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107 lines
3.0 KiB
Elm
107 lines
3.0 KiB
Elm
module NoUselessSubscriptions exposing (rule)
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{-|
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@docs rule
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-}
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import Elm.Syntax.Declaration as Declaration exposing (Declaration)
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import Elm.Syntax.Expression as Expression
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import Elm.Syntax.Node as Node exposing (Node(..))
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import Review.Rule as Rule exposing (Error, Rule)
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{-| Reports `subscriptions` functions that never return a subscription.
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In my opinion, this is often a sign of premature architectural work, where you
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set up an `init`, `view`, `update` and `subscriptions` functions. I think
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it is better to define them as they are needed, to avoid adding upfront complexity
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that turn out to be unnecessary later.
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config =
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[ NoUselessSubscriptions.rule
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]
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## Fail
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subscriptions : Model -> Sub Msg
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subscriptions model =
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Sub.none
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## Success
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main =
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Browser.element
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{ init = init
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, update = update
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, subscriptions = \_ -> Sub.none
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, view = view
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}
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## Try it out
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You can try this rule out by running the following command:
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```bash
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elm-review --template jfmengels/elm-review-the-elm-architecture/example --rules NoUselessSubscriptions
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```
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-}
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rule : Rule
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rule =
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Rule.newModuleRuleSchema "NoUselessSubscriptions" ()
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|> Rule.withSimpleDeclarationVisitor declarationVisitor
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|> Rule.fromModuleRuleSchema
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declarationVisitor : Node Declaration -> List (Error {})
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declarationVisitor declaration =
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case Node.value declaration of
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Declaration.FunctionDeclaration function ->
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if
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(function.declaration
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|> Node.value
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|> .name
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|> Node.value
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)
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== "subscriptions"
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then
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case Node.value function.declaration |> .expression |> Node.value of
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Expression.FunctionOrValue [ "Sub" ] "none" ->
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[ error function
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]
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Expression.Application [ Node _ (Expression.FunctionOrValue [] "always"), Node _ (Expression.FunctionOrValue [ "Sub" ] "none") ] ->
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[ error function
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]
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Expression.Application [ Node _ (Expression.FunctionOrValue [ "Basics" ] "always"), Node _ (Expression.FunctionOrValue [ "Sub" ] "none") ] ->
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[ error function
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]
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Expression.Application [ Node _ (Expression.FunctionOrValue [ "Sub" ] "batch"), Node _ (Expression.ListExpr []) ] ->
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[ error function
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]
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_ ->
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[]
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else
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[]
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_ ->
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[]
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error : Expression.Function -> Error {}
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error function =
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Rule.error
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{ message = "The `subscription` function never returns any subscriptions"
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, details = [ "The `subscription` function never returns any subscriptions. You might as well remove it." ]
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}
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(Node.value function.declaration |> .expression |> Node.range)
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