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Potential new rule: DoubleNegativeLambda #5937
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Original file line number | Diff line number | Diff line change | ||||||||||||||||||||||
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package io.gitlab.arturbosch.detekt.rules.style | ||||||||||||||||||||||||
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import io.gitlab.arturbosch.detekt.api.CodeSmell | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Config | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Debt | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Entity | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Issue | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Rule | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.Severity | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.config | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.internal.Configuration | ||||||||||||||||||||||||
import io.gitlab.arturbosch.detekt.api.valuesWithReason | ||||||||||||||||||||||||
import org.jetbrains.kotlin.lexer.KtTokens | ||||||||||||||||||||||||
import org.jetbrains.kotlin.psi.KtCallExpression | ||||||||||||||||||||||||
import org.jetbrains.kotlin.psi.KtExpression | ||||||||||||||||||||||||
import org.jetbrains.kotlin.psi.KtOperationReferenceExpression | ||||||||||||||||||||||||
import org.jetbrains.kotlin.psi.psiUtil.collectDescendantsOfType | ||||||||||||||||||||||||
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/** | ||||||||||||||||||||||||
* Detects negation in lambda blocks where the function name is also in the negative (like `takeUnless`). | ||||||||||||||||||||||||
* A double negative is harder to read than a positive. In particular, if there are multiple conditions with `&&` etc. inside | ||||||||||||||||||||||||
* the lambda, then the reader may need to unpack these using DeMorgan's laws. Consider rewriting the lambda to use a positive version | ||||||||||||||||||||||||
* of the function (like `takeIf`). | ||||||||||||||||||||||||
* | ||||||||||||||||||||||||
* <noncompliant> | ||||||||||||||||||||||||
* fun Int.evenOrNull() = takeUnless { it % 2 != 0 } | ||||||||||||||||||||||||
* </noncompliant> | ||||||||||||||||||||||||
* <compliant> | ||||||||||||||||||||||||
* fun Int.evenOrNull() = takeIf { it % 2 == 0 } | ||||||||||||||||||||||||
* </compliant> | ||||||||||||||||||||||||
*/ | ||||||||||||||||||||||||
class DoubleNegativeLambda(config: Config = Config.empty) : Rule(config) { | ||||||||||||||||||||||||
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override val issue = Issue( | ||||||||||||||||||||||||
"DoubleNegativeLambda", | ||||||||||||||||||||||||
Severity.Style, | ||||||||||||||||||||||||
"Double negative from a function name expressed in the negative (like `takeUnless`) with a lambda block " + | ||||||||||||||||||||||||
"that also contains negation. This is more readable when rewritten using a positive form of the function " + | ||||||||||||||||||||||||
"(like `takeIf`).", | ||||||||||||||||||||||||
Debt.FIVE_MINS, | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
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private val splitCamelCaseRegex = "(?<=[a-z])(?=[A-Z])".toRegex() | ||||||||||||||||||||||||
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private val negationTokens = listOf( | ||||||||||||||||||||||||
KtTokens.EXCL, | ||||||||||||||||||||||||
KtTokens.EXCLEQ, | ||||||||||||||||||||||||
KtTokens.EXCLEQEQEQ, | ||||||||||||||||||||||||
KtTokens.NOT_IN, | ||||||||||||||||||||||||
KtTokens.NOT_IS, | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
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@Configuration( | ||||||||||||||||||||||||
"Function names expressed in the negative that can form double negatives with their lambda blocks. " + | ||||||||||||||||||||||||
"These are grouped together with the positive counterpart of the function, or `null` if this is unknown." | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
private val negativeFunctions: List<NegativeFunction> by config( | ||||||||||||||||||||||||
valuesWithReason( | ||||||||||||||||||||||||
"takeUnless" to "takeIf", | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
) { list -> | ||||||||||||||||||||||||
list.map { NegativeFunction(simpleName = it.value, positiveCounterpart = it.reason) } | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
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@Configuration( | ||||||||||||||||||||||||
"Function name parts to look for in the lambda block when deciding " + | ||||||||||||||||||||||||
"if the lambda contains a negative." | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
private val negativeFunctionNameParts: Set<String> by config(listOf("not", "non")) { it.toSet() } | ||||||||||||||||||||||||
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override fun visitCallExpression(expression: KtCallExpression) { | ||||||||||||||||||||||||
super.visitCallExpression(expression) | ||||||||||||||||||||||||
val calleeExpression = expression.calleeExpression?.text ?: return | ||||||||||||||||||||||||
val negativeFunction = negativeFunctions.firstOrNull { it.simpleName == calleeExpression } ?: return | ||||||||||||||||||||||||
val lambdaArgument = expression.lambdaArguments.firstOrNull() ?: return | ||||||||||||||||||||||||
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val forbiddenChildren = lambdaArgument.collectDescendantsOfType<KtExpression> { | ||||||||||||||||||||||||
it.isForbiddenNegation() | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
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if (forbiddenChildren.isNotEmpty()) { | ||||||||||||||||||||||||
report( | ||||||||||||||||||||||||
CodeSmell( | ||||||||||||||||||||||||
issue, | ||||||||||||||||||||||||
Entity.from(expression), | ||||||||||||||||||||||||
formatMessage(forbiddenChildren, negativeFunction) | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
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private fun KtExpression.isForbiddenNegation(): Boolean { | ||||||||||||||||||||||||
return when (this) { | ||||||||||||||||||||||||
is KtOperationReferenceExpression -> operationSignTokenType in negationTokens | ||||||||||||||||||||||||
is KtCallExpression -> text == "not()" || text.split(splitCamelCaseRegex).map { it.lowercase() } | ||||||||||||||||||||||||
.any { it in negativeFunctionNameParts } | ||||||||||||||||||||||||
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else -> false | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
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private fun formatMessage( | ||||||||||||||||||||||||
forbiddenChildren: List<KtExpression>, | ||||||||||||||||||||||||
negativeFunction: NegativeFunction, | ||||||||||||||||||||||||
) = buildString { | ||||||||||||||||||||||||
append("Double negative through using ${forbiddenChildren.joinInBackTicks()} inside a ") | ||||||||||||||||||||||||
append("`${negativeFunction.simpleName}` lambda. ") | ||||||||||||||||||||||||
append("Rewrite in the positive") | ||||||||||||||||||||||||
if (negativeFunction.positiveCounterpart != null) { | ||||||||||||||||||||||||
append(" with `${negativeFunction.positiveCounterpart}`.") | ||||||||||||||||||||||||
} else { | ||||||||||||||||||||||||
append(".") | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more.
Suggested change
I think that There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Thanks, that makes a lot more sense. I did the change in 2ded6a4 I called it a "recommendation" ("Use but I can rename it back to "reason" if you prefer. |
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} | ||||||||||||||||||||||||
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private fun List<KtExpression>.joinInBackTicks() = joinToString { "`${it.text}`" } | ||||||||||||||||||||||||
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/** | ||||||||||||||||||||||||
* A function that can form a double negative with its lambda. | ||||||||||||||||||||||||
*/ | ||||||||||||||||||||||||
private data class NegativeFunction( | ||||||||||||||||||||||||
val simpleName: String, | ||||||||||||||||||||||||
val positiveCounterpart: String?, | ||||||||||||||||||||||||
) | ||||||||||||||||||||||||
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companion object { | ||||||||||||||||||||||||
const val NEGATIVE_FUNCTIONS = "negativeFunctions" | ||||||||||||||||||||||||
const val NEGATIVE_FUNCTION_NAME_PARTS = "negativeFunctionNameParts" | ||||||||||||||||||||||||
} | ||||||||||||||||||||||||
} |
Original file line number | Diff line number | Diff line change |
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package io.gitlab.arturbosch.detekt.rules.style | ||
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import io.gitlab.arturbosch.detekt.api.Config | ||
import io.gitlab.arturbosch.detekt.api.ValueWithReason | ||
import io.gitlab.arturbosch.detekt.test.TestConfig | ||
import io.gitlab.arturbosch.detekt.test.assertThat | ||
import io.gitlab.arturbosch.detekt.test.compileAndLint | ||
import io.gitlab.arturbosch.detekt.test.toConfig | ||
import org.junit.jupiter.api.Test | ||
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class DoubleNegativeLambdaSpec { | ||
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private val subject = DoubleNegativeLambda(Config.empty) | ||
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@Test | ||
fun `reports simple logical not`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isEven() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { !it.isEven() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports logical not in binary expression`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isEven() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { it > 0 && !it.isEven() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports logical not prefixing brackets`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isEven() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { !(it == 0 || it.isEven()) } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports negation inside nested lambda`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isEven() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { it.isEven().takeIf { i -> !i } ?: false } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports double nested negation`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isEven() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { it.isEven().takeUnless { i -> !i } ?: false } | ||
""".trimIndent() | ||
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val findings = subject.compileAndLint(code) | ||
assertThat(findings).hasSize(2) | ||
assertThat(findings[0]).hasSourceLocation(3, 62) // second takeUnless | ||
assertThat(findings[1]).hasSourceLocation(3, 37) // first takeUnless | ||
} | ||
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@Test | ||
fun `reports function with 'not' in the name`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isNotZero() = this != 0 | ||
val rand = Random.Default.nextInt().takeUnless { it.isNotZero() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports zero-param function with 'non' in the name`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isNonNegative() = 0 < this | ||
val rand = Random.Default.nextInt().takeUnless { it.isNonNegative() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports single-param function with 'non' in the name`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isNotGreaterThan(other: Int) = other < this | ||
val rand = Random.Default.nextInt().takeUnless { it.isNotGreaterThan(0) } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports not equal`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
val rand = Random.Default.nextInt().takeUnless { it != 0 } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports not equal by reference`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
val rand = Random.Default.nextInt().takeUnless { it !== 0 } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports !in`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
val rand = Random.Default.nextInt().takeUnless { it !in 1..3 } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports !is`() { | ||
val code = """ | ||
val list = listOf(3, "a", true) | ||
val maybeBoolean = list.firstOrNull().takeUnless { it !is Boolean } | ||
""".trimIndent() | ||
assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports use of operator fun not`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
val rand = Random.Default.nextInt().takeUnless { (it > 0).not() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `does not report function with 'not' in part of the name`() { | ||
val code = """ | ||
fun String.hasAnnotations() = this.contains("annotations") | ||
val nonAnnotated = "".takeUnless { it.hasAnnotations() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).isEmpty() | ||
} | ||
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@Test | ||
fun `does not report non-null assert in takeUnless`() { | ||
val code = """ | ||
val x = "".takeUnless { it!!.isEmpty() } | ||
""".trimIndent() | ||
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assertThat(subject.compileAndLint(code)).isEmpty() | ||
} | ||
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@Test | ||
fun `reports negative function name from config`() { | ||
val config = | ||
TestConfig( | ||
DoubleNegativeLambda.NEGATIVE_FUNCTIONS to listOf( | ||
ValueWithReason(value = "none", reason = "any").toConfig(), | ||
ValueWithReason(value = "filterNot", reason = "filter").toConfig(), | ||
) | ||
) | ||
val code = """ | ||
fun Int.isEven() = this % 2 == 0 | ||
val isValid = listOf(1, 2, 3).filterNot { !it.isEven() }.none { it != 0 } | ||
""".trimIndent() | ||
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assertThat(DoubleNegativeLambda(config).compileAndLint(code)).hasSize(2) | ||
} | ||
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@Test | ||
fun `reports negative function name parts from config`() { | ||
val config = TestConfig(DoubleNegativeLambda.NEGATIVE_FUNCTION_NAME_PARTS to listOf("isnt")) | ||
val code = """ | ||
import kotlin.random.Random | ||
fun Int.isntOdd() = this % 2 == 0 | ||
val rand = Random.Default.nextInt().takeUnless { it.isntOdd() } | ||
""".trimIndent() | ||
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assertThat(DoubleNegativeLambda(config).compileAndLint(code)).hasSize(1) | ||
} | ||
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@Test | ||
fun `reports multiple negations in message`() { | ||
val code = """ | ||
import kotlin.random.Random | ||
val list: List<Int> = listOf(1, 2, 3) | ||
val rand = Random.Default.nextInt().takeUnless { it !in list && it != 0 } | ||
""".trimIndent() | ||
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val findings = subject.compileAndLint(code) | ||
assertThat(findings).hasSize(1) | ||
assertThat(findings).hasStartSourceLocation(3, 37) | ||
assertThat(findings).hasEndSourceLocation(3, 74) | ||
assertThat(findings[0]).hasMessage( | ||
"Double negative through using `!in`, `!=` inside a `takeUnless` lambda. Rewrite in the positive with `takeIf`." | ||
) | ||
} | ||
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@Test | ||
fun `report for negative function with no positive counterpart`() { | ||
val config = | ||
TestConfig( | ||
DoubleNegativeLambda.NEGATIVE_FUNCTIONS to listOf( | ||
ValueWithReason(value = "none", reason = null).toConfig(), | ||
) | ||
) | ||
val code = """ | ||
val list = listOf(1, 2, 3) | ||
val result = list.none { it != 0 } | ||
""".trimIndent() | ||
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val findings = DoubleNegativeLambda(config).compileAndLint(code) | ||
assertThat(findings[0]).hasMessage( | ||
"Double negative through using `!=` inside a `none` lambda. Rewrite in the positive." | ||
) | ||
} | ||
} |
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