FIR checker: report (expected|unnecessary) lateinit

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -344,6 +344,7 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
         val MUST_BE_INITIALIZED by error<FirSourceElement, KtProperty>(PositioningStrategy.DECLARATION_SIGNATURE)
         val MUST_BE_INITIALIZED_OR_BE_ABSTRACT by error<FirSourceElement, KtProperty>(PositioningStrategy.DECLARATION_SIGNATURE)
         val EXTENSION_PROPERTY_MUST_HAVE_ACCESSORS_OR_BE_ABSTRACT by error<FirSourceElement, KtProperty>(PositioningStrategy.DECLARATION_SIGNATURE)
+        val UNNECESSARY_LATEINIT by warning<FirSourceElement, KtProperty>(PositioningStrategy.LATEINIT_MODIFIER)
 
         val BACKING_FIELD_IN_INTERFACE by error<FirSourceElement, KtProperty>(PositioningStrategy.DECLARATION_SIGNATURE)
         val EXTENSION_PROPERTY_WITH_BACKING_FIELD by error<FirSourceElement, KtExpression>()
@@ -368,6 +369,7 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
 
         // TODO: need to cover `by` as well as delegate expression
         val EXPECTED_DELEGATED_PROPERTY by error<FirSourceElement, KtPropertyDelegate>()
+        val EXPECTED_LATEINIT_PROPERTY by error<FirSourceElement, KtModifierListOwner>(PositioningStrategy.LATEINIT_MODIFIER)
     }
 
     val DESTRUCTING_DECLARATION by object : DiagnosticGroup("Destructuring declaration") {

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -235,6 +235,7 @@ object FirErrors {
     val MUST_BE_INITIALIZED by error0<FirSourceElement, KtProperty>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val MUST_BE_INITIALIZED_OR_BE_ABSTRACT by error0<FirSourceElement, KtProperty>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val EXTENSION_PROPERTY_MUST_HAVE_ACCESSORS_OR_BE_ABSTRACT by error0<FirSourceElement, KtProperty>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
+    val UNNECESSARY_LATEINIT by warning0<FirSourceElement, KtProperty>(SourceElementPositioningStrategies.LATEINIT_MODIFIER)
     val BACKING_FIELD_IN_INTERFACE by error0<FirSourceElement, KtProperty>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val EXTENSION_PROPERTY_WITH_BACKING_FIELD by error0<FirSourceElement, KtExpression>()
     val PROPERTY_INITIALIZER_NO_BACKING_FIELD by error0<FirSourceElement, KtExpression>()
@@ -252,6 +253,7 @@ object FirErrors {
     val EXPECTED_DECLARATION_WITH_BODY by error0<FirSourceElement, KtDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val EXPECTED_PROPERTY_INITIALIZER by error0<FirSourceElement, KtExpression>()
     val EXPECTED_DELEGATED_PROPERTY by error0<FirSourceElement, KtPropertyDelegate>()
+    val EXPECTED_LATEINIT_PROPERTY by error0<FirSourceElement, KtModifierListOwner>(SourceElementPositioningStrategies.LATEINIT_MODIFIER)
 
     // Destructuring declaration
     val INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION by error0<FirSourceElement, KtDestructuringDeclaration>()

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

@@ -75,6 +75,7 @@ internal fun checkExpectDeclarationVisibilityAndBody(
     }
 }
 
+// Matched FE 1.0's [DeclarationsChecker#checkPropertyInitializer].
 internal fun checkPropertyInitializer(
     containingClass: FirRegularClass?,
     property: FirProperty,
@@ -136,20 +137,28 @@ internal fun checkPropertyInitializer(
             }
         }
         else -> {
+            val propertySource = property.source ?: return
             val isExternal = property.isEffectivelyExternal(containingClass, context)
             if (backingFieldRequired && !inInterface && !property.isLateInit && !isExpect && !isInitialized && !isExternal) {
-                property.source?.let {
+                if (property.receiverTypeRef != null && !property.hasAccessorImplementation) {
-                    if (property.receiverTypeRef != null && !property.hasAccessorImplementation) {
+                    reporter.reportOn(propertySource, FirErrors.EXTENSION_PROPERTY_MUST_HAVE_ACCESSORS_OR_BE_ABSTRACT, context)
-                        reporter.reportOn(it, FirErrors.EXTENSION_PROPERTY_MUST_HAVE_ACCESSORS_OR_BE_ABSTRACT, context)
+                } else { // TODO: can be suppressed not to report diagnostics about no body
-                    } else { // TODO: can be suppressed not to report diagnostics about no body
+                    if (containingClass == null || property.hasAccessorImplementation) {
-                        if (containingClass == null || property.hasAccessorImplementation) {
+                        reporter.reportOn(propertySource, FirErrors.MUST_BE_INITIALIZED, context)
-                            reporter.reportOn(it, FirErrors.MUST_BE_INITIALIZED, context)
+                    } else {
-                        } else {
+                        reporter.reportOn(propertySource, FirErrors.MUST_BE_INITIALIZED_OR_BE_ABSTRACT, context)
-                            reporter.reportOn(it, FirErrors.MUST_BE_INITIALIZED_OR_BE_ABSTRACT, context)
-                        }
                     }
                 }
             }
+            if (property.isLateInit) {
+                if (isExpect) {
+                    reporter.reportOn(propertySource, FirErrors.EXPECTED_LATEINIT_PROPERTY, context)
+                }
+                // TODO: like [BindingContext.MUST_BE_LATEINIT], we should consider variable with uninitialized error.
+                if (backingFieldRequired && !inInterface && isInitialized) {
+                    reporter.reportOn(propertySource, FirErrors.UNNECESSARY_LATEINIT, context)
+                }
+            }
         }
     }
 }
@@ -177,4 +186,4 @@ internal fun FirRegularClass.isInlineOrValueClass(): Boolean {
 
     val modifierList = with(FirModifierList) { source.getModifierList() }
     return isInline || modifierList?.modifiers?.any { it.token == KtTokens.VALUE_KEYWORD } == true
-}
+}

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

@@ -148,7 +148,14 @@ object FirMemberPropertiesChecker : FirRegularClassChecker() {
         // So, our source of truth should be the full modifier list retrieved from the source.
         val modifierList = with(FirModifierList) { property.source.getModifierList() }
 
-        checkPropertyInitializer(containingDeclaration, property, modifierList, isInitialized, reporter, context)
+        checkPropertyInitializer(
+            containingDeclaration,
+            property,
+            modifierList,
+            isInitialized,
+            reporter,
+            context
+        )
         checkPropertyAccessors(property, reporter, context)
         checkExpectDeclarationVisibilityAndBody(property, source, reporter, context)
 

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

@@ -28,7 +28,14 @@ object FirTopLevelPropertiesChecker : FirFileChecker() {
         // So, our source of truth should be the full modifier list retrieved from the source.
         val modifierList = with(FirModifierList) { source.getModifierList() }
 
-        checkPropertyInitializer(null, property, modifierList, property.initializer != null, reporter, context)
+        checkPropertyInitializer(
+            containingClass = null,
+            property,
+            modifierList,
+            isInitialized = property.initializer != null,
+            reporter,
+            context
+        )
         checkPropertyAccessors(property, reporter, context)
         checkExpectDeclarationVisibilityAndBody(property, source, reporter, context)
     }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -66,6 +66,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ERROR_FROM_JAVA_R
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ERROR_IN_CONTRACT_DESCRIPTION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_DECLARATION_WITH_BODY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_DELEGATED_PROPERTY
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_LATEINIT_PROPERTY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_PRIVATE_DECLARATION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_PROPERTY_INITIALIZER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPLICIT_DELEGATION_CALL_REQUIRED
@@ -181,6 +182,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETERS_I
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_AS_SUPERTYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.TYPE_PARAMETER_IN_CATCH_CLAUSE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNINITIALIZED_VARIABLE
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNNECESSARY_LATEINIT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNRESOLVED_LABEL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNRESOLVED_REFERENCE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.UNSAFE_CALL
@@ -515,6 +517,7 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(MUST_BE_INITIALIZED, "Property must be initialized")
             map.put(MUST_BE_INITIALIZED_OR_BE_ABSTRACT, "Property must be initialized or be abstract")
             map.put(EXTENSION_PROPERTY_MUST_HAVE_ACCESSORS_OR_BE_ABSTRACT, "Extension property must have accessors or be abstract")
+            map.put(UNNECESSARY_LATEINIT, "Lateinit is unnecessary: definitely initialized in constructors")
 
             map.put(BACKING_FIELD_IN_INTERFACE, "Property in an interface cannot have a backing field")
             map.put(EXTENSION_PROPERTY_WITH_BACKING_FIELD, "Extension property cannot be initialized because it has no backing field")
@@ -534,6 +537,7 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(EXPECTED_PROPERTY_INITIALIZER, "Expected property cannot have an initializer")
             map.put(EXPECTED_DELEGATED_PROPERTY, "Expected property cannot be delegated")
             map.put(EXPECTED_PRIVATE_DECLARATION, "Expected declaration cannot be private")
+            map.put(EXPECTED_LATEINIT_PROPERTY, "Expected property cannot be lateinit")
 
             // Destructuring declaration
             map.put(INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION, "Initializer required for destructuring declaration")

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitRecursiveInLambda.fir.kt

@@ -0,0 +1,6 @@
+class Test {
+    <!UNNECESSARY_LATEINIT!>lateinit<!> var someRunnable: Runnable
+    init {
+        someRunnable = Runnable { someRunnable.run() }
+    }
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitRecursiveInLambda.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 class Test {
     lateinit var someRunnable: Runnable
     init {

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithConstructor.fir.kt

@@ -1,9 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-class Foo {
-    lateinit var bar: String
-
-    constructor(baz: Int) {
-        bar = ""
-    }
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithConstructor.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class Foo {

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithInit.fir.kt

@@ -1,7 +0,0 @@
-class Foo {
-    lateinit var bar: String
-
-    init {
-        bar = ""
-    }
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithInit.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 class Foo {
     <!UNNECESSARY_LATEINIT!>lateinit<!> var bar: String
 

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithMultipleConstructors.fir.kt

@@ -1,13 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-class Foo {
-    lateinit var bar: String
-
-    constructor() {
-        bar = ""
-    }
-
-    constructor(baz: Int) {
-        bar = ""
-    }
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithMultipleConstructors.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class Foo {

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithMultipleConstructorsAndDelegation.fir.kt

@@ -1,15 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-class Foo {
-    lateinit var bar: String
-
-    constructor() {
-        bar = ""
-    }
-
-    constructor(a: Int) : this() {
-    }
-
-    constructor(a: Int, b: Int) : this(a) {
-    }
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithMultipleConstructorsAndDelegation.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class Foo {

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithPlusAssign.fir.kt

@@ -0,0 +1,8 @@
+class Foo {
+    <!UNNECESSARY_LATEINIT!>lateinit<!> var bar: String
+
+    constructor(baz: Int) {
+        // At best, we should have error here despite of lateinit
+        bar += baz
+    }
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/lateinitWithPlusAssign.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 class Foo {
     lateinit var bar: String
 

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/secondaryConstructorDelegateItself.fir.kt

@@ -1,13 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-class Foo {
-    lateinit var bar: String
-
-    constructor() {
-        bar = ""
-    }
-
-    constructor(a: Int) : <!CYCLIC_CONSTRUCTOR_DELEGATION_CALL!>this<!>(a) {
-        bar = "a"
-    }
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unnecessaryLateinit/secondaryConstructorDelegateItself.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class Foo {

compiler/testData/diagnostics/tests/multiplatform/headerClass/memberPropertyKinds.fir.kt

@@ -23,7 +23,7 @@ expect class Foo {
     get() = "no"
     set(value) {}
 
-    lateinit var lateinitVar: String
+    <!EXPECTED_LATEINIT_PROPERTY!>lateinit<!> var lateinitVar: String
 
     val delegated: String by <!EXPECTED_DELEGATED_PROPERTY!>Delegate<!>
 }

compiler/testData/diagnostics/tests/multiplatform/topLevelProperty/differentKindsOfProperties.fir.kt

@@ -28,7 +28,7 @@ expect var customAccessorVar: String
 
 expect const val constVal: Int
 
-expect lateinit var lateinitVar: String
+expect <!EXPECTED_LATEINIT_PROPERTY!>lateinit<!> var lateinitVar: String
 
 expect val delegated: String by <!EXPECTED_DELEGATED_PROPERTY!>Delegate<!>
 object Delegate { operator fun getValue(x: Any?, y: Any?): String = "" }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -1021,6 +1021,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.UNNECESSARY_LATEINIT) { firDiagnostic ->
+        UnnecessaryLateinitImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.BACKING_FIELD_IN_INTERFACE) { firDiagnostic ->
         BackingFieldInInterfaceImpl(
             firDiagnostic as FirPsiDiagnostic<*>,
@@ -1111,6 +1117,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.EXPECTED_LATEINIT_PROPERTY) { firDiagnostic ->
+        ExpectedLateinitPropertyImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION) { firDiagnostic ->
         InitializerRequiredForDestructuringDeclarationImpl(
             firDiagnostic as FirPsiDiagnostic<*>,

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -719,6 +719,10 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = ExtensionPropertyMustHaveAccessorsOrBeAbstract::class
     }
 
+    abstract class UnnecessaryLateinit : KtFirDiagnostic<KtProperty>() {
+        override val diagnosticClass get() = UnnecessaryLateinit::class
+    }
+
     abstract class BackingFieldInInterface : KtFirDiagnostic<KtProperty>() {
         override val diagnosticClass get() = BackingFieldInInterface::class
     }
@@ -779,6 +783,10 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = ExpectedDelegatedProperty::class
     }
 
+    abstract class ExpectedLateinitProperty : KtFirDiagnostic<KtModifierListOwner>() {
+        override val diagnosticClass get() = ExpectedLateinitProperty::class
+    }
+
     abstract class InitializerRequiredForDestructuringDeclaration : KtFirDiagnostic<KtDestructuringDeclaration>() {
         override val diagnosticClass get() = InitializerRequiredForDestructuringDeclaration::class
     }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -1164,6 +1164,13 @@ internal class ExtensionPropertyMustHaveAccessorsOrBeAbstractImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class UnnecessaryLateinitImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.UnnecessaryLateinit(), KtAbstractFirDiagnostic<KtProperty> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class BackingFieldInInterfaceImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
@@ -1269,6 +1276,13 @@ internal class ExpectedDelegatedPropertyImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class ExpectedLateinitPropertyImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.ExpectedLateinitProperty(), KtAbstractFirDiagnostic<KtModifierListOwner> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class InitializerRequiredForDestructuringDeclarationImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,