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113 lines
2.5 KiB
Elm
113 lines
2.5 KiB
Elm
module NoBooleanCaseOf exposing (rule)
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{-|
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@docs rule
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-}
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import Elm.Syntax.Expression as Expression exposing (Expression)
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import Elm.Syntax.Node as Node exposing (Node)
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import Elm.Syntax.Pattern as Pattern exposing (Pattern)
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import Review.Rule as Rule exposing (Error, Rule)
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{-| Reports when pattern matching is used for a boolean value.
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The idiomatic way to check for a condition is to use an `if` expression.
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Read more about it at: <https://guide.elm-lang.org/core_language.html#if-expressions>
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config =
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[ NoBooleanCaseOf.rule
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]
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This won't report pattern matching when a boolean is part of the evaluated value.
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## Fail
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_ =
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case bool of
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True ->
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expression
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False ->
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otherExpression
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## Success
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_ =
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if bool then
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expression
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else
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otherExpression
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_ =
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case ( bool, somethingElse ) of
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( True, SomeThingElse ) ->
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expression
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_ ->
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otherExpression
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# When (not) to use this rule
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You should not use this rule if you do not care about how your boolean values are
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evaluated.
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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-simplification/example --rules NoBooleanCaseOf
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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 "NoBooleanCaseOf" ()
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|> Rule.withSimpleExpressionVisitor expressionVisitor
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|> Rule.fromModuleRuleSchema
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expressionVisitor : Node Expression -> List (Error {})
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expressionVisitor node =
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case Node.value node of
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Expression.CaseExpression { expression, cases } ->
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if List.any (Tuple.first >> isBoolConstructor) cases then
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[ error expression ]
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else
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[]
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_ ->
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[]
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error : Node a -> Error {}
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error node =
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Rule.error
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{ message = "Replace `case..of` by an `if` condition"
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, details =
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[ "The idiomatic way to check for a condition is to use an `if` expression."
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, "Read more about it at: https://guide.elm-lang.org/core_language.html#if-expressions"
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]
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}
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(Node.range node)
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isBoolConstructor : Node Pattern -> Bool
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isBoolConstructor node =
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case Node.value node of
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Pattern.NamedPattern { moduleName, name } _ ->
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(name == "True" || name == "False")
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&& (moduleName == [] || moduleName == [ "Basics" ])
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_ ->
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False
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