Add PropertyUsedBeforeDeclaration rule (#6062)

detekt-core/src/main/resources/default-detekt-config.yml

@@ -475,6 +475,8 @@ potential-bugs:
     active: false
   NullableToStringCall:
     active: false
+  PropertyUsedBeforeDeclaration:
+    active: false
   UnconditionalJumpStatementInLoop:
     active: false
   UnnecessaryNotNullCheck:

detekt-rules-errorprone/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/PotentialBugProvider.kt

@@ -52,7 +52,8 @@ class PotentialBugProvider : DefaultRuleSetProvider {
             UnreachableCatchBlock(config),
             CastToNullableType(config),
             CastNullableToNonNullableType(config),
-            UnusedUnaryOperator(config)
+            UnusedUnaryOperator(config),
+            PropertyUsedBeforeDeclaration(config),
         )
     )
 }

detekt-rules-errorprone/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/PropertyUsedBeforeDeclaration.kt

@@ -0,0 +1,89 @@
+package io.gitlab.arturbosch.detekt.rules.bugs
+
+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.internal.RequiresTypeResolution
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.psi.KtClassOrObject
+import org.jetbrains.kotlin.psi.KtNameReferenceExpression
+import org.jetbrains.kotlin.psi.KtProperty
+import org.jetbrains.kotlin.psi.psiUtil.forEachDescendantOfType
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.util.getResolvedCall
+import org.jetbrains.kotlin.utils.addIfNotNull
+
+/**
+ * Reports properties that are used before declaration.
+ *
+ * <noncompliant>
+ * class C {
+ *     private val number
+ *         get() = if (isValid) 1 else 0
+ *
+ *     val list = listOf(number)
+ *
+ *     private val isValid = true
+ * }
+ *
+ * fun main() {
+ *     println(C().list) // [0]
+ * }
+ * </noncompliant>
+ *
+ * <compliant>
+ * class C {
+ *     private val isValid = true
+ *
+ *     private val number
+ *         get() = if (isValid) 1 else 0
+ *
+ *     val list = listOf(number)
+ * }
+ *
+ * fun main() {
+ *     println(C().list) // [1]
+ * }
+ * </compliant>
+ */
+@RequiresTypeResolution
+class PropertyUsedBeforeDeclaration(config: Config = Config.empty) : Rule(config) {
+    override val issue = Issue(
+        javaClass.simpleName,
+        Severity.Defect,
+        "Properties before declaration should not be used.",
+        Debt.FIVE_MINS
+    )
+
+    override fun visitClassOrObject(classOrObject: KtClassOrObject) {
+        super.visitClassOrObject(classOrObject)
+
+        val classMembers = classOrObject.body?.children ?: return
+
+        val allProperties = classMembers.filterIsInstance<KtProperty>().mapNotNull {
+            val name = it.name ?: return@mapNotNull null
+            val descriptor = bindingContext[BindingContext.DECLARATION_TO_DESCRIPTOR, it] ?: return@mapNotNull null
+            name to descriptor
+        }.toMap()
+
+        val declaredProperties = mutableSetOf<DeclarationDescriptor>()
+
+        classMembers.forEach { member ->
+            member.forEachDescendantOfType<KtNameReferenceExpression> {
+                val property = allProperties[it.text]
+                if (property != null && property !in declaredProperties && property == it.descriptor()) {
+                    report(CodeSmell(issue, Entity.from(it), "'${it.text}' is before declaration."))
+                }
+            }
+            if (member is KtProperty) {
+                declaredProperties.addIfNotNull(allProperties[member.name])
+            }
+        }
+    }
+
+    private fun KtNameReferenceExpression.descriptor() = getResolvedCall(bindingContext)?.resultingDescriptor
+}

detekt-rules-errorprone/src/test/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/PropertyUsedBeforeDeclarationSpec.kt

@@ -0,0 +1,89 @@
+package io.gitlab.arturbosch.detekt.rules.bugs
+
+import io.gitlab.arturbosch.detekt.rules.KotlinCoreEnvironmentTest
+import io.gitlab.arturbosch.detekt.test.assertThat
+import io.gitlab.arturbosch.detekt.test.compileAndLintWithContext
+import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
+import org.junit.jupiter.api.Test
+
+@KotlinCoreEnvironmentTest
+class PropertyUsedBeforeDeclarationSpec(private val env: KotlinCoreEnvironment) {
+    private val subject = PropertyUsedBeforeDeclaration()
+
+    @Test
+    fun `used before declaration in getter`() {
+        val code = """
+            class C {
+                private val number get() = if (isValid) 1 else 0
+                val list = listOf(number)
+                private val isValid = true
+            }
+            fun main() {
+                println(C().list) // [0]
+            }
+        """.trimIndent()
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).hasSize(1)
+        assertThat(findings).hasTextLocations(45 to 52)
+        assertThat(findings.first()).hasMessage("'isValid' is before declaration.")
+    }
+
+    @Test
+    fun `used before declaration in init`() {
+        val code = """
+            class C {
+                init {
+                    run {
+                        println(isValid) // false
+                    }
+                }
+                private val isValid = true
+            }
+            fun main() {
+                C()
+            }
+        """.trimIndent()
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).hasSize(1)
+    }
+
+    @Test
+    fun `used before declaration in function`() {
+        val code = """
+            class C {
+                fun f() = isValid
+                private val isValid = true
+            }
+        """.trimIndent()
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).hasSize(1)
+    }
+
+    @Test
+    fun `used after declaration in getter`() {
+        val code = """
+            class C {
+                private val isValid = true
+                private val number get() = if (isValid) 1 else 0
+                val list = listOf(number)
+            }
+        """.trimIndent()
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).isEmpty()
+    }
+
+    @Test
+    fun `variable shadowing`() {
+        val code = """
+            class C {
+                fun f(): Boolean  {
+                    val isValid = true 
+                    return isValid
+                }
+                private val isValid = true
+            }
+        """.trimIndent()
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).isEmpty()
+    }
+}