RedundantElseInWhenSpec.kt

package io.gitlab.arturbosch.detekt.rules.bugs

import io.gitlab.arturbosch.detekt.rules.KotlinCoreEnvironmentTest
import io.gitlab.arturbosch.detekt.test.compileAndLintWithContext
import io.gitlab.arturbosch.detekt.test.lintWithContext
import org.assertj.core.api.Assertions.assertThat
import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
import org.junit.jupiter.api.Nested
import org.junit.jupiter.api.Test

@KotlinCoreEnvironmentTest
class RedundantElseInWhenSpec(private val env: KotlinCoreEnvironment) {
    private val subject = RedundantElseInWhen()

    @Nested
    inner class `enum` {
        @Test
        fun `reports when _when_ expression used as statement contains _else_ case when all cases already covered`() {
            val code = """
            enum class Color {
                RED,
                GREEN,
                BLUE
            }

            fun whenOnEnumFail(c: Color) {
                when (c) {
                    Color.BLUE -> {}
                    Color.GREEN -> {}
                    Color.RED -> {}
                    else -> {}
                }
            }
            """
            val actual = subject.compileAndLintWithContext(env, code)
            assertThat(actual).hasSize(1)
        }

        @Test
        fun `reports when _when_ expression contains _else_ case when all cases already covered`() {
            val code = """
            enum class Color {
                RED,
                GREEN,
                BLUE
            }

            fun whenOnEnumFail(c: Color) {
                val x = when (c) {
                    Color.BLUE -> 1
                    Color.GREEN -> 2
                    Color.RED -> 3
                    else -> 100
                }
            }
            """
            val actual = subject.compileAndLintWithContext(env, code)
            assertThat(actual).hasSize(1)
        }

        @Test
        fun `does not report when _when_ expression contains _else_ case when not all cases explicitly covered`() {
            val code = """
            enum class Color {
                RED,
                GREEN,
                BLUE
            }

            fun whenOnEnumPass(c: Color) {
                when (c) {
                    Color.BLUE -> {}
                    Color.GREEN -> {}
                    else -> {}
                }

                val x = when (c) {
                    Color.BLUE -> 1
                    Color.GREEN -> 2
                    else -> 100
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when _when_ expression does not contain else case`() {
            val code = """
            enum class Color {
                RED,
                GREEN,
                BLUE
            }

            fun whenOnEnumPassA(c: Color) {
                when (c) {
                    Color.BLUE -> {}
                    Color.GREEN -> {}
                    Color.RED -> {}
                }

                val x = when (c) {
                    Color.BLUE -> 1
                    Color.GREEN -> 2
                    Color.RED -> 3
                }
            }

            fun whenOnEnumPassB(c: Color) {
                when (c) {
                    Color.BLUE -> {}
                    Color.GREEN -> {}
                }
            }
            """
            assertThat(subject.lintWithContext(env, code)).isEmpty()
        }
    }

    @Nested
    inner class `sealed classes` {
        @Test
        fun `reports when _when_ expression used as statement contains _else_ case when all cases already covered`() {
            val code = """
                sealed class Variant {
                    object VariantA : Variant()
                    class VariantB : Variant()
                    object VariantC : Variant()
                }

                fun whenOnEnumFail(v: Variant) {
                    when (v) {
                        is Variant.VariantA -> {}
                        is Variant.VariantB -> {}
                        is Variant.VariantC -> {}
                        else -> {}
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `reports when _when_ expression contains _else_ case when all cases already covered`() {
            val code = """
                sealed class Variant {
                    object VariantA : Variant()
                    class VariantB : Variant()
                    object VariantC : Variant()
                }

                fun whenOnEnumFail(v: Variant) {
                    val x = when (v) {
                        is Variant.VariantA -> "a"
                        is Variant.VariantB -> "b"
                        is Variant.VariantC -> "c"
                        else -> "other"
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `does not report when _when_ expression contains _else_ case when not all cases explicitly covered`() {
            val code = """
                sealed class Variant {
                    object VariantA : Variant()
                    class VariantB : Variant()
                    object VariantC : Variant()
                }

                fun whenOnEnumPass(v: Variant) {
                    when (v) {
                        is Variant.VariantA -> {}
                        is Variant.VariantB -> {}
                        else -> {}
                    }

                    val x = when (v) {
                        is Variant.VariantA -> "a"
                        is Variant.VariantB -> "b"
                        else -> "other"
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when _when_ expression does not contain else case`() {
            val code = """
                sealed class Variant {
                    object VariantA : Variant()
                    class VariantB : Variant()
                    object VariantC : Variant()
                }

                fun whenOnEnumPass(v: Variant) {
                    when (v) {
                        is Variant.VariantA -> {}
                        is Variant.VariantB -> {}
                    }
                }
            """
            assertThat(subject.lintWithContext(env, code)).isEmpty()
        }
    }

    @Nested
    inner class `standard when` {
        @Test
        fun `does not report when _when_ not checking for missing cases`() {
            val code = """
                fun whenChecks() {
                    val x = 3
                    val s = "3"

                    when (x) {
                        0, 1 -> print("x == 0 or x == 1")
                        else -> print("otherwise")
                    }

                    when (x) {
                        Integer.parseInt(s) -> print("s encodes x")
                        else -> print("s does not encode x")
                    }

                    when (x) {
                        in 1..10 -> print("x is in the range")
                        !in 10..20 -> print("x is outside the range")
                        else -> print("none of the above")
                    }

                    val y = when(s) {
                        is String -> s.startsWith("prefix")
                        else -> false
                    }

                    when {
                        x.equals(s) -> print("x equals s")
                        x.plus(3) == 4 -> print("x is 1")
                        else -> print("x is funny")
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }
    }
}