diff --git a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/lazy/resolve/NonLocalDeclarationUtils.kt b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/lazy/resolve/NonLocalDeclarationUtils.kt
index 8abb69fae71..c29c19eb8b7 100644
--- a/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/lazy/resolve/NonLocalDeclarationUtils.kt
+++ b/analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/lazy/resolve/NonLocalDeclarationUtils.kt
@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.KtFakeSourceElement
 import org.jetbrains.kotlin.KtFakeSourceElementKind
 import org.jetbrains.kotlin.analysis.api.impl.barebone.parentOfType
 import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.fir.psi
 import org.jetbrains.kotlin.psi
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.containingClassOrObject
diff --git a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/model/RegularDiagnosticData.kt b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/model/RegularDiagnosticData.kt
index 711996b688e..2b14b83b2d8 100644
--- a/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/model/RegularDiagnosticData.kt
+++ b/compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/model/RegularDiagnosticData.kt
@@ -117,7 +117,7 @@ enum class PositioningStrategy(private val strategy: String? = null) {
     val expressionToCreate get() = "SourceElementPositioningStrategies.${strategy ?: name}"
 
     companion object {
-        const val importToAdd = "org.jetbrains.kotlin.fir.analysis.diagnostics.SourceElementPositioningStrategies"
+        const val importToAdd = "org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies"
     }
 }
 
diff --git a/compiler/fir/checkers/checkers.jvm/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/jvm/FirJvmErrors.kt b/compiler/fir/checkers/checkers.jvm/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/jvm/FirJvmErrors.kt
index b38d3123e5c..5d640ba261b 100644
--- a/compiler/fir/checkers/checkers.jvm/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/jvm/FirJvmErrors.kt
+++ b/compiler/fir/checkers/checkers.jvm/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/jvm/FirJvmErrors.kt
@@ -12,8 +12,8 @@ import org.jetbrains.kotlin.config.LanguageFeature.ProhibitJvmOverloadsOnConstru
 import org.jetbrains.kotlin.config.LanguageFeature.ProhibitSpreadOnSignaturePolymorphicCall
 import org.jetbrains.kotlin.config.LanguageFeature.RepeatableAnnotationContainerConstraints
 import org.jetbrains.kotlin.diagnostics.*
+import org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.fir.analysis.diagnostics.*
-import org.jetbrains.kotlin.fir.analysis.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.name.ClassId
diff --git a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
index c2a5a7faf52..14918233c93 100644
--- a/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
+++ b/compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt
@@ -23,9 +23,9 @@ import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.EffectiveVisibility
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.diagnostics.*
+import org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.diagnostics.WhenMissingCase
 import org.jetbrains.kotlin.fir.FirModuleData
-import org.jetbrains.kotlin.fir.analysis.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
 import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
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 4ff9679a7e6..0a6df9cb8b2 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
@@ -13,6 +13,9 @@ import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.annotations.KotlinTarget
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.modalityModifier
+import org.jetbrains.kotlin.diagnostics.overrideModifier
+import org.jetbrains.kotlin.diagnostics.visibilityModifier
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.diagnostics.*
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirKeywordUtils.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirKeywordUtils.kt
index fe4e7bd54c2..f6a0f86803d 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirKeywordUtils.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirKeywordUtils.kt
@@ -11,7 +11,7 @@ import com.intellij.psi.tree.TokenSet
 import com.intellij.util.diff.FlyweightCapableTreeStructure
 import org.jetbrains.kotlin.*
 import org.jetbrains.kotlin.fir.FirElement
-import org.jetbrains.kotlin.fir.analysis.diagnostics.valOrVarKeyword
+import org.jetbrains.kotlin.diagnostics.valOrVarKeyword
 import org.jetbrains.kotlin.lexer.KtKeywordToken
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.lexer.KtTokens
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/SourceNavigator.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/SourceNavigator.kt
index 93a77aa6f5e..8f3bff96457 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/SourceNavigator.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/SourceNavigator.kt
@@ -14,8 +14,8 @@ import org.jetbrains.kotlin.KtPsiSourceElement
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.fir.FirElement
-import org.jetbrains.kotlin.fir.analysis.diagnostics.getAncestors
-import org.jetbrains.kotlin.fir.analysis.diagnostics.nameIdentifier
+import org.jetbrains.kotlin.diagnostics.getAncestors
+import org.jetbrains.kotlin.diagnostics.nameIdentifier
 import org.jetbrains.kotlin.fir.declarations.FirDeclaration
 import org.jetbrains.kotlin.fir.symbols.impl.FirValueParameterSymbol
 import org.jetbrains.kotlin.fir.types.FirTypeRef
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationChecker.kt
index 8d519866da2..0797e6869e0 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationChecker.kt
@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.annotations.AnnotationUseSiteTarget
 import org.jetbrains.kotlin.descriptors.annotations.KotlinTarget
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.hasValOrVar
 import org.jetbrains.kotlin.fir.FirAnnotationContainer
 import org.jetbrains.kotlin.fir.analysis.checkers.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationClassDeclarationChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationClassDeclarationChecker.kt
index 6db3f18299f..0b487f23e6b 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationClassDeclarationChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirAnnotationClassDeclarationChecker.kt
@@ -11,6 +11,8 @@ import org.jetbrains.kotlin.descriptors.ClassKind.ANNOTATION_CLASS
 import org.jetbrains.kotlin.descriptors.ClassKind.ENUM_CLASS
 import org.jetbrains.kotlin.descriptors.annotations.KotlinTarget
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.hasValOrVar
+import org.jetbrains.kotlin.diagnostics.hasVar
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.analysis.checkers.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConstructorInInterfaceChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConstructorInInterfaceChecker.kt
index 74b3b93a1bf..7104a47cfb5 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConstructorInInterfaceChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConstructorInInterfaceChecker.kt
@@ -8,7 +8,7 @@ package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
-import org.jetbrains.kotlin.fir.analysis.diagnostics.hasPrimaryConstructor
+import org.jetbrains.kotlin.diagnostics.hasPrimaryConstructor
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.FirRegularClass
 import org.jetbrains.kotlin.fir.declarations.utils.isInterface
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantModalityModifierSyntaxChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantModalityModifierSyntaxChecker.kt
index a442ca76f07..524bcd578ed 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantModalityModifierSyntaxChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantModalityModifierSyntaxChecker.kt
@@ -14,7 +14,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.implicitModality
 import org.jetbrains.kotlin.fir.analysis.checkers.syntax.FirDeclarationSyntaxChecker
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.REDUNDANT_MODALITY_MODIFIER
-import org.jetbrains.kotlin.fir.analysis.diagnostics.modalityModifier
+import org.jetbrains.kotlin.diagnostics.modalityModifier
 import org.jetbrains.kotlin.fir.analysis.diagnostics.reportOn
 import org.jetbrains.kotlin.fir.declarations.FirClass
 import org.jetbrains.kotlin.fir.declarations.FirDeclaration
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantVisibilityModifierSyntaxChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantVisibilityModifierSyntaxChecker.kt
index ee3f54f2ef0..3770c8ea9b9 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantVisibilityModifierSyntaxChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/RedundantVisibilityModifierSyntaxChecker.kt
@@ -11,6 +11,8 @@ import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.overrideModifier
+import org.jetbrains.kotlin.diagnostics.visibilityModifier
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.context.findClosest
 import org.jetbrains.kotlin.fir.analysis.checkers.findClosestClassOrObject
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirAnonymousFunctionSyntaxChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirAnonymousFunctionSyntaxChecker.kt
index ddbcce2cbcc..066b619a76c 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirAnonymousFunctionSyntaxChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirAnonymousFunctionSyntaxChecker.kt
@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.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.diagnostics.typeParametersList
 import org.jetbrains.kotlin.fir.declarations.FirAnonymousFunction
 import org.jetbrains.kotlin.psi.KtFunction
 
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirFunctionTypeParametersSyntaxChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirFunctionTypeParametersSyntaxChecker.kt
index ef807325389..1e4f8f82dcc 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirFunctionTypeParametersSyntaxChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirFunctionTypeParametersSyntaxChecker.kt
@@ -10,6 +10,8 @@ import org.jetbrains.kotlin.KtLightSourceElement
 import org.jetbrains.kotlin.KtPsiSourceElement
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.nameIdentifier
+import org.jetbrains.kotlin.diagnostics.typeParametersList
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.diagnostics.*
 import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirLocalVariableTypeParametersSyntaxChecker.kt b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirLocalVariableTypeParametersSyntaxChecker.kt
index 1e6ff5853e2..04fcd5484cc 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirLocalVariableTypeParametersSyntaxChecker.kt
+++ b/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/syntax/FirLocalVariableTypeParametersSyntaxChecker.kt
@@ -14,7 +14,7 @@ import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.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.diagnostics.typeParametersList
 import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.psi.KtProperty
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategies.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategies.kt
similarity index 98%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategies.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategies.kt
index d22e0bcb7e5..4f715712c91 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategies.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategies.kt
@@ -1,9 +1,9 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
+package org.jetbrains.kotlin.diagnostics
 
 import com.intellij.lang.LighterASTNode
 import com.intellij.openapi.util.Ref
@@ -14,8 +14,6 @@ import com.intellij.util.diff.FlyweightCapableTreeStructure
 import org.jetbrains.kotlin.KtNodeType
 import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.KtSourceElement
-import org.jetbrains.kotlin.diagnostics.KtDiagnostic
-import org.jetbrains.kotlin.diagnostics.KtDiagnosticWithParameters2
 import org.jetbrains.kotlin.diagnostics.PositioningStrategies
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.lexer.KtTokens.MODALITY_MODIFIERS
@@ -1099,7 +1097,7 @@ private fun FlyweightCapableTreeStructure<LighterASTNode>.fieldKeyword(node: Lig
 private fun FlyweightCapableTreeStructure<LighterASTNode>.byKeyword(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, KtTokens.BY_KEYWORD)
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.nameIdentifier(node: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.nameIdentifier(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, KtTokens.IDENTIFIER)
 
 private fun FlyweightCapableTreeStructure<LighterASTNode>.operationReference(node: LighterASTNode): LighterASTNode? =
@@ -1176,22 +1174,22 @@ private fun FlyweightCapableTreeStructure<LighterASTNode>.rightParenthesis(node:
 private fun FlyweightCapableTreeStructure<LighterASTNode>.objectKeyword(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, KtTokens.OBJECT_KEYWORD)
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.valOrVarKeyword(node: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.valOrVarKeyword(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, VAL_VAR_TOKEN_SET)
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.visibilityModifier(declaration: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.visibilityModifier(declaration: LighterASTNode): LighterASTNode? =
     modifierList(declaration)?.let { findChildByType(it, VISIBILITY_MODIFIERS) }
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.modalityModifier(declaration: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.modalityModifier(declaration: LighterASTNode): LighterASTNode? =
     modifierList(declaration)?.let { findChildByType(it, MODALITY_MODIFIERS) }
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.overrideModifier(declaration: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.overrideModifier(declaration: LighterASTNode): LighterASTNode? =
     modifierList(declaration)?.let { findChildByType(it, KtTokens.OVERRIDE_KEYWORD) }
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.inlineModifier(declaration: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.inlineModifier(declaration: LighterASTNode): LighterASTNode? =
     modifierList(declaration)?.let { findChildByType(it, KtTokens.INLINE_KEYWORD) }
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.typeParametersList(declaration: LighterASTNode): LighterASTNode? =
+fun FlyweightCapableTreeStructure<LighterASTNode>.typeParametersList(declaration: LighterASTNode): LighterASTNode? =
     findChildByType(declaration, KtNodeTypes.TYPE_PARAMETER_LIST)
 
 private fun FlyweightCapableTreeStructure<LighterASTNode>.supertypesList(node: LighterASTNode): LighterASTNode? =
@@ -1379,7 +1377,7 @@ private fun FlyweightCapableTreeStructure<LighterASTNode>.findParentOfType(
     return null
 }
 
-internal fun FlyweightCapableTreeStructure<LighterASTNode>.getAncestors(node: LighterASTNode): Sequence<LighterASTNode> =
+fun FlyweightCapableTreeStructure<LighterASTNode>.getAncestors(node: LighterASTNode): Sequence<LighterASTNode> =
     generateSequence(getParent(node)) { getParent(it) }
 
 private fun FlyweightCapableTreeStructure<LighterASTNode>.firstChild(node: LighterASTNode): LighterASTNode? {
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategy.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategy.kt
similarity index 91%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategy.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategy.kt
index 3538deaaccb..abdc4c1f21f 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/LightTreePositioningStrategy.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategy.kt
@@ -1,9 +1,9 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
+package org.jetbrains.kotlin.diagnostics
 
 import com.intellij.lang.LighterASTNode
 import com.intellij.openapi.util.Ref
@@ -11,8 +11,6 @@ import com.intellij.openapi.util.TextRange
 import com.intellij.psi.TokenType
 import com.intellij.util.diff.FlyweightCapableTreeStructure
 import org.jetbrains.kotlin.KtSourceElement
-import org.jetbrains.kotlin.diagnostics.KtDiagnostic
-import org.jetbrains.kotlin.fir.analysis.checkers.getChildren
 import org.jetbrains.kotlin.lexer.KtSingleValueToken
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.lexer.KtTokens.WHITE_SPACE
@@ -84,10 +82,10 @@ private val FILLER_TOKENS = setOf(
 )
 
 private fun LighterASTNode.nonFillerFirstChildOrSelf(tree: FlyweightCapableTreeStructure<LighterASTNode>): LighterASTNode =
-    getChildren(tree).firstOrNull { !it.isFiller() } ?: this
+    getChildren(tree).firstOrNull { !(it?.isFiller() ?: false) } ?: this
 
 internal fun LighterASTNode.nonFillerLastChildOrSelf(tree: FlyweightCapableTreeStructure<LighterASTNode>): LighterASTNode =
-    getChildren(tree).lastOrNull { !it.isFiller() } ?: this
+    getChildren(tree).lastOrNull { !(it?.isFiller() ?: false) } ?: this
 
 internal fun LighterASTNode.isFiller() = tokenType in FILLER_TOKENS
 
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/PsiPositioningStrategies.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/PsiPositioningStrategies.kt
similarity index 86%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/PsiPositioningStrategies.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/PsiPositioningStrategies.kt
index 9bf17fbc281..0ae6a2e1259 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/PsiPositioningStrategies.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/PsiPositioningStrategies.kt
@@ -3,17 +3,13 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
+package org.jetbrains.kotlin.diagnostics
 
 import com.intellij.openapi.util.TextRange
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.KtPsiSourceElement
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.cfg.UnreachableCode
-import org.jetbrains.kotlin.diagnostics.DiagnosticMarker
-import org.jetbrains.kotlin.diagnostics.KtDiagnostic
-import org.jetbrains.kotlin.diagnostics.KtDiagnosticWithParameters2
-import org.jetbrains.kotlin.diagnostics.PositioningStrategy
 import org.jetbrains.kotlin.psi
 import org.jetbrains.kotlin.psi.KtElement
 import org.jetbrains.kotlin.psi.KtNamedDeclaration
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategies.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategies.kt
similarity index 97%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategies.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategies.kt
index e40639645e5..9047737eede 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategies.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategies.kt
@@ -1,12 +1,9 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
-
-import org.jetbrains.kotlin.diagnostics.AbstractSourceElementPositioningStrategy
-import org.jetbrains.kotlin.diagnostics.PositioningStrategies
+package org.jetbrains.kotlin.diagnostics
 
 object SourceElementPositioningStrategies {
     val DEFAULT = SourceElementPositioningStrategy(
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategy.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategy.kt
similarity index 93%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategy.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategy.kt
index 13f3967077c..edc1b65de99 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/SourceElementPositioningStrategy.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/SourceElementPositioningStrategy.kt
@@ -3,7 +3,7 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
+package org.jetbrains.kotlin.diagnostics
 
 import com.intellij.openapi.util.TextRange
 import com.intellij.psi.PsiElement
@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.KtPsiSourceElement
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.diagnostics.AbstractSourceElementPositioningStrategy
 import org.jetbrains.kotlin.diagnostics.KtDiagnostic
+import org.jetbrains.kotlin.diagnostics.LightTreePositioningStrategy
 import org.jetbrains.kotlin.diagnostics.PositioningStrategy
 
 class SourceElementPositioningStrategy(
diff --git a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/UnreachableCodeLightTreeHelper.kt b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/UnreachableCodeLightTreeHelper.kt
similarity index 88%
rename from compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/UnreachableCodeLightTreeHelper.kt
rename to compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/UnreachableCodeLightTreeHelper.kt
index 01e1d0526e9..946897926a6 100644
--- a/compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/UnreachableCodeLightTreeHelper.kt
+++ b/compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/UnreachableCodeLightTreeHelper.kt
@@ -3,12 +3,12 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.fir.analysis.diagnostics
+package org.jetbrains.kotlin.diagnostics
 
 import com.intellij.lang.LighterASTNode
+import com.intellij.openapi.util.Ref
 import com.intellij.openapi.util.TextRange
 import com.intellij.util.diff.FlyweightCapableTreeStructure
-import org.jetbrains.kotlin.fir.analysis.checkers.getChildren
 import org.jetbrains.kotlin.lexer.KtTokens
 
 typealias Node = LighterASTNode
@@ -83,4 +83,10 @@ class UnreachableCodeLightTreeHelper(val tree: FlyweightCapableTreeStructure<Nod
         }
         return result
     }
-}
\ No newline at end of file
+}
+
+internal fun LighterASTNode.getChildren(tree: FlyweightCapableTreeStructure<LighterASTNode>): List<LighterASTNode?> {
+    val children = Ref<Array<LighterASTNode?>>()
+    val count = tree.getChildren(this, children)
+    return if (count > 0) children.get().filterNotNull() else emptyList()
+}