Fixed duplication of some generic functions in code completion

core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt

@@ -97,3 +97,9 @@ public fun JetType.isArrayOfJavaLangClass(): Boolean =
         KotlinBuiltIns.isArray(this) && getArguments().firstOrNull()?.getType()?.isJavaLangClass() ?: false
 
 public fun JetType.isJavaLangClassOrArray(): Boolean = isJavaLangClass() || isArrayOfJavaLangClass()
+
+public fun JetTypeChecker.equalTypesOrNulls(type1: JetType?, type2: JetType?): Boolean {
+    if (type1 identityEquals type2) return true
+    if (type1 == null || type2 == null) return false
+    return equalTypes(type1, type2)
+}

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/CompletionUtils.kt

@@ -29,7 +29,6 @@ import org.jetbrains.kotlin.idea.caches.resolve.ResolutionFacade
 import org.jetbrains.kotlin.idea.completion.handlers.CastReceiverInsertHandler
 import org.jetbrains.kotlin.idea.completion.handlers.WithTailInsertHandler
 import org.jetbrains.kotlin.idea.util.FuzzyType
-import org.jetbrains.kotlin.idea.util.fuzzyReturnType
 import org.jetbrains.kotlin.idea.util.getImplicitReceiversWithInstance
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
@@ -39,6 +38,9 @@ import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.inline.InlineUtil
+import org.jetbrains.kotlin.types.TypeConstructor
+import org.jetbrains.kotlin.types.checker.JetTypeChecker
+import org.jetbrains.kotlin.types.typeUtil.equalTypesOrNulls
 import java.util.ArrayList
 
 enum class ItemPriority {
@@ -144,12 +146,28 @@ fun descriptorsEqualWithSubstitution(descriptor1: DeclarationDescriptor?, descri
     // optimization:
     if (descriptor1 == descriptor1.getOriginal() && descriptor2 == descriptor2.getOriginal()) return true
 
-    if (descriptor1.getReturnType() != descriptor2.getReturnType()) return false
+    val typeChecker = JetTypeChecker.withAxioms(object: JetTypeChecker.TypeConstructorEquality {
+        override fun equals(a: TypeConstructor, b: TypeConstructor): Boolean {
+            val typeParam1 = a.getDeclarationDescriptor() as? TypeParameterDescriptor
+            val typeParam2 = b.getDeclarationDescriptor() as? TypeParameterDescriptor
+            if (typeParam1 != null
+                && typeParam2 != null
+                && typeParam1.getContainingDeclaration() == descriptor1
+                && typeParam2.getContainingDeclaration() == descriptor2) {
+                return typeParam1.getIndex() == typeParam2.getIndex()
+            }
+
+            return a == b
+        }
+    })
+
+    if (!typeChecker.equalTypesOrNulls(descriptor1.getReturnType(), descriptor2.getReturnType())) return false
+
     val parameters1 = descriptor1.getValueParameters()
     val parameters2 = descriptor2.getValueParameters()
     if (parameters1.size() != parameters2.size()) return false
-    for (i in parameters1.indices) {
-        if (parameters1[i].getType() != parameters2[i].getType()) return false
+    for ((param1, param2) in parameters1.zip(parameters2)) {
+        if (!typeChecker.equalTypes(param1.getType(), param2.getType())) return false
     }
     return true
 }

idea/idea-completion/testData/basic/multifile/NoGenericFunDuplication/NoGenericFunDuplication.dependency.kt

@@ -0,0 +1,5 @@
+package dependency
+
+class MyPair<A, B>(public val first: A, public val second: B)
+
+public fun <A, B> A.pair(that: B): MyPair<A, B> = MyPair(this, that)

idea/idea-completion/testData/basic/multifile/NoGenericFunDuplication/NoGenericFunDuplication.kt

@@ -0,0 +1,9 @@
+// this test tests correct substitution equality checking for generic functions
+import dependency.pair
+
+fun foo() {
+    1 pai<caret>
+}
+
+// EXIST: pair
+// NUMBER: 1

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/MultiFileJvmBasicCompletionTestGenerated.java

@@ -131,6 +131,12 @@ public class MultiFileJvmBasicCompletionTestGenerated extends AbstractMultiFileJ
         doTest(fileName);
     }
 
+    @TestMetadata("NoGenericFunDuplication")
+    public void testNoGenericFunDuplication() throws Exception {
+        String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/multifile/NoGenericFunDuplication/");
+        doTest(fileName);
+    }
+
     @TestMetadata("NotImportedExtensionForImplicitReceiver")
     public void testNotImportedExtensionForImplicitReceiver() throws Exception {
         String fileName = JetTestUtils.navigationMetadata("idea/idea-completion/testData/basic/multifile/NotImportedExtensionForImplicitReceiver/");