[FIR] Remove the redundant isFunctionType check

^KT-63865 fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFirTestdataTestGenerated.java

@@ -5266,6 +5266,12 @@ public class DiagnosticCompilerTestFirTestdataTestGenerated extends AbstractDiag
             runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/backingField.kt");
         }
 
+        @Test
+        @TestMetadata("castForFunctionsWithDifferentArities.kt")
+        public void testCastForFunctionsWithDifferentArities() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.kt");
+        }
+
         @Test
         @TestMetadata("classLiteralForParameter.kt")
         public void testClassLiteralForParameter() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFirTestDataTestGenerated.java

@@ -5266,6 +5266,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFirTestDataTestGenerated
             runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/backingField.kt");
         }
 
+        @Test
+        @TestMetadata("castForFunctionsWithDifferentArities.kt")
+        public void testCastForFunctionsWithDifferentArities() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.kt");
+        }
+
         @Test
         @TestMetadata("classLiteralForParameter.kt")
         public void testClassLiteralForParameter() throws Exception {

compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.fir.txt

@@ -0,0 +1,12 @@
+FILE: castForFunctionsWithDifferentArities.kt
+    public final fun test(b: R|kotlin/Boolean|, block1: R|kotlin/Any.() -> kotlin/Unit|, block2: R|(kotlin/Any.(kotlin/Any?) -> kotlin/Unit)?|): R|kotlin/Unit| {
+        when () {
+            R|<local>/b| ->  {
+                R|kotlin/requireNotNull|<R|kotlin/Any.() -> kotlin/Unit|>(R|<local>/block1|)
+            }
+            else ->  {
+                R|kotlin/requireNotNull|<R|kotlin/Any.(kotlin/Any?) -> kotlin/Unit|>(R|<local>/block2|)
+            }
+        }
+
+    }

compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.kt

@@ -0,0 +1,9 @@
+// ISSUE: KT-63865
+
+fun test(b: Boolean, block1: Any.() -> Unit, block2: (Any.(Any?) -> Unit)?) {
+    if (b) {
+        requireNotNull(block1)
+    } else {
+        requireNotNull(block2)
+    }
+}

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeDiagnosticsTestGenerated.java

@@ -5266,6 +5266,12 @@ public class FirLightTreeDiagnosticsTestGenerated extends AbstractFirLightTreeDi
             runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/backingField.kt");
         }
 
+        @Test
+        @TestMetadata("castForFunctionsWithDifferentArities.kt")
+        public void testCastForFunctionsWithDifferentArities() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.kt");
+        }
+
         @Test
         @TestMetadata("classLiteralForParameter.kt")
         public void testClassLiteralForParameter() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiDiagnosticTestGenerated.java

@@ -5266,6 +5266,12 @@ public class FirPsiDiagnosticTestGenerated extends AbstractFirPsiDiagnosticTest
             runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/backingField.kt");
         }
 
+        @Test
+        @TestMetadata("castForFunctionsWithDifferentArities.kt")
+        public void testCastForFunctionsWithDifferentArities() throws Exception {
+            runTest("compiler/fir/analysis-tests/testData/resolveWithStdlib/castForFunctionsWithDifferentArities.kt");
+        }
+
         @Test
         @TestMetadata("classLiteralForParameter.kt")
         public void testClassLiteralForParameter() throws Exception {

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/ConeInferenceContext.kt

@@ -69,7 +69,7 @@ interface ConeInferenceContext : TypeSystemInferenceExtensionContext, ConeTypeCo
     ): SimpleTypeMarker {
         val attributesList = attributes?.filterIsInstanceTo<ConeAttribute<*>, MutableList<ConeAttribute<*>>>(mutableListOf())
         val coneAttributes: ConeAttributes = if (isExtensionFunction) {
-            require(constructor is ConeClassLikeLookupTag && constructor.isSomeFunctionType(session))
+            require(constructor is ConeClassLikeLookupTag)
             // We don't want to create new instance of ConeAttributes which
             //   contains only CompilerConeAttributes.ExtensionFunctionType
             //   to avoid memory consumption