Option to have diesel_cli infer postgres array types as Array<T> instead of Array<Nullable<T>>

[mikeyhew]

Would you accept a PR that adds this as a configuration option to diesel.toml? We're in the process of upgrading from diesel 1.4 to diesel 2 and have a lot of postgres arrays in our schema, and the change to Array<Nullable> adds extra complexity to avoid an issue that we haven't encountered so far (arrays having null values). Our current workaround is to generate a schema.patch file that replaces all occurences of Array<Nullable> with Array, but it would be more robust if we could configure diesel_cli to infer Array as it did in diesel 1.x.

[weiznich]

Such an option sounds quite specific to me, although I can understand the need for this. I personally would like to go with a more generic approach there, that would introduce a general mechanism for remapping field types. Something like having a set of lookups in your diesel.toml that let you map to arbitrary types:

[[print_schema.type_map]]
database_typename = "int[]" #optional, maybe that can/should be a regex
schema_typename = "Array<Integer>" # optional, drop the column if not set
table_name = "foo" # optional, restrict to a specific table_name
schema_name = "bar" # optional, restrict to a specific schema name
column_name = "baz" # optional, restrict to a specific column name

(Field names, etc are obviously up for discussion)

I believe such a feature would not only address this specific use-case but allow to replace a large number of usages of schema.patch files.

[mikeyhew]

That seems like an interesting idea. For our use case of reverting to Array<T> instead of Array<Nullable<T>> we'd have to add an entry to the map for every array type in our schema, which isn't ideal but could be an improvement over the generated schema patch we're using right now

[weiznich]

I would expect that you should be able to cover that with a single regex for the type name, assuming that we go for the regex supported variant there.

[mikeyhew]

I was thinking the same but noticed this issue. Let's say we have this in our diesel.toml

[[print_schema.type_map]]
database_typename = "([^[\\]]+)[]"
schema_typename = "Array<$1>"

For int[] this would output Array<int>, but what we actually want is Array<Int4>

[weiznich]

Right, that wouldn't work. :(

That said: I don't think it wouldn't that bad to list all array types on it's own.

I'm happy to mentor an implementation of this feature, but I personally do currently not have the capacity to work on this.