[K2] Refactor: extract conditions in FirExpectConsistencyChecker

...to separate methods.

After the change each diagnostic report has its own condition,
independent from others, so you don't have to keep in mind
"we're in else branch, so this is already not a FirConstructor
and also it either top-level or inside classs".
This makes changes in next commits more clear and verifiable.

`isTopLevelOrInsideClass` condition for
`getConstructorDelegationCall` is not needed, because
constructor is always inside class.

^KT-59899

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirExpectConsistencyChecker.kt

@@ -15,6 +15,7 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.hasBody
 import org.jetbrains.kotlin.fir.declarations.utils.isExpect
 import org.jetbrains.kotlin.fir.declarations.utils.visibility
+import org.jetbrains.kotlin.fir.expressions.FirDelegatedConstructorCall
 
 // See old FE's [DeclarationsChecker]
 object FirExpectConsistencyChecker : FirBasicDeclarationChecker() {
@@ -24,7 +25,7 @@ object FirExpectConsistencyChecker : FirBasicDeclarationChecker() {
 
         val isTopLevel = context.containingDeclarations.size == 1
         val lastClass = context.containingDeclarations.lastOrNull() as? FirClass
-        val isInsideClass = lastClass != null
+        val isTopLevelOrInsideClass = isTopLevel || lastClass != null
 
         if (declaration is FirAnonymousInitializer) {
             if (lastClass?.isExpect == true) {
@@ -33,27 +34,41 @@ object FirExpectConsistencyChecker : FirBasicDeclarationChecker() {
             return
         }
 
-        if (
+        if (declaration !is FirMemberDeclaration || !declaration.isExpect) {
-            declaration !is FirMemberDeclaration ||
-            !isTopLevel && !isInsideClass ||
-            !declaration.isExpect
-        ) {
             return
         }
 
-        if (declaration is FirConstructor) {
+        getConstructorDelegationCall(declaration)?.let { delegatedConstructor ->
-            if (!declaration.isPrimary) {
+            reporter.reportOn(delegatedConstructor.source, FirErrors.EXPECTED_CLASS_CONSTRUCTOR_DELEGATION_CALL, context)
-                val delegatedConstructorSource = declaration.delegatedConstructor?.source
+        }
-                if (delegatedConstructorSource?.kind !is KtFakeSourceElementKind) {
+
-                    reporter.reportOn(delegatedConstructorSource, FirErrors.EXPECTED_CLASS_CONSTRUCTOR_DELEGATION_CALL, context)
+        if (isProhibitedPrivateDeclaration(declaration, isTopLevelOrInsideClass)) {
-                }
-            }
-        } else if (Visibilities.isPrivate(declaration.visibility)) {
             reporter.reportOn(source, FirErrors.EXPECTED_PRIVATE_DECLARATION, context)
         }
 
-        if (declaration is FirFunction && declaration.hasBody) {
+        if (isProhibitedDeclarationWithBody(declaration, isTopLevelOrInsideClass)) {
             reporter.reportOn(source, FirErrors.EXPECTED_DECLARATION_WITH_BODY, context)
         }
     }
+
+    private fun getConstructorDelegationCall(declaration: FirMemberDeclaration): FirDelegatedConstructorCall? {
+        if (declaration is FirConstructor) {
+            if (!declaration.isPrimary) {
+                val delegatedConstructor = declaration.delegatedConstructor
+                val delegatedConstructorSource = delegatedConstructor?.source
+                if (delegatedConstructorSource?.kind !is KtFakeSourceElementKind) {
+                    return delegatedConstructor
+                }
+            }
+        }
+        return null
+    }
+
+    private fun isProhibitedPrivateDeclaration(declaration: FirMemberDeclaration, isTopLevelOrInsideClass: Boolean): Boolean {
+        return isTopLevelOrInsideClass && declaration !is FirConstructor && Visibilities.isPrivate(declaration.visibility)
+    }
+
+    private fun isProhibitedDeclarationWithBody(declaration: FirMemberDeclaration, isTopLevelOrInsideClass: Boolean): Boolean {
+        return isTopLevelOrInsideClass && declaration is FirFunction && declaration.hasBody
+    }
 }