diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirCallsEffectAnalyzer.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirCallsEffectAnalyzer.kt
index 1c648b8d3c3..b0cede828f4 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirCallsEffectAnalyzer.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirCallsEffectAnalyzer.kt
@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.cfa.FirControlFlowChecker
 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.contracts.FirContractDescription
 import org.jetbrains.kotlin.fir.contracts.coneEffects
 import org.jetbrains.kotlin.fir.contracts.description.ConeCallsEffectDeclaration
@@ -73,11 +74,9 @@ object FirCallsEffectAnalyzer : FirControlFlowChecker() {
         )
 
         for ((symbol, leakedPlaces) in leakedSymbols) {
-            function.contractDescription.source?.let {
-                reporter.report(FirErrors.LEAKED_IN_PLACE_LAMBDA.on(it, symbol), context)
-            }
+            reporter.reportOn(function.contractDescription.source, FirErrors.LEAKED_IN_PLACE_LAMBDA, symbol, context)
             leakedPlaces.forEach {
-                reporter.report(FirErrors.LEAKED_IN_PLACE_LAMBDA.on(it, symbol), context)
+                reporter.reportOn(it, FirErrors.LEAKED_IN_PLACE_LAMBDA, symbol, context)
             }
         }
 
@@ -111,10 +110,15 @@ object FirCallsEffectAnalyzer : FirControlFlowChecker() {
     ): Boolean {
         val foundRange = info[symbol] ?: EventOccurrencesRange.ZERO
         if (foundRange !in requiredRange) {
-            function.contractDescription.source?.let {
-                reporter.report(FirErrors.WRONG_INVOCATION_KIND.on(it, symbol, requiredRange, foundRange), context)
-                return true
-            }
+            reporter.reportOn(
+                function.contractDescription.source,
+                FirErrors.WRONG_INVOCATION_KIND,
+                symbol,
+                requiredRange,
+                foundRange,
+                context
+            )
+            return true
         }
         return false
     }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
index 2a7a6fbf7d0..b268d34555f 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirPropertyInitializationAnalyzer.kt
@@ -80,10 +80,8 @@ object FirPropertyInitializationAnalyzer : AbstractFirPropertyInitializationChec
             }
             val kind = info[symbol] ?: EventOccurrencesRange.ZERO
             if (symbol.fir.isVal && kind.canBeRevisited()) {
-                node.fir.lValue.source?.let {
-                    reporter.report(FirErrors.VAL_REASSIGNMENT.on(it, symbol), context)
-                    return true
-                }
+                reporter.reportOn(node.fir.lValue.source, FirErrors.VAL_REASSIGNMENT, symbol, context)
+                return true
             }
             return false
         }
@@ -109,10 +107,8 @@ object FirPropertyInitializationAnalyzer : AbstractFirPropertyInitializationChec
         ): Boolean {
             val kind = info[symbol] ?: EventOccurrencesRange.ZERO
             if (!kind.isDefinitelyVisited()) {
-                node.fir.source?.let {
-                    reporter.report(FirErrors.UNINITIALIZED_VARIABLE.on(it, symbol), context)
-                    return true
-                }
+                reporter.reportOn(node.fir.source, FirErrors.UNINITIALIZED_VARIABLE, symbol, context)
+                return true
             }
             return false
         }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirReturnsImpliesAnalyzer.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirReturnsImpliesAnalyzer.kt
index bd1f76c1106..d92b1fbe00b 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirReturnsImpliesAnalyzer.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirReturnsImpliesAnalyzer.kt
@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.isSupertypeOf
 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.contracts.FirResolvedContractDescription
 import org.jetbrains.kotlin.fir.contracts.coneEffects
 import org.jetbrains.kotlin.fir.contracts.description.*
@@ -63,9 +64,7 @@ object FirReturnsImpliesAnalyzer : FirControlFlowChecker() {
             }
 
             if (wrongCondition) {
-                function.contractDescription.source?.let {
-                    reporter.report(FirErrors.WRONG_IMPLIES_CONDITION.on(it), context)
-                }
+                reporter.reportOn(function.contractDescription.source, FirErrors.WRONG_IMPLIES_CONDITION, context)
             }
         }
     }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
index 07b343e54cd..71d959187fd 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirHelpers.kt
@@ -567,7 +567,7 @@ fun checkTypeMismatch(
         if (rValue.isNullLiteral && lValueType.nullability == ConeNullability.NOT_NULL) {
             reporter.reportOn(rValue.source, FirErrors.NULL_FOR_NONNULL_TYPE, context)
         } else {
-            reporter.report(diagnosticFactory.on(source, lValueType, rValueType), context)
+            reporter.reportOn(source, diagnosticFactory, lValueType, rValueType, context)
         }
     }
 }
@@ -617,4 +617,4 @@ fun extractTypeRefAndSourceFromTypeArgument(typeRef: FirTypeRef?, index: Int): P
     }
 
     return null
-}
\ No newline at end of file
+}
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirClassVarianceChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirClassVarianceChecker.kt
index eddacfb68bc..57ba73c4080 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirClassVarianceChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirClassVarianceChecker.kt
@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.extractTypeRefAndSourceFromTypeArgument
 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.declarations.*
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.toSymbol
@@ -116,14 +117,13 @@ object FirClassVarianceChecker : FirClassChecker() {
             ) {
                 val factory =
                     if (isInAbbreviation) FirErrors.TYPE_VARIANCE_CONFLICT_IN_EXPANDED_TYPE else FirErrors.TYPE_VARIANCE_CONFLICT
-                reporter.report(
-                    factory.on(
-                        resultSource,
-                        typeParameter.symbol,
-                        typeParameter.variance,
-                        variance,
-                        containingType
-                    ),
+                reporter.reportOn(
+                    resultSource,
+                    factory,
+                    typeParameter.symbol,
+                    typeParameter.variance,
+                    variance,
+                    containingType,
                     context
                 )
             }
@@ -167,4 +167,4 @@ object FirClassVarianceChecker : FirClassChecker() {
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirContractChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirContractChecker.kt
index 1b0c75b4052..87233a98f76 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirContractChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirContractChecker.kt
@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
 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.contracts.FirResolvedContractDescription
 import org.jetbrains.kotlin.fir.declarations.FirContractDescriptionOwner
 import org.jetbrains.kotlin.fir.declarations.FirFunction
@@ -30,7 +31,7 @@ object FirContractChecker : FirFunctionChecker() {
 
             // TODO: report on fine-grained locations, e.g., ... implies unresolved => report on unresolved, not the entire statement.
             //  but, sometimes, it's just reported on `contract`...
-            reporter.report(FirErrors.ERROR_IN_CONTRACT_DESCRIPTION.on(statement.source!!, UNEXPECTED_CONSTRUCTION), context)
+            reporter.reportOn(statement.source, FirErrors.ERROR_IN_CONTRACT_DESCRIPTION, UNEXPECTED_CONSTRUCTION, context)
         }
     }
 }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirInapplicableLateinitChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirInapplicableLateinitChecker.kt
index 8b2135c7b96..f3f781af572 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirInapplicableLateinitChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirInapplicableLateinitChecker.kt
@@ -9,6 +9,7 @@ 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
+import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyGetter
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertySetter
@@ -23,28 +24,28 @@ object FirInapplicableLateinitChecker : FirPropertyChecker() {
 
         when {
             declaration.isVal ->
-                reporter.reportOn(declaration.source, "is allowed only on mutable properties", context)
+                reporter.reportError(declaration.source, "is allowed only on mutable properties", context)
 
             declaration.initializer != null -> if (declaration.isLocal) {
-                reporter.reportOn(declaration.source, "is not allowed on local variables with initializer", context)
+                reporter.reportError(declaration.source, "is not allowed on local variables with initializer", context)
             } else {
-                reporter.reportOn(declaration.source, "is not allowed on properties with initializer", context)
+                reporter.reportError(declaration.source, "is not allowed on properties with initializer", context)
             }
 
             declaration.delegate != null ->
-                reporter.reportOn(declaration.source, "is not allowed on delegated properties", context)
+                reporter.reportError(declaration.source, "is not allowed on delegated properties", context)
 
             declaration.isNullable() ->
-                reporter.reportOn(declaration.source, "is not allowed on properties of a type with nullable upper bound", context)
+                reporter.reportError(declaration.source, "is not allowed on properties of a type with nullable upper bound", context)
 
             declaration.returnTypeRef.coneType.isPrimitiveOrNullablePrimitive -> if (declaration.isLocal) {
-                reporter.reportOn(declaration.source, "is not allowed on local variables of primitive types", context)
+                reporter.reportError(declaration.source, "is not allowed on local variables of primitive types", context)
             } else {
-                reporter.reportOn(declaration.source, "is not allowed on properties of primitive types", context)
+                reporter.reportError(declaration.source, "is not allowed on properties of primitive types", context)
             }
 
             declaration.hasGetter() || declaration.hasSetter() ->
-                reporter.reportOn(declaration.source, "is not allowed on properties with a custom getter or setter", context)
+                reporter.reportError(declaration.source, "is not allowed on properties with a custom getter or setter", context)
         }
     }
 
@@ -56,7 +57,7 @@ object FirInapplicableLateinitChecker : FirPropertyChecker() {
     private fun FirProperty.hasGetter() = getter != null && getter !is FirDefaultPropertyGetter
     private fun FirProperty.hasSetter() = setter != null && setter !is FirDefaultPropertySetter
 
-    private fun DiagnosticReporter.reportOn(source: FirSourceElement?, target: String, context: CheckerContext) {
-        source?.let { report(FirErrors.INAPPLICABLE_LATEINIT_MODIFIER.on(it, target), context) }
+    private fun DiagnosticReporter.reportError(source: FirSourceElement?, target: String, context: CheckerContext) {
+        reportOn(source, FirErrors.INAPPLICABLE_LATEINIT_MODIFIER, target, context)
     }
 }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMemberFunctionsChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMemberFunctionsChecker.kt
index 701fe180fce..451b8ed3adb 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMemberFunctionsChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMemberFunctionsChecker.kt
@@ -41,13 +41,16 @@ object FirMemberFunctionsChecker : FirRegularClassChecker() {
         val isAbstract = function.isAbstract || hasAbstractModifier
         if (isAbstract) {
             if (!containingDeclaration.canHaveAbstractDeclaration) {
-                reporter.report(
-                    FirErrors.ABSTRACT_FUNCTION_IN_NON_ABSTRACT_CLASS.on(source, function, containingDeclaration),
+                reporter.reportOn(
+                    source,
+                    FirErrors.ABSTRACT_FUNCTION_IN_NON_ABSTRACT_CLASS,
+                    function,
+                    containingDeclaration,
                     context
                 )
             }
             if (function.hasBody) {
-                reporter.report(FirErrors.ABSTRACT_FUNCTION_WITH_BODY.on(source, function), context)
+                reporter.reportOn(source, FirErrors.ABSTRACT_FUNCTION_WITH_BODY, function, context)
             }
         }
         val isInsideExpectClass = isInsideExpectClass(containingDeclaration, context)
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirModifierChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirModifierChecker.kt
index d164dad6716..0fb11bd9faa 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirModifierChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirModifierChecker.kt
@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.getModifierList
 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.declarations.*
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyAccessor
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
@@ -179,24 +180,24 @@ object FirModifierChecker : FirBasicDeclarationChecker() {
     private fun DiagnosticReporter.reportRepeatedModifier(
         modifier: FirModifier<*>, keyword: KtModifierKeywordToken, context: CheckerContext
     ) {
-        report(FirErrors.REPEATED_MODIFIER.on(modifier.source, keyword), context)
+        reportOn(modifier.source, FirErrors.REPEATED_MODIFIER, keyword, context)
     }
 
     private fun DiagnosticReporter.reportRedundantModifier(
         modifier: FirModifier<*>, firstKeyword: KtModifierKeywordToken, secondKeyword: KtModifierKeywordToken, context: CheckerContext
     ) {
-        report(FirErrors.REDUNDANT_MODIFIER.on(modifier.source, firstKeyword, secondKeyword), context)
+        reportOn(modifier.source, FirErrors.REDUNDANT_MODIFIER, firstKeyword, secondKeyword, context)
     }
 
     private fun DiagnosticReporter.reportDeprecatedModifierPair(
         modifier: FirModifier<*>, firstKeyword: KtModifierKeywordToken, secondKeyword: KtModifierKeywordToken, context: CheckerContext
     ) {
-        report(FirErrors.DEPRECATED_MODIFIER_PAIR.on(modifier.source, firstKeyword, secondKeyword), context)
+        reportOn(modifier.source, FirErrors.DEPRECATED_MODIFIER_PAIR, firstKeyword, secondKeyword, context)
     }
 
     private fun DiagnosticReporter.reportIncompatibleModifiers(
         modifier: FirModifier<*>, firstKeyword: KtModifierKeywordToken, secondKeyword: KtModifierKeywordToken, context: CheckerContext
     ) {
-        report(FirErrors.INCOMPATIBLE_MODIFIERS.on(modifier.source, firstKeyword, secondKeyword), context)
+        reportOn(modifier.source, FirErrors.INCOMPATIBLE_MODIFIERS, firstKeyword, secondKeyword, context)
     }
 }
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirOverrideChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirOverrideChecker.kt
index 10e557169f5..4a08424e0ad 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirOverrideChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirOverrideChecker.kt
@@ -242,10 +242,8 @@ object FirOverrideChecker : FirClassChecker() {
         overridden: FirCallableDeclaration<*>,
         context: CheckerContext
     ) {
-        overriding.source?.let { source ->
-            overridden.containingClass()?.let { containingClass ->
-                report(FirErrors.OVERRIDING_FINAL_MEMBER.on(source, overridden, containingClass.name), context)
-            }
+        overridden.containingClass()?.let { containingClass ->
+            reportOn(overriding.source, FirErrors.OVERRIDING_FINAL_MEMBER, overridden, containingClass.name, context)
         }
     }
 
@@ -254,7 +252,7 @@ object FirOverrideChecker : FirClassChecker() {
         overridden: FirMemberDeclaration,
         context: CheckerContext
     ) {
-        overriding.source?.let { report(FirErrors.VAR_OVERRIDDEN_BY_VAL.on(it, overriding, overridden), context) }
+        reportOn(overriding.source, FirErrors.VAR_OVERRIDDEN_BY_VAL, overriding, overridden, context)
     }
 
     private fun DiagnosticReporter.reportCannotWeakenAccessPrivilege(
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirFunctionReturnTypeMismatchChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirFunctionReturnTypeMismatchChecker.kt
index 735a4d02f65..31fc0a0f01c 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirFunctionReturnTypeMismatchChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirFunctionReturnTypeMismatchChecker.kt
@@ -35,7 +35,6 @@ object FirFunctionReturnTypeMismatchChecker : FirReturnExpressionChecker() {
         val returnExpressionType = resultExpression.typeRef.coneTypeSafe<ConeKotlinType>() ?: return
 
         if (!isSubtypeForTypeMismatch(typeContext, subtype = returnExpressionType, supertype = functionReturnType)) {
-            val returnExpressionSource = resultExpression.source ?: return
             if (resultExpression.isNullLiteral && functionReturnType.nullability == ConeNullability.NOT_NULL) {
                 reporter.reportOn(resultExpression.source, NULL_FOR_NONNULL_TYPE, context)
             } else {
@@ -51,12 +50,16 @@ object FirFunctionReturnTypeMismatchChecker : FirReturnExpressionChecker() {
                         context
                     )
                 } else {
-                    reporter.report(
-                        RETURN_TYPE_MISMATCH.on(returnExpressionSource, functionReturnType, returnExpressionType, targetElement),
+                    reporter.reportOn(
+                    resultExpression.source,
+                        RETURN_TYPE_MISMATCH,
+                    functionReturnType,
+                    returnExpressionType,
+                    targetElement,
                         context
                     )
                 }
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/DiagnosticReporter.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/DiagnosticReporter.kt
index 0a5bd2ff499..b9ae5e81991 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/DiagnosticReporter.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/DiagnosticReporter.kt
@@ -16,6 +16,7 @@ abstract class DiagnosticReporter {
     abstract fun report(diagnostic: FirDiagnostic<*>?, context: CheckerContext)
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 fun <P : PsiElement> DiagnosticReporter.reportOn(
     source: FirSourceElement?,
     factory: FirDiagnosticFactory0<P>,
@@ -24,6 +25,7 @@ fun <P : PsiElement> DiagnosticReporter.reportOn(
     source?.let { report(factory.on(it), context) }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 fun <P : PsiElement, A : Any> DiagnosticReporter.reportOn(
     source: FirSourceElement?,
     factory: FirDiagnosticFactory1<P, A>,
@@ -33,6 +35,7 @@ fun <P : PsiElement, A : Any> DiagnosticReporter.reportOn(
     source?.let { report(factory.on(it, a), context) }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 fun <P : PsiElement, A : Any, B : Any> DiagnosticReporter.reportOn(
     source: FirSourceElement?,
     factory: FirDiagnosticFactory2<P, A, B>,
@@ -43,6 +46,7 @@ fun <P : PsiElement, A : Any, B : Any> DiagnosticReporter.reportOn(
     source?.let { report(factory.on(it, a, b), context) }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 fun <P : PsiElement, A : Any, B : Any, C : Any> DiagnosticReporter.reportOn(
     source: FirSourceElement?,
     factory: FirDiagnosticFactory3<P, A, B, C>,
@@ -54,6 +58,7 @@ fun <P : PsiElement, A : Any, B : Any, C : Any> DiagnosticReporter.reportOn(
     source?.let { report(factory.on(it, a, b, c), context) }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 fun <P : PsiElement, A : Any, B : Any, C : Any, D : Any> DiagnosticReporter.reportOn(
     source: FirSourceElement?,
     factory: FirDiagnosticFactory4<P, A, B, C, D>,
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticFactory.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticFactory.kt
index 09bf47a9735..693522b3dab 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticFactory.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticFactory.kt
@@ -16,6 +16,9 @@ import org.jetbrains.kotlin.fir.FirLightSourceElement
 import org.jetbrains.kotlin.fir.FirPsiSourceElement
 import org.jetbrains.kotlin.fir.FirSourceElement
 
+@RequiresOptIn("Please use DiagnosticReporter.reportOn method if possible")
+annotation class InternalDiagnosticFactoryMethod
+
 sealed class AbstractFirDiagnosticFactory<D : FirDiagnostic<*>, P : PsiElement>(
     override val name: String,
     override val severity: Severity,
@@ -44,6 +47,7 @@ class FirDiagnosticFactory0<P : PsiElement>(
 ) : AbstractFirDiagnosticFactory<FirSimpleDiagnostic<*>, P>(name, severity, positioningStrategy) {
     override val firRenderer: FirDiagnosticRenderer<FirSimpleDiagnostic<*>> = SimpleFirDiagnosticRenderer("")
 
+    @InternalDiagnosticFactoryMethod
     fun on(element: FirSourceElement): FirSimpleDiagnostic<*> {
         return when (element) {
             is FirPsiSourceElement<*> -> FirPsiSimpleDiagnostic(
@@ -65,6 +69,7 @@ class FirDiagnosticFactory1<P : PsiElement, A>(
         FirDiagnosticRenderers.TO_STRING
     )
 
+    @InternalDiagnosticFactoryMethod
     fun on(element: FirSourceElement, a: A): FirDiagnosticWithParameters1<*, A> {
         return when (element) {
             is FirPsiSourceElement<*> -> FirPsiDiagnosticWithParameters1(
@@ -87,6 +92,7 @@ class FirDiagnosticFactory2<P : PsiElement, A, B>(
         FirDiagnosticRenderers.TO_STRING
     )
 
+    @InternalDiagnosticFactoryMethod
     fun on(element: FirSourceElement, a: A, b: B): FirDiagnosticWithParameters2<*, A, B> {
         return when (element) {
             is FirPsiSourceElement<*> -> FirPsiDiagnosticWithParameters2(
@@ -110,6 +116,7 @@ class FirDiagnosticFactory3<P : PsiElement, A, B, C>(
         FirDiagnosticRenderers.TO_STRING
     )
 
+    @InternalDiagnosticFactoryMethod
     fun on(element: FirSourceElement, a: A, b: B, c: C): FirDiagnosticWithParameters3<*, A, B, C> {
         return when (element) {
             is FirPsiSourceElement<*> -> FirPsiDiagnosticWithParameters3(
@@ -134,6 +141,7 @@ class FirDiagnosticFactory4<P : PsiElement, A, B, C, D>(
         FirDiagnosticRenderers.TO_STRING
     )
 
+    @InternalDiagnosticFactoryMethod
     fun on(element: FirSourceElement, a: A, b: B, c: C, d: D): FirDiagnosticWithParameters4<*, A, B, C, D> {
         return when (element) {
             is FirPsiSourceElement<*> -> FirPsiDiagnosticWithParameters4(
@@ -149,16 +157,19 @@ private fun incorrectElement(element: FirSourceElement): Nothing {
     throw IllegalArgumentException("Unknown element type: ${element::class}")
 }
 
+@InternalDiagnosticFactoryMethod
 fun <P : PsiElement> FirDiagnosticFactory0<P>.on(element: FirSourceElement?): FirSimpleDiagnostic<*>? {
     return element?.let { on(it) }
 }
 
+@InternalDiagnosticFactoryMethod
 fun <P : PsiElement, A> FirDiagnosticFactory1<P, A>.on(
     element: FirSourceElement?, a: A
 ): FirDiagnosticWithParameters1<*, A>? {
     return element?.let { on(it, a) }
 }
 
+@InternalDiagnosticFactoryMethod
 fun <P : PsiElement, A, B> FirDiagnosticFactory2<P, A, B>.on(
     element: FirSourceElement?,
     a: A,
@@ -167,6 +178,7 @@ fun <P : PsiElement, A, B> FirDiagnosticFactory2<P, A, B>.on(
     return element?.let { on(it, a, b) }
 }
 
+@InternalDiagnosticFactoryMethod
 fun <P : PsiElement, A, B, C> FirDiagnosticFactory3<P, A, B, C>.on(
     element: FirSourceElement?,
     a: A,
@@ -176,6 +188,7 @@ fun <P : PsiElement, A, B, C> FirDiagnosticFactory3<P, A, B, C>.on(
     return element?.let { on(it, a, b, c) }
 }
 
+@InternalDiagnosticFactoryMethod
 fun <P : PsiElement, A, B, C, D> FirDiagnosticFactory4<P, A, B, C, D>.on(
     element: FirSourceElement?,
     a: A,
@@ -184,4 +197,4 @@ fun <P : PsiElement, A, B, C, D> FirDiagnosticFactory4<P, A, B, C, D>.on(
     d: D
 ): FirDiagnosticWithParameters4<*, A, B, C, D>? {
     return element?.let { on(it, a, b, c, d) }
-}
\ No newline at end of file
+}
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt
index 6f50e18654d..b2fff2217db 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt
@@ -32,6 +32,7 @@ import org.jetbrains.kotlin.utils.addIfNotNull
 import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstance
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 private fun ConeDiagnostic.toFirDiagnostic(
     source: FirSourceElement,
     qualifiedAccessSource: FirSourceElement?
@@ -73,7 +74,7 @@ private fun ConeDiagnostic.toFirDiagnostic(
         FirErrors.NO_TYPE_ARGUMENTS_ON_RHS.on(qualifiedAccessSource ?: source, this.desiredCount, this.type)
     is ConeSimpleDiagnostic -> when (source.kind) {
         is FirFakeSourceElementKind -> null
-        else -> this.getFactory(source)?.on(qualifiedAccessSource ?: source)
+        else -> this.getFactory(source).on(qualifiedAccessSource ?: source)
     }
     is ConeInstanceAccessBeforeSuperCall -> FirErrors.INSTANCE_ACCESS_BEFORE_SUPER_CALL.on(source, this.target)
     is ConeStubDiagnostic -> null
@@ -97,6 +98,7 @@ fun ConeDiagnostic.toFirDiagnostics(
     }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 private fun mapUnsafeCallError(
     candidate: Candidate,
     rootCause: UnsafeCall,
@@ -146,6 +148,7 @@ private fun mapUnsafeCallError(
     }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 private fun mapInapplicableCandidateError(
     diagnostic: ConeInapplicableCandidateError,
     source: FirSourceElement,
@@ -200,7 +203,7 @@ private fun mapInapplicableCandidateError(
     }
 }
 
-@OptIn(ExperimentalStdlibApi::class)
+@OptIn(ExperimentalStdlibApi::class, InternalDiagnosticFactoryMethod::class)
 private fun mapSystemHasContradictionError(
     diagnostic: ConeConstraintSystemHasContradiction,
     source: FirSourceElement,
@@ -244,6 +247,7 @@ private fun mapSystemHasContradictionError(
     }
 }
 
+@OptIn(InternalDiagnosticFactoryMethod::class)
 private fun ConstraintSystemError.toDiagnostic(
     source: FirSourceElement,
     qualifiedAccessSource: FirSourceElement?,
@@ -327,7 +331,7 @@ private fun ConstraintSystemError.toDiagnostic(
 private val NewConstraintError.lowerConeType: ConeKotlinType get() = lowerType as ConeKotlinType
 private val NewConstraintError.upperConeType: ConeKotlinType get() = upperType as ConeKotlinType
 
-private fun ConeSimpleDiagnostic.getFactory(source: FirSourceElement): FirDiagnosticFactory0<*>? {
+private fun ConeSimpleDiagnostic.getFactory(source: FirSourceElement): FirDiagnosticFactory0<*> {
     @Suppress("UNCHECKED_CAST")
     return when (kind) {
         DiagnosticKind.Syntax -> FirErrors.SYNTAX
diff --git a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt
index f81957c75c6..46bf950fe93 100644
--- a/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt
+++ b/compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt
@@ -111,6 +111,7 @@ class FirDiagnosticsHandler(testServices: TestServices) : FirAnalysisHandler(tes
         return metaInfo
     }
 
+    @OptIn(InternalDiagnosticFactoryMethod::class)
     private fun collectSyntaxDiagnostics(
         testFile: TestFile,
         firFile: FirFile,