Do not report "no reflection" inspection where reflection is not used

#KT-7059 Fixed

compiler/frontend/src/org/jetbrains/kotlin/types/reflect/ReflectionTypes.kt

@@ -22,6 +22,8 @@ import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.name.isSubpackageOf
+import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.scopes.JetScope
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.TypeUtils.makeStarProjection
@@ -125,4 +127,12 @@ public class ReflectionTypes(private val module: ModuleDescriptor) {
         arguments.add(TypeProjectionImpl(returnType))
         return JetTypeImpl(annotations, classDescriptor.getTypeConstructor(), false, arguments, classDescriptor.getMemberScope(arguments))
     }
+
+    companion object {
+        public fun isReflectionType(type: JetType): Boolean {
+            val descriptor = type.getConstructor().getDeclarationDescriptor() ?: return false
+            val fqName = DescriptorUtils.getFqName(descriptor)
+            return fqName.isSafe() && fqName.toSafe().isSubpackageOf(KOTLIN_REFLECT_FQ_NAME)
+        }
+    }
 }

idea/src/org/jetbrains/kotlin/idea/inspections/ReflectionNotFoundInspection.kt

@@ -27,6 +27,7 @@ import com.intellij.openapi.vfs.VfsUtil
 import com.intellij.openapi.vfs.VfsUtilCore
 import com.intellij.psi.PsiElementVisitor
 import org.jetbrains.kotlin.idea.JetBundle
+import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.caches.resolve.findModuleDescriptor
 import org.jetbrains.kotlin.idea.configuration.ConfigureKotlinInProjectUtils
 import org.jetbrains.kotlin.idea.configuration.KotlinJavaModuleConfigurator
@@ -38,7 +39,9 @@ import org.jetbrains.kotlin.load.java.JvmAbi
 import org.jetbrains.kotlin.psi.JetDoubleColonExpression
 import org.jetbrains.kotlin.psi.JetFile
 import org.jetbrains.kotlin.psi.JetVisitorVoid
+import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.serialization.deserialization.findClassAcrossModuleDependencies
+import org.jetbrains.kotlin.types.reflect.ReflectionTypes
 import org.jetbrains.kotlin.utils.PathUtil
 import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstanceOrNull
 import org.jetbrains.kotlin.utils.singletonOrEmptyList
@@ -49,7 +52,7 @@ public class ReflectionNotFoundInspection : AbstractKotlinInspection() {
 
     override fun buildVisitor(holder: ProblemsHolder, isOnTheFly: Boolean): PsiElementVisitor {
         val file = holder.getFile()
-        val reportProblem =
+        val noReflectionInClassPath =
                 file is JetFile &&
                 ProjectRootsUtil.isInProjectSource(file) &&
                 file.findModuleDescriptor().findClassAcrossModuleDependencies(JvmAbi.REFLECTION_FACTORY_IMPL) == null
@@ -70,14 +73,20 @@ public class ReflectionNotFoundInspection : AbstractKotlinInspection() {
             }
 
             override fun visitDoubleColonExpression(expression: JetDoubleColonExpression) {
-                if (reportProblem) {
-                    holder.registerProblem(
-                            expression.getDoubleColonTokenReference(),
-                            JetBundle.message("reflection.not.found"),
-                            ProblemHighlightType.GENERIC_ERROR_OR_WARNING,
-                            *(createQuickFix().singletonOrEmptyList().copyToArray())
-                    )
-                }
+                if (!noReflectionInClassPath) return
+
+                val expectedType = expression.analyze().get(BindingContext.EXPECTED_EXPRESSION_TYPE, expression)
+                if (expectedType != null && !ReflectionTypes.isReflectionType(expectedType)) return
+
+                // If a callable reference is used where a KFunction/KProperty/... expected, we should report that usage as dangerous
+                // because reflection features will fail without kotlin-reflect.jar in the classpath.
+                // If it's only used as a Function however (for example, "list.map(::function)"), we should not report anything
+                holder.registerProblem(
+                        expression.getDoubleColonTokenReference(),
+                        JetBundle.message("reflection.not.found"),
+                        ProblemHighlightType.GENERIC_ERROR_OR_WARNING,
+                        *(createQuickFix().singletonOrEmptyList().copyToArray())
+                )
             }
         }
     }

idea/testData/inspections/reflectionNotFound/functionReference.kt

@@ -0,0 +1,18 @@
+package test
+
+// WITH_RUNTIME
+
+import kotlin.reflect.KFunction0
+
+fun foo() {}
+
+fun bar(f: () -> Unit) = f()
+
+// Inspection should be reported here because '::foo' may be used as a reflection object
+val p1 = ::foo                    // the type is KFunction0 by default
+val p2: KFunction0<Unit> = ::foo  // the expected type is KFunction0
+
+// But shouldn't be reported here
+val p3 = bar(::foo)               // the expected type is Function0, '::foo' is used as an ordinary function
+val p4: Any = ::foo               // the expected type is Any
+val p5: UnresolvedClass = ::foo   // an error, another warning would be useless

idea/testData/inspections/reflectionNotFound/inspectionData/expected.xml

@@ -0,0 +1,18 @@
+<problems>
+  <problem>
+    <file>functionReference.kt</file>
+    <line>12</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/functionReference.kt" />
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Reflection not found</problem_class>
+    <description>Reflection not found in the classpath</description>
+  </problem>
+  <problem>
+    <file>functionReference.kt</file>
+    <line>13</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/functionReference.kt" />
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Reflection not found</problem_class>
+    <description>Reflection not found in the classpath</description>
+  </problem>
+</problems>

idea/testData/inspections/reflectionNotFound/inspectionData/inspections.test

@@ -0,0 +1 @@
+// INSPECTION_CLASS: org.jetbrains.kotlin.idea.inspections.ReflectionNotFoundInspection

idea/tests/org/jetbrains/kotlin/idea/codeInsight/JetInspectionTestGenerated.java

@@ -81,6 +81,12 @@ public class JetInspectionTestGenerated extends AbstractJetInspectionTest {
             JetTestUtils.assertAllTestsPresentInSingleGeneratedClass(this.getClass(), new File("idea/testData/inspections"), Pattern.compile("^(inspections\\.test)$"));
         }
 
+        @TestMetadata("reflectionNotFound/inspectionData/inspections.test")
+        public void testReflectionNotFound_inspectionData_Inspections_test() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/testData/inspections/reflectionNotFound/inspectionData/inspections.test");
+            doTest(fileName);
+        }
+
         @TestMetadata("spelling/inspectionData/inspections.test")
         public void testSpelling_inspectionData_Inspections_test() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("idea/testData/inspections/spelling/inspectionData/inspections.test");