CanBeNonNullableSpec.kt

package io.gitlab.arturbosch.detekt.rules.style

import io.gitlab.arturbosch.detekt.api.Config
import io.gitlab.arturbosch.detekt.rules.KotlinCoreEnvironmentTest
import io.gitlab.arturbosch.detekt.test.compileAndLint
import io.gitlab.arturbosch.detekt.test.compileAndLintWithContext
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 CanBeNonNullableSpec(val env: KotlinCoreEnvironment) {
    val subject = CanBeNonNullable(Config.empty)

    @Test
    fun `does not report when there is no context`() {
        val code = """
            class A {
                private var a: Int? = 5
                fun foo() {
                    a = 6
                }
            }
        """
        assertThat(subject.compileAndLint(code)).isEmpty()
    }

    @Nested
    inner class `evaluating private properties` {
        @Test
        fun `reports when class-level vars are never assigned nullable values`() {
            val code = """
            class A(bVal: Int) {
                private var a: Int? = 5
                private var b: Int?
                
                init {
                    b = bVal
                }
                
                fun foo(): Int {
                    val b = a!!
                    a = b + 1
                    val a = null
                    return b
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
        }

        @Test
        fun `reports when vars utilize non-nullable delegate values`() {
            val code = """
                import kotlin.reflect.KProperty
                
                class A {
                    private var a: Int? by PropDelegate()
                
                    fun foo(): Int {
                        val b = a!!
                        a = b + 1
                        val a = null
                        return b
                    }
                }
                
                class PropDelegate(private var propVal: Int = 0) {
                    operator fun getValue(thisRef: A, property: KProperty<*>): Int {
                        return propVal
                    }
                
                    operator fun setValue(thisRef: A, property: KProperty<*>, value: Any?) {
                        if (value is Int) {
                            propVal = value
                        }
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
        }

        @Test
        fun `reports when file-level vars are never assigned nullable values`() {
            val code = """
            private var fileA: Int? = 5
            private var fileB: Int? = 5

            fun fileFoo() {
                fileB = 6
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
        }

        @Test
        fun `does not report when class-level vars are assigned nullable values`() {
            val code = """
            import kotlin.random.Random

            class A(fVal: Int?) {
                private var a: Int? = 0
                private var b: Int? = 0
                private var c: Int? = 0
                private var d: Int? = 0
                private var e: Int? = null
                private var f: Int?
                
                init {
                    f = fVal
                }

                fun foo(fizz: Int): Int {
                    a = null
                    b = if (fizz % 2 == 0) fizz else null
                    c = buzz(fizz)
                    d = a
                    return fizz
                }

                private fun buzz(bizz: Int): Int? {
                    return if (bizz % 2 == 0) null else bizz
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report vars that utilize nullable delegate values`() {
            val code = """
                class A(private var aDelegate: Int?) {
                    private var a: Int? by this::aDelegate
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when file-level vars are assigned nullable values`() {
            val code = """
            import kotlin.random.Random

            private var fileA: Int? = 5
            private var fileB: Int? = null
            private var fileC: Int? = 5

            fun fileFoo() {
                fileC = null
            }

            class A {
                fun foo() {
                    fileA = null
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `reports when vars with private setters are never assigned nullable values`() {
            val code = """
            class A {
                var a: Int? = 5
                    private set
                fun foo() {
                    a = 6
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `does not report when vars with private setters are assigned nullable values`() {
            val code = """
            class A {
                var a: Int? = 5
                    private set
                fun foo() {
                    a = null
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when vars use public setters`() {
            val code = """
            class A {
                var a: Int? = 5
                fun foo() {
                    a = 6
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when vars use non-private setters`() {
            val code = """
                class A {
                    var a: Int? = 5
                        internal set
                    fun foo() {
                        a = 6
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when private vars are declared in the constructor`() {
            val code = """
            class A(private var a: Int?) {
                fun foo() {
                    a = 6
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }
    }

    @Nested
    inner class `evaluating public properties` {
        @Test
        fun `reports when class-level vals are set to non-nullable values`() {
            val code = """
            class A(cVal: Int) {
                val a: Int? = 5
                val b: Int?
                val c: Int?
                
                init {
                    b = 5
                    c = cVal
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(3)
        }

        @Test
        fun `reports when vals utilize non-nullable delegate values`() {
            val code = """
            class A {
                val a: Int? by lazy {
                    5
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `reports when file-level vals are set to non-nullable values`() {
            val code = """
            val fileA: Int? = 5
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `does not report when class-level vals are assigned a nullable value`() {
            val code = """
            import kotlin.random.Random

            class A(cVal: Int?) {
                val a: Int? = null
                val b: Int?
                val c: Int?
                
                init {
                    b = null
                    c = cVal
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when vals utilize nullable delegate values`() {
            val code = """
            import kotlin.random.Random

            class A {
                val d: Int? by lazy {
                    val randVal = Random.nextInt()
                    if (randVal % 2 == 0) randVal else null
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when file-level vals are assigned a nullable value`() {
            val code = """
            val fileA: Int? = null
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when vals are declared non-nullable`() {
            val code = """
            class A {
                val a: Int = 5
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report when vals are declared in the constructor`() {
            val code = """
            class A(private val a: Int?)
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `reports when vals with getters never return nullable values`() {
            val code = """
            class A {
                val a: Int?
                    get() = 5
                val b: Int?
                    get() {
                        return 5
                    }
                val c: Int?
                    get() = foo()
                
                private fun foo(): Int {
                    return 5
                }
            }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(3)
        }

        @Test
        fun `does not report when vals with getters return potentially-nullable values`() {
            val code = """
                import kotlin.random.Random
                
                class A {
                    val a: Int?
                        get() = Random.nextInt()?.let { if (it % 2 == 0) it else null }
                    val b: Int?
                        get() {
                            return Random.nextInt()?.let { if (it % 2 == 0) it else null }
                        }
                    val c: Int?
                        get() = foo()
                    
                    private fun foo(): Int? {
                        val randInt = Random.nextInt()
                        return if (randInt % 2 == 0) randInt else null
                    }
                }
            """
            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report on non-null properties of a parameterized type`() {
            val code = """
                class P<T>(foo: T) {
                    val a: T = foo
                    val b: T? = null
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `reports on properties of an unnecessarily nullable parameterized type`() {
            val code = """
                class P<T>(foo: T) {
                    val bar: T? = foo
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `reports on properties of an unnecessarily nullable parameterized type extending Any`() {
            val code = """
                class P<T : Any>(foo: T) {
                    val bar: T? = foo
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }

        @Test
        fun `does not report on properties of a parameterized type which must be nullable`() {
            val code = """
                class P<T : Any>(private val foo: T) {
                    val a: T
                        get() = foo
                    val b: T? = foo.takeIf { Random.nextBoolean() }
                    val c: T?
                        get() = foo.takeIf { Random.nextBoolean() }
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `does not report on properties of a parameterized type which resolve to Nothing`() {
            val code = """
                class P<T> {
                    val foo: T
                        get() = error("")
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
        }

        @Test
        fun `reports on properties of an unnecessarily nullable parameterized type which resolve to Nothing`() {
            val code = """
                class P<T> {
                    val foo: T?
                        get() = error("")
                }
            """.trimIndent()

            assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
        }
    }

    @Test
    fun `does not report open properties`() {
        val code = """
            open class A {
                open val a: Int? = 5
                open var b: Int? = 5
            }
        """
        assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
    }

    @Test
    fun `does not report abstract properties`() {
        val code = """
            abstract class A {
                abstract val a: Int?
                abstract var b: Int?
            }
        """
        assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
    }

    @Test
    fun `does not report properties whose initial assignment derives from unsafe non-Java code`() {
        val code = """
            class A(msg: String?) {
                private val e = Exception(msg)
                // e.localizedMessage is marked as String! by Kotlin, meaning Kotlin
                // cannot guarantee that it will be non-null, even though it is treated
                // as non-null in Kotlin code.
                private var a: String? = e.localizedMessage
            }
        """
        assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
    }

    @Test
    fun `does not report interface properties`() {
        val code = """
            interface A {
                val a: Int?
                var b: Int?
            }
        """
        assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
    }

    @Nested
    inner class `nullable function parameters` {
        @Nested
        inner class `using a de-nullifier` {
            @Test
            fun `does report when a param is de-nullified with a postfix expression`() {
                val code = """
                    fun foo(a: Int?) {
                        val b = a!! + 2
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
            }

            @Test
            fun `does report when a param is de-nullified with a dot-qualified expression`() {
                val code = """
                    fun foo(a: Int?) {
                        val b = a!!.plus(2)
                    }

                    fun fizz(b: Int?) = b!!.plus(2)
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
            }

            @Test
            fun `does report when a de-nullifier precondition is called on the param`() {
                val code = """
                    fun foo(a: Int?, b: Int?) {
                        val aNonNull = requireNotNull(a)
                        val c = aNonNull + checkNotNull(b)
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
            }

            @Test
            fun `does not report a double-bang call the field of a non-null param`() {
                val code = """
                    class A(val a: Int?)

                    fun foo(a: A) {
                        val b = a.a!! + 2
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }

            @Test
            fun `does not report on overridden function parameter`() {
                val code = """
                    interface A {
                        fun foo(a: Int?)
                    }
                    
                    class B : A {
                        override fun foo(a: Int?) {
                            val b = a!! + 2 
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }
        }

        @Nested
        inner class `using a null-safe expression` {
            @Nested
            inner class `in initializer` {
                @Test
                fun `does not report when the safe-qualified expression is the only expression of the function`() {
                    val code = """
                        class A {
                            val foo = "BAR"
                        }
                        
                        fun foo(a: A?) = a?.foo
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }
            }

            @Nested
            inner class `in a non-return statement` {
                @Test
                fun `does report when the safe-qualified expression is the only expression of the function`() {
                    val code = """   
                        class A(val foo: String)

                        fun foo(a: A?) {
                            a?.let { println(it.foo) }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does not report when the safe-qualified expression is within a lambda`() {
                    val code = """
                        class A {
                            fun doFoo(callback: () -> Unit) {
                                callback.invoke()
                            }
                        }

                        fun foo(a: String?, aObj: A) {
                            aObj.doFoo {
                                a?.let { println("a not null") }
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does not report when the safe-qualified expression is not the only expression of the function`() {
                    val code = """
                        class A {
                            fun doFoo() { println("FOO") }
                        }
                        
                        fun foo(a: A?) {
                            a?.doFoo()
                            val b = 5 + 2
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }
            }

            @Nested
            inner class `in a return statement` {
                @Test
                fun `does not report when the safe-qualified expression is the only expression of the function`() {
                    val code = """
                        class A {
                            val foo = "BAR"
                        }
                        
                        fun fizz(aObj: A?): String? {
                            return aObj?.foo
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }
            }
        }

        @Nested
        inner class `when statements` {
            @Nested
            inner class `without a subject` {
                @Test
                fun `does not report when the parameter is checked on nullity`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a == null -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does not report when the parameter is checked on nullity in a reversed manner`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                null == a -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does not report when the parameter is checked on nullity with multiple clauses`() {
                    val code = """
                        fun foo(a: Int?, other: Int) {
                            when {
                                a == null && other % 2 == 0 -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does report when the parameter is only checked on non-nullity`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a != null -> println(2 + a)
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does report when the parameter is only checked on non-nullity with multiple clauses`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a != null && a % 2 == 0 -> println(2 + a)
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does not report when the parameter is checked on non-nullity with an else statement`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a != null -> println(2 + a)
                                else -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does not report on nullable type matching`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a !is Int -> println("a is null")
                            }
                        }

                        fun fizz(b: Int?) {
                            when {
                                b is Int? -> println("b is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does report on non-null type matching`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a is Int -> println(2 + a)
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does report on non-null type matching with multiple clauses`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a is Int && a % 2 == 0 -> println(2 + a)
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does not report on non-null type matching with an else statement`() {
                    val code = """
                        fun foo(a: Int?) {
                            when {
                                a is Int -> println(2 + a)
                                else -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }
            }

            @Nested
            inner class `with a subject` {
                @Test
                fun `does not report when the parameter is checked on nullity`() {
                    val code = """
                        fun foo(a: Int?) {
                            when (a) {
                                null -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does not report on nullable type matching`() {
                    val code = """
                        fun foo(a: Int?) {
                            when (a) {
                                !is Int -> println("a is null")
                            }
                        }

                        fun fizz(b: Int?) {
                            when (b) {
                                is Int? -> println("b is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }

                @Test
                fun `does report on non-null type matching`() {
                    val code = """
                        fun foo(a: Int?) {
                            when(a) {
                                is Int -> println(2 + a)
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
                }

                @Test
                fun `does not report on non-null type matching with an else statement`() {
                    val code = """
                        fun foo(a: Int?) {
                            when(a) {
                                is Int -> println(2 + a)
                                else -> println("a is null")
                            }
                        }
                    """.trimIndent()
                    assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
                }
            }
        }

        @Nested
        inner class `if-statements` {
            @Test
            fun `does not report when the parameter is checked on nullity`() {
                val code = """
                    fun foo(a: Int?) {
                        if (a == null) {
                            println("'a' is null")
                        }
                    }

                    fun fizz(a: Int?) {
                        if (null == a) {
                            println("'a' is null")
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }

            @Test
            fun `does not report when the if-check is in the else statement`() {
                val code = """
                    fun foo(num: Int, a: Int?) {
                        if (num % 2 == 0) {
                            println("'num' is even")
                        } else if (a == null) {
                            println("'a' is null")
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }

            @Test
            fun `does report when the parameter is only checked on non-nullity in a function`() {
                val code = """
                    fun foo(a: Int?) {
                        if (a != null) {
                            println(a + 5)
                        }
                    }

                    fun fizz(a: Int?) {
                        if (null != a) {
                            println(a + 5)
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).hasSize(2)
            }

            @Test
            fun `does report when the parameter is only checked on non-nullity with multiple clauses`() {
                val code = """
                    fun foo(a: Int?, other: Int) {
                        if (a != null && other % 2 == 0) {
                            println(a + 5)
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).hasSize(1)
            }

            @Test
            fun `does not report when the parameter is checked on non-nullity with an else statement`() {
                val code = """
                    fun foo(a: Int?) {
                        if (a != null) {
                            println(a + 5)
                        } else {
                            println(5)
                        }
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }

            @Test
            fun `does not report when there are other expressions after the non-null check`() {
                val code = """
                    fun foo(a: Int?) {
                        if (a != null) {
                            println(a + 5)
                        }
                        val b = 5 + 2
                    }
                """.trimIndent()
                assertThat(subject.compileAndLintWithContext(env, code)).isEmpty()
            }
        }
    }
}