[FIR] Cleanup and refactoring for checkers

compiler/fir/analysis-tests/testData/extendedCheckers/RedundantModalityModifierChecker.kt

@@ -1,12 +1,22 @@
+object O {
+    fun foo() {}
+}
+
 // Interface
 interface Interface {
-    // Redundant
+    // Questionable cuz compiler reports warning here in FE 1.0
     <!REDUNDANT_MODALITY_MODIFIER!>open<!> val gav: Int
         get() = 42
     // Redundant
     <!REDUNDANT_MODALITY_MODIFIER!>abstract<!> fun foo()
-    // Redundant
-    private <!REDUNDANT_MODALITY_MODIFIER!>final<!> fun bar() {}
+    // error
+    private final fun bar() {}
+
+    <!REDUNDANT_MODALITY_MODIFIER!>open<!> fun goo() {}
+    <!REDUNDANT_MODALITY_MODIFIER!>abstract<!> fun tar()
+
+    // error
+    abstract fun too() {}
 }
 interface B {
     <!REDUNDANT_MODALITY_MODIFIER!>abstract<!> var bar: Unit
@@ -51,8 +61,8 @@ open class OpenDerived : Base() {
 interface Derived : Interface {
     // Redundant
     override <!REDUNDANT_MODALITY_MODIFIER!>open<!> fun foo() {}
-    // Redundant
-    <!REDUNDANT_MODALITY_MODIFIER!>final<!> class Nested
+    // error
+    final class Nested
 }
 // Derived abstract class
 abstract class AbstractDerived1(override final val gav: Int) : Interface {

compiler/fir/analysis-tests/testData/extendedCheckers/RedundantModalityModifierChecker.txt

@@ -1,4 +1,13 @@
 FILE: RedundantModalityModifierChecker.kt
+    public final object O : R|kotlin/Any| {
+        private constructor(): R|O| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final fun foo(): R|kotlin/Unit| {
+        }
+
+    }
     public abstract interface Interface : R|kotlin/Any| {
         public open val gav: R|kotlin/Int|
             public get(): R|kotlin/Int| {
@@ -10,6 +19,14 @@ FILE: RedundantModalityModifierChecker.kt
         private final fun bar(): R|kotlin/Unit| {
         }
 
+        public open fun goo(): R|kotlin/Unit| {
+        }
+
+        public abstract fun tar(): R|kotlin/Unit|
+
+        public abstract fun too(): R|kotlin/Unit| {
+        }
+
     }
     public abstract interface B : R|kotlin/Any| {
         public abstract var bar: R|kotlin/Unit|

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantExplicitTypeChecker.kt

@@ -22,7 +22,6 @@ import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.types.classId
 import org.jetbrains.kotlin.fir.types.coneType
-import org.jetbrains.kotlin.fir.types.impl.FirResolvedTypeRefImpl
 import org.jetbrains.kotlin.name.ClassId
 
 object RedundantExplicitTypeChecker : FirMemberDeclarationChecker() {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantModalityModifierChecker.kt

@@ -6,12 +6,14 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.extended
 
 import com.intellij.psi.impl.source.tree.LeafPsiElement
+import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.fir.FirFakeSourceElement
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirMemberDeclarationChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.implicitModality
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.REDUNDANT_MODALITY_MODIFIER
+import org.jetbrains.kotlin.fir.declarations.FirClass
 import org.jetbrains.kotlin.fir.declarations.FirMemberDeclaration
 import org.jetbrains.kotlin.fir.psi
 import org.jetbrains.kotlin.fir.toFirPsiSourceElement
@@ -26,6 +28,11 @@ object RedundantModalityModifierChecker : FirMemberDeclarationChecker() {
 
         val modalityModifier = (declaration.psi as? KtDeclaration)?.modalityModifier() ?: return
         val modality = (modalityModifier as? LeafPsiElement)?.elementType as? KtModifierKeywordToken ?: return
+        if (
+            modality == KtTokens.FINAL_KEYWORD
+            && (context.containingDeclarations.last() as? FirClass<*>)?.classKind == ClassKind.INTERFACE
+        ) return
+
         val implicitModality = declaration.implicitModality(context)
 
         if (modality != implicitModality) return

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantVisibilityModifierChecker.kt

@@ -26,7 +26,7 @@ object RedundantVisibilityModifierChecker : FirBasicDeclarationChecker() {
         if (declaration.source is FirFakeSourceElement<*>) return
         if (
             declaration !is FirMemberDeclaration
-            && !(declaration is FirPropertyAccessor && declaration.visibility == context.lastInContainingDeclarationsVisibility)
+            && !(declaration is FirPropertyAccessor && declaration.visibility == context.containingPropertyVisibility)
         ) return
 
         val modifierList = (declaration.source.getModifierList() as? FirPsiModifierList)?.modifierList ?: return
@@ -122,6 +122,6 @@ object RedundantVisibilityModifierChecker : FirBasicDeclarationChecker() {
             else -> false
         }
 
-    private val CheckerContext.lastInContainingDeclarationsVisibility
-        get() = (this.containingDeclarations.last() as FirProperty).visibility
+    private val CheckerContext.containingPropertyVisibility
+        get() = (this.containingDeclarations.last() as? FirProperty)?.visibility
 }