FIR checker: refactor FirSyntaxChecker

Introduce a new checkPsiOrLightTree so the structure is more symmetric.
In addition, now implementation of `checkLightTree` has access to
`FirLightSourceElement` rather tha a generic `FirSourceElement`

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

@@ -27,7 +27,7 @@ object RedundantModalityModifierSyntaxChecker : FirDeclarationSyntaxChecker<FirD
     override fun isApplicable(element: FirDeclaration, source: FirSourceElement): Boolean =
         source.kind !is FirFakeSourceElementKind && element is FirMemberDeclaration
 
-    override fun checkLightTree(
+    override fun checkPsiOrLightTree(
         element: FirDeclaration,
         source: FirSourceElement,
         context: CheckerContext,

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

@@ -33,7 +33,7 @@ import org.jetbrains.kotlin.psi.KtDeclaration
 
 object RedundantVisibilityModifierSyntaxChecker : FirDeclarationSyntaxChecker<FirDeclaration, KtDeclaration>() {
 
-    override fun checkLightTree(
+    override fun checkPsiOrLightTree(
         element: FirDeclaration,
         source: FirSourceElement,
         context: CheckerContext,

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirAnonymousFunctionSyntaxChecker.kt

@@ -5,8 +5,8 @@
 
 package org.jetbrains.kotlin.fir.analysis.checkers.syntax
 
+import org.jetbrains.kotlin.fir.FirLightSourceElement
 import org.jetbrains.kotlin.fir.FirPsiSourceElement
-import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
@@ -34,7 +34,7 @@ object FirAnonymousFunctionSyntaxChecker : FirDeclarationSyntaxChecker<FirAnonym
 
     override fun checkLightTree(
         element: FirAnonymousFunction,
-        source: FirSourceElement,
+        source: FirLightSourceElement,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirCommaInWhenConditionChecker.kt

@@ -23,7 +23,7 @@ object FirCommaInWhenConditionChecker : FirExpressionSyntaxChecker<FirWhenExpres
         return element.subject == null
     }
 
-    override fun checkLightTree(
+    override fun checkPsiOrLightTree(
         element: FirWhenExpression,
         source: FirSourceElement,
         context: CheckerContext,

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirConfusingWhenBranchSyntaxChecker.kt

@@ -35,7 +35,7 @@ object FirConfusingWhenBranchSyntaxChecker : FirExpressionSyntaxChecker<FirWhenE
 
     override fun checkLightTree(
         element: FirWhenExpression,
-        source: FirSourceElement,
+        source: FirLightSourceElement,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirDelegationInInterfaceSyntaxChecker.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.syntax
 
 import org.jetbrains.kotlin.KtNodeTypes
+import org.jetbrains.kotlin.fir.FirLightSourceElement
 import org.jetbrains.kotlin.fir.FirPsiSourceElement
 import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
@@ -39,7 +40,7 @@ object FirDelegationInInterfaceSyntaxChecker : FirDeclarationSyntaxChecker<FirRe
 
     override fun checkLightTree(
         element: FirRegularClass,
-        source: FirSourceElement,
+        source: FirLightSourceElement,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirExplicitApiDeclarationChecker.kt

@@ -9,9 +9,7 @@ import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.config.AnalysisFlags
 import org.jetbrains.kotlin.config.ExplicitApiMode
 import org.jetbrains.kotlin.descriptors.ClassKind
-import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
-import org.jetbrains.kotlin.fir.FirRealSourceElementKind
-import org.jetbrains.kotlin.fir.FirSourceElement
+import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.isLocalMember
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
@@ -23,7 +21,6 @@ import org.jetbrains.kotlin.fir.declarations.impl.FirPrimaryConstructor
 import org.jetbrains.kotlin.fir.declarations.utils.effectiveVisibility
 import org.jetbrains.kotlin.fir.declarations.utils.isData
 import org.jetbrains.kotlin.fir.declarations.utils.isOverride
-import org.jetbrains.kotlin.fir.languageVersionSettings
 import org.jetbrains.kotlin.fir.resolve.transformers.publishedApiEffectiveVisibility
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.KtDeclaration
@@ -32,7 +29,12 @@ object FirExplicitApiDeclarationChecker : FirDeclarationSyntaxChecker<FirDeclara
     private val codeFragmentTypes =
         setOf(KtNodeTypes.BLOCK_CODE_FRAGMENT, KtNodeTypes.EXPRESSION_CODE_FRAGMENT, KtNodeTypes.TYPE_CODE_FRAGMENT)
 
-    override fun checkLightTree(element: FirDeclaration, source: FirSourceElement, context: CheckerContext, reporter: DiagnosticReporter) {
+    override fun checkPsiOrLightTree(
+        element: FirDeclaration,
+        source: FirSourceElement,
+        context: CheckerContext,
+        reporter: DiagnosticReporter
+    ) {
         if ((source.kind !is FirRealSourceElementKind && source.kind != FirFakeSourceElementKind.PropertyFromParameter) ||
             element !is FirMemberDeclaration
         ) {
@@ -143,4 +145,4 @@ object FirExplicitApiDeclarationChecker : FirDeclarationSyntaxChecker<FirDeclara
         // If current declaration is local or it's a member in a local declaration (local class, etc), then we do not require return type.
         return !declaration.isLocalMember && context.containingDeclarations.lastOrNull()?.isLocalMember != true
     }
-}
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirFunctionTypeParametersSyntaxChecker.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.syntax
 
 import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
+import org.jetbrains.kotlin.fir.FirLightSourceElement
 import org.jetbrains.kotlin.fir.FirPsiSourceElement
 import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
@@ -39,7 +40,7 @@ object FirFunctionTypeParametersSyntaxChecker : FirDeclarationSyntaxChecker<FirS
 
     override fun checkLightTree(
         element: FirSimpleFunction,
-        source: FirSourceElement,
+        source: FirLightSourceElement,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirLocalVariableTypeParametersSyntaxChecker.kt

@@ -6,16 +6,13 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.syntax
 
 import org.jetbrains.kotlin.config.LanguageFeature
-import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
-import org.jetbrains.kotlin.fir.FirPsiSourceElement
-import org.jetbrains.kotlin.fir.FirSourceElement
+import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.analysis.diagnostics.typeParametersList
 import org.jetbrains.kotlin.fir.declarations.FirProperty
-import org.jetbrains.kotlin.fir.languageVersionSettings
 import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.psi.KtProperty
 
@@ -41,7 +38,7 @@ object FirLocalVariableTypeParametersSyntaxChecker : FirDeclarationSyntaxChecker
 
     override fun checkLightTree(
         element: FirProperty,
-        source: FirSourceElement,
+        source: FirLightSourceElement,
         context: CheckerContext,
         reporter: DiagnosticReporter
     ) {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirSyntaxChecker.kt

@@ -18,7 +18,10 @@ import org.jetbrains.kotlin.fir.declarations.FirDeclaration
 import org.jetbrains.kotlin.fir.expressions.FirStatement
 
 /**
- * Checker that heavily relies on source tree. So it should have different implementation for each tree variant
+ * Checker that heavily relies on source tree. So it may have different implementation for each tree variant. Subclass should either
+ *
+ * - implement `checkPsiOrLightTree` in an AST-agnostic manner, or
+ * - implement both `checkPsi` and `checkLightTree` if it's difficult to handle PSI and LT tree in a unified way.
  */
 interface FirSyntaxChecker<in D : FirElement, P : PsiElement> {
 
@@ -34,18 +37,18 @@ interface FirSyntaxChecker<in D : FirElement, P : PsiElement> {
 
     fun isApplicable(element: D, source: FirSourceElement): Boolean = true
 
-    /**
-     *  By default psi tree should be equivalent to light tree and can be processed the same way
-     */
     fun checkPsi(element: D, source: FirPsiSourceElement, psi: P, context: CheckerContext, reporter: DiagnosticReporter) {
-        checkLightTree(element, source, context, reporter)
+        checkPsiOrLightTree(element, source, context, reporter)
     }
 
-    /*
-        accepts FirSourceElement instead of FirLightSourceElement because now they have the same interface
-        and it allows to reuse LT check for psi tree
+    fun checkLightTree(element: D, source: FirLightSourceElement, context: CheckerContext, reporter: DiagnosticReporter) {
+        checkPsiOrLightTree(element, source, context, reporter)
+    }
+
+    /**
+     *  By default psi tree should be equivalent to light tree and can be processed the same way.
      */
-    fun checkLightTree(element: D, source: FirSourceElement, context: CheckerContext, reporter: DiagnosticReporter)
+    fun checkPsiOrLightTree(element: D, source: FirSourceElement, context: CheckerContext, reporter: DiagnosticReporter) {}
 }
 
 abstract class FirDeclarationSyntaxChecker<in D : FirDeclaration, P : PsiElement> :

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirTypeParameterSyntaxChecker.kt

@@ -35,7 +35,7 @@ object FirTypeParameterSyntaxChecker : FirDeclarationSyntaxChecker<FirTypeParame
         }
     }
 
-    override fun checkLightTree(
+    override fun checkPsiOrLightTree(
         element: FirTypeParameter,
         source: FirSourceElement,
         context: CheckerContext,