UnnecessaryNotNullCheck: fix false negative with smart casted arguments

detekt-psi-utils/api/detekt-psi-utils.api

@@ -141,5 +141,7 @@ public final class io/gitlab/arturbosch/detekt/rules/TraversingKt {
 
 public final class io/gitlab/arturbosch/detekt/rules/TypeUtilsKt {
 	public static final fun fqNameOrNull (Lorg/jetbrains/kotlin/types/KotlinType;)Lorg/jetbrains/kotlin/name/FqName;
+	public static final fun getDataFlowAwareTypes (Lorg/jetbrains/kotlin/psi/KtExpression;Lorg/jetbrains/kotlin/resolve/BindingContext;Lorg/jetbrains/kotlin/config/LanguageVersionSettings;Lorg/jetbrains/kotlin/resolve/calls/smartcasts/DataFlowValueFactory;Lorg/jetbrains/kotlin/types/KotlinType;)Ljava/util/Set;
+	public static synthetic fun getDataFlowAwareTypes$default (Lorg/jetbrains/kotlin/psi/KtExpression;Lorg/jetbrains/kotlin/resolve/BindingContext;Lorg/jetbrains/kotlin/config/LanguageVersionSettings;Lorg/jetbrains/kotlin/resolve/calls/smartcasts/DataFlowValueFactory;Lorg/jetbrains/kotlin/types/KotlinType;ILjava/lang/Object;)Ljava/util/Set;
 }
 

detekt-psi-utils/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/TypeUtils.kt

@@ -1,10 +1,54 @@
 package io.gitlab.arturbosch.detekt.rules
 
+import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.psi.KtExpression
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowValueFactory
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameOrNull
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.TypeUtils
+import org.jetbrains.kotlin.util.containingNonLocalDeclaration
 
 fun KotlinType.fqNameOrNull(): FqName? {
     return TypeUtils.getClassDescriptor(this)?.fqNameOrNull()
 }
+
+/**
+ * Returns types considering data flow.
+ *
+ * For Example, for `s` in `print(s)` below, [BindingContext.getType] returns String?, but this function returns String.
+ *
+ * ```kotlin
+ * fun foo(s: String?) {
+ *     if (s != null) {
+ *         println(s) // s is String (smart cast from String?)
+ *     }
+ * }
+ * ```
+ */
+@Suppress("ReturnCount")
+fun KtExpression.getDataFlowAwareTypes(
+    bindingContext: BindingContext,
+    languageVersionSettings: LanguageVersionSettings,
+    dataFlowValueFactory: DataFlowValueFactory,
+    originalType: KotlinType? = bindingContext.getType(this),
+): Set<KotlinType> {
+    require(bindingContext != BindingContext.EMPTY) { "The bindingContext must not be empty" }
+
+    if (originalType == null) return emptySet()
+
+    val dataFlowInfo = bindingContext[BindingContext.EXPRESSION_TYPE_INFO, this]
+        ?.dataFlowInfo
+        ?: return setOf(originalType)
+
+    val containingDeclaration = containingNonLocalDeclaration()
+        ?.let { bindingContext[BindingContext.DECLARATION_TO_DESCRIPTOR, it] }
+        ?: return setOf(originalType)
+
+    val dataFlowValue = dataFlowValueFactory
+        .createDataFlowValue(this, originalType, bindingContext, containingDeclaration)
+
+    return dataFlowInfo.getStableTypes(dataFlowValue, languageVersionSettings)
+        .ifEmpty { setOf(originalType) }
+}

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

@@ -8,6 +8,7 @@ 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 io.gitlab.arturbosch.detekt.rules.getDataFlowAwareTypes
 import io.gitlab.arturbosch.detekt.rules.safeAs
 import org.jetbrains.kotlin.com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
@@ -20,7 +21,6 @@ import org.jetbrains.kotlin.psi.KtSafeQualifiedExpression
 import org.jetbrains.kotlin.psi.KtSimpleNameExpression
 import org.jetbrains.kotlin.psi.KtStringTemplateEntry
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
-import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.calls.util.getResolvedCall
 import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameOrNull
 import org.jetbrains.kotlin.types.isFlexible
@@ -86,21 +86,21 @@ class NullableToStringCall(config: Config = Config.empty) : Rule(config) {
     }
 
     private fun KtExpression.isNullable(): Boolean {
+        val compilerResources = compilerResources ?: return false
+
         val safeAccessOperation = safeAs<KtSafeQualifiedExpression>()?.operationTokenNode?.safeAs<PsiElement>()
         if (safeAccessOperation != null) {
             return bindingContext.diagnostics.forElement(safeAccessOperation).none {
                 it.factory == Errors.UNNECESSARY_SAFE_CALL
             }
         }
-        val compilerResources = compilerResources ?: return false
-        val descriptor = descriptor() ?: return false
-        val originalType = descriptor.returnType ?.takeIf { it.isNullable() && !it.isFlexible() } ?: return false
-        val dataFlowInfo =
-            bindingContext[BindingContext.EXPRESSION_TYPE_INFO, this]?.dataFlowInfo ?: return false
-        val dataFlowValue =
-            compilerResources.dataFlowValueFactory.createDataFlowValue(this, originalType, bindingContext, descriptor)
-        val dataFlowTypes =
-            dataFlowInfo.getStableTypes(dataFlowValue, compilerResources.languageVersionSettings)
+        val originalType = descriptor()?.returnType?.takeIf { it.isNullable() && !it.isFlexible() } ?: return false
+        val dataFlowTypes = getDataFlowAwareTypes(
+            bindingContext,
+            compilerResources.languageVersionSettings,
+            compilerResources.dataFlowValueFactory,
+            originalType
+        )
         return dataFlowTypes.all { it.isNullable() }
     }
 

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

@@ -8,15 +8,11 @@ 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 io.gitlab.arturbosch.detekt.rules.getDataFlowAwareTypes
 import io.gitlab.arturbosch.detekt.rules.isCalling
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.KtCallExpression
-import org.jetbrains.kotlin.psi.KtExpression
-import org.jetbrains.kotlin.psi.psiUtil.getCallNameExpression
-import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.calls.util.getType
-import org.jetbrains.kotlin.types.typeUtil.TypeNullability
-import org.jetbrains.kotlin.types.typeUtil.nullability
+import org.jetbrains.kotlin.types.isNullable
 
 /**
  * Reports unnecessary not-null checks with `requireNotNull` or `checkNotNull` that can be removed by the user.
@@ -41,30 +37,37 @@ class UnnecessaryNotNullCheck(config: Config = Config.empty) : Rule(config) {
         Debt.FIVE_MINS,
     )
 
+    @Suppress("ReturnCount")
     override fun visitCallExpression(expression: KtCallExpression) {
         super.visitCallExpression(expression)
 
-        if (bindingContext == BindingContext.EMPTY) return
+        val compilerResources = compilerResources ?: return
 
-        if (expression.isCalling(requireNotNullFunctionFqName, bindingContext) ||
-            expression.isCalling(checkNotNullFunctionFqName, bindingContext)
-        ) {
-            val argument = expression.valueArguments[0].lastChild as KtExpression
-            if (argument.getType(bindingContext)?.nullability() == TypeNullability.NOT_NULL) {
-                val callName = expression.getCallNameExpression()?.text
-                report(
-                    CodeSmell(
-                        issue = issue,
-                        entity = Entity.from(expression),
-                        message = "Using `$callName` on non-null `${argument.text}` is unnecessary",
-                    )
-                )
-            }
-        }
+        val callee = expression.calleeExpression ?: return
+        val argument = expression.valueArguments.firstOrNull()?.getArgumentExpression() ?: return
+
+        if (!expression.isCalling(notNullCheckFunctionFqNames, bindingContext)) return
+
+        val dataFlowAwareTypes = argument.getDataFlowAwareTypes(
+            bindingContext,
+            compilerResources.languageVersionSettings,
+            compilerResources.dataFlowValueFactory
+        )
+        if (dataFlowAwareTypes.all { it.isNullable() }) return
+
+        report(
+            CodeSmell(
+                issue = issue,
+                entity = Entity.from(expression),
+                message = "Using `${callee.text}` on non-null `${argument.text}` is unnecessary",
+            )
+        )
     }
 
     companion object {
-        private val requireNotNullFunctionFqName = FqName("kotlin.requireNotNull")
-        private val checkNotNullFunctionFqName = FqName("kotlin.checkNotNull")
+        private val notNullCheckFunctionFqNames = listOf(
+            FqName("kotlin.requireNotNull"),
+            FqName("kotlin.checkNotNull"),
+        )
     }
 }

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

@@ -77,6 +77,32 @@ class UnnecessaryNotNullCheckSpec(private val env: KotlinCoreEnvironment) {
             assertThat(findings).hasSize(1)
             assertThat(findings).hasTextLocations(16 to 58)
         }
+
+        @Test
+        fun shouldDetectAfterNullCheck() {
+            val code = """
+                fun foo(x: Int?) {
+                    if (x != null) {
+                        requireNotNull(x)
+                    }
+                }
+            """.trimIndent()
+            val findings = subject.lintWithContext(env, code)
+            assertThat(findings).hasSize(1)
+        }
+
+        @Test
+        fun shouldDetectAfterTypeCheck() {
+            val code = """
+                fun bar(x: Any?) {
+                    if (x is String) {
+                        requireNotNull(x)
+                    }
+                }
+            """.trimIndent()
+            val findings = subject.lintWithContext(env, code)
+            assertThat(findings).hasSize(1)
+        }
     }
 
     @Nested