[BUG] [Elm] Outputs duplicate types, as well as overlapping types with same name

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?

• Using the full Stripe API spec.

• Have you validated the input using an OpenAPI validator (example)?

• I used the CLI with validate and it found no issues.

• Have you tested with the latest master to confirm the issue still exists?

• Yes

• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

openapi-generator version

Latest master

OpenAPI declaration file content or url

https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json

Generation Details

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate    -i https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json    -g elm    -o ./elm-stripeFix

All in the same file, there will be this Status:

type Status
    = StatusActive
    | StatusBlocked
    | StatusInactive


statusVariants : List Status
statusVariants =
    [ StatusActive
    , StatusBlocked
    , StatusInactive
    ]


stringFromStatus : Status -> String
stringFromStatus model =
    case model of
        StatusActive ->
            "active"

        StatusBlocked ->
            "blocked"

        StatusInactive ->
            "inactive"

...right along with this Status somewhere else:

type Status
    = StatusExpired
    | StatusLost
    | StatusSubmitted
    | StatusUnsubmitted
    | StatusWon


statusVariants : List Status
statusVariants =
    [ StatusExpired
    , StatusLost
    , StatusSubmitted
    , StatusUnsubmitted
    , StatusWon
    ]


stringFromStatus : Status -> String
stringFromStatus model =
    case model of
        StatusExpired ->
            "expired"

        StatusLost ->
            "lost"

        StatusSubmitted ->
            "submitted"

        StatusUnsubmitted ->
            "unsubmitted"

        StatusWon ->
            "won"

Obviously this causes a conflict, and fixing it is not trivial as all references to Status are now ambiguous.

Suggest a fix

Ideally, have types belonging to different domains go in separate type modules.

At the least, add a number or underscore to the end of one of them if need be.

Naive fix would be to merge the enums and just treat them as one.

Also, this includes totally identical types and encoder/decoders. They can have everything exactly the same, and still be repeated 5 different places in the file.

Reproduce the issue with the Stripe OpenAPI specification and the Elm generation command shown in the report, then inspect the generated Elm output for duplicate and colliding types. Done means generated types and their encoders, decoders, and references no longer conflict, while identical definitions are not repeated.