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BracesOnWhenStatements.kt
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BracesOnWhenStatements.kt
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package io.gitlab.arturbosch.detekt.rules.style
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 org.jetbrains.kotlin.psi.KtBlockExpression
import org.jetbrains.kotlin.psi.KtWhenEntry
import org.jetbrains.kotlin.psi.KtWhenExpression
import org.jetbrains.kotlin.psi.psiUtil.siblings
/**
* This rule detects `when` statements which do not comply with the specified policy.
* Keeping braces consistent will improve readability and avoid possible errors.
*
* Single-line `when` statement is:
* a `when` where each of the branches are single-line (has no line breaks `\n`).
*
* Multi-line `when` statement is:
* a `when` where at least one of the branches is multi-line (has a break line `\n`).
*
* Available options are:
* * `never`: forces no braces on any branch.
* _Tip_: this is very strict, it will force a simple expression, like a single function call / expression.
* Extracting a function for "complex" logic is one way to adhere to this policy.
* * `necessary`: forces no braces on any branch except where necessary for multi-statement branches.
* * `consistent`: ensures that braces are consistent within `when` statement.
* If there are braces on one of the branches, all branches should have it.
* * `always`: forces braces on all branches.
*
* <noncompliant>
* // singleLine = 'never'
* when (a) {
* 1 -> { f1() }
* 2 -> f2()
* }
* // multiLine = 'never'
* when (a) {
* 1 -> {
* f1()
* }
* 2 -> f2()
* }
* // singleLine = 'necessary'
* when (a) {
* 1 -> { f1() }
* }
* // multiLine = 'necessary'
* when (a) {
* 1 -> {
* f1()
* }
* }
*
* // singleLine = 'consistent'
* when (a) {
* 1 -> { f1() }
* 2 -> f2()
* }
* // multiLine = 'consistent'
* when (a) {
* 1 ->
* f1()
* 2 -> {
* f2()
* f3()
* }
* }
*
* // singleLine = 'always'
* when (a) {
* 1 -> { f1() }
* 2 -> f2()
* }
* // multiLine = 'always'
* when (a) {
* 1 ->
* f1()
* 2 -> {
* f2()
* f3()
* }
* }
*
* </noncompliant>
*
* <compliant>
* // singleLine = 'never'
* when (a) {
* 1 -> f1()
* 2 -> f2()
* }
* // multiLine = 'never'
* when (a) {
* 1 ->
* f1()
* 2 -> f2()
* }
* // singleLine = 'necessary'
* when (a) {
* 1 -> f1()
* 2 -> f2()
* }
* // multiLine = 'necessary'
* when (a) {
* 1 ->
* f1()
* 2 -> {
* f2()
* f3()
* }
* }
*
* // singleLine = 'consistent'
* when (a) {
* 1 -> { f1() }
* 2 -> { f2() }
* }
* when (a) {
* 1 -> f1()
* 2 -> f2()
* }
* // multiLine = 'consistent'
* when (a) {
* 1 -> {
* f1()
* }
* 2 -> {
* f2()
* f3()
* }
* }
*
* // singleLine = 'always'
* when (a) {
* 1 -> { f1() }
* 2 -> { f2() }
* }
* // multiLine = 'always'
* when (a) {
* 1 -> {
* f1()
* }
* 2 -> {
* f2()
* f3()
* }
* }
*
* </compliant>
*/
class BracesOnWhenStatements(config: Config = Config.empty) : Rule(config) {
override val issue = Issue(
javaClass.simpleName,
Severity.Style,
"Braces do not comply with the specified policy",
Debt.FIVE_MINS
)
@Configuration("single-line braces policy")
private val singleLine: BracePolicy by config("necessary") { BracePolicy.getValue(it) }
@Configuration("multi-line braces policy")
private val multiLine: BracePolicy by config("consistent") { BracePolicy.getValue(it) }
override fun visitWhenExpression(expression: KtWhenExpression) {
super.visitWhenExpression(expression)
validate(expression.entries, policy(expression))
}
private fun validate(branches: List<KtWhenEntry>, policy: BracePolicy) {
val violators = when (policy) {
BracePolicy.Always -> {
branches.filter { !it.hasBraces() }
}
BracePolicy.Necessary -> {
branches.filter { !it.isMultiStatement() && it.hasBraces() }
}
BracePolicy.Never -> {
branches.filter { it.hasBraces() }
}
BracePolicy.Consistent -> {
val braces = branches.count { it.hasBraces() }
val noBraces = branches.count { !it.hasBraces() }
if (braces != 0 && noBraces != 0) {
branches.take(1)
} else {
emptyList()
}
}
}
violators.forEach { report(it, policy) }
}
private fun KtWhenEntry.hasBraces(): Boolean = expression is KtBlockExpression
private fun KtWhenEntry.isMultiStatement(): Boolean =
expression.let { (it is KtBlockExpression) && (it.statements.size > 1) }
private fun policy(expression: KtWhenExpression): BracePolicy {
val isMultiLine = expression.entries.any { branch ->
branch.arrow
?.siblings(forward = true, withItself = false)
?.any { it.textContains('\n') }
?: false
}
return if (isMultiLine) multiLine else singleLine
}
private fun report(violator: KtWhenEntry, policy: BracePolicy) {
val parent = violator.parent as KtWhenExpression
val reported = when {
violator in parent.entries && policy == BracePolicy.Consistent -> parent.whenKeyword
violator in parent.entries -> violator.arrow
else -> error("Violating element (${violator.text}) is not part of this 'when' (${parent.text})")
} ?: return
val message = when (policy) {
BracePolicy.Always -> "Missing braces on this branch, add them."
BracePolicy.Consistent -> "Inconsistent braces, make sure all branches either have or don't have braces."
BracePolicy.Necessary -> "Extra braces exist on this branch, remove them."
BracePolicy.Never -> "Extra braces exist on this branch, remove them."
}
report(CodeSmell(issue, Entity.from(reported), message))
}
enum class BracePolicy(val config: String) {
Always("always"),
Consistent("consistent"),
Necessary("necessary"),
Never("never");
companion object {
fun getValue(arg: String): BracePolicy =
values().singleOrNull { it.config == arg }
?: error("Unknown value $arg, allowed values are: ${values().joinToString("|")}")
}
}
}