior is the same as for arrays of unspecified length.

The current implementation does not enforce the declared number of dimensions either. Arrays of a particular element type are all considered to be of the same type, regardless of size or number of dimensions. So, declaring the array size or number of dimensions in CREATE TABLE is simply documentation; it does not affect run-time behavior. [..]

Additionally, adding a character length limit on each element of a text array requires a pretty involved (and expensive) process:

  1. Create a function that unnests the text array and checks each element
  2. Add a check constraint using that function

Solution

I am not sure whether we have a use case where we want to impose a text limit on the individual elements of a text array.

Given the complicated nature of adding the function above, I thing that until such a need arises, we should:

  1. Update the Cops that require texts instead of strings and enforce limits on text columns to not complain when arrays are added

  2. Add a section on the documentation for adding textual data types in migrations with what we should do when we want to add a string/text array

/cc @gitlab-org/database-team

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