[FIR] Fix capturing of flexible types during resolution

Previously, because we didn't handle flexible types properly in
prepareCapturedType, projections inside flexible types would only be
captured during subtyping with captureStatus=FOR_SUBTYPING
which would lead to the constraint type being wrongly approximated
(see ConstraintInjector.TypeCheckerStateForConstraintInjector
.addNewIncorporatedConstraint).

Fixing the capturing produced two kinds of false positive diagnostics:

1. In ConstraintInjector.TypeCheckerStateForConstraintInjector
.addNewIncorporatedConstraint we would get two instances of cone types
that are structurally equal and containing the same captured type.
However, because we only skipped subtyping if the types were
referentially equal, we would get a contradiction here.
The fix was to use structural equality instead, which should be okay
as the captured type instances are the same.

2. Reified type variables were inferred to captured types because
flexible arrays with captured upper bounds
(Array<Foo>..Array<Captured(out Foo)>?) were not properly approximated.

#KT-62609 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -16424,6 +16424,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/inference/kt619.kt");
             }
 
+            @Test
+            @TestMetadata("kt62609.kt")
+            public void testKt62609() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/kt62609.kt");
+            }
+
             @Test
             @TestMetadata("lambdaArgumentWithLabel.kt")
             public void testLambdaArgumentWithLabel() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -16424,6 +16424,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/inference/kt619.kt");
             }
 
+            @Test
+            @TestMetadata("kt62609.kt")
+            public void testKt62609() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/kt62609.kt");
+            }
+
             @Test
             @TestMetadata("lambdaArgumentWithLabel.kt")
             public void testLambdaArgumentWithLabel() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -16418,6 +16418,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/inference/kt619.kt");
             }
 
+            @Test
+            @TestMetadata("kt62609.kt")
+            public void testKt62609() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/kt62609.kt");
+            }
+
             @Test
             @TestMetadata("lambdaArgumentWithLabel.kt")
             public void testLambdaArgumentWithLabel() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -16424,6 +16424,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/inference/kt619.kt");
             }
 
+            @Test
+            @TestMetadata("kt62609.kt")
+            public void testKt62609() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/kt62609.kt");
+            }
+
             @Test
             @TestMetadata("lambdaArgumentWithLabel.kt")
             public void testLambdaArgumentWithLabel() throws Exception {

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/ConeTypeContext.kt

@@ -412,6 +412,10 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext, Ty
         return this is ConeClassLikeLookupTag && classId == StandardClassIds.Nothing
     }
 
+    override fun TypeConstructorMarker.isArrayConstructor(): Boolean {
+        return this is ConeClassLikeLookupTag && classId == StandardClassIds.Array
+    }
+
     override fun SimpleTypeMarker.isSingleClassifierType(): Boolean {
         if (isError()) return false
         if (this is ConeCapturedType) return true

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/Arguments.kt

@@ -33,7 +33,6 @@ import org.jetbrains.kotlin.resolve.calls.inference.addSubtypeConstraintIfCompat
 import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.inference.model.SimpleConstraintSystemConstraintPosition
 import org.jetbrains.kotlin.types.AbstractTypeChecker
-import org.jetbrains.kotlin.types.model.CaptureStatus
 import org.jetbrains.kotlin.types.model.TypeSystemCommonSuperTypesContext
 import org.jetbrains.kotlin.types.model.typeConstructor
 
@@ -303,28 +302,9 @@ private fun argumentTypeWithCustomConversion(
     }
 }
 
-fun Candidate.prepareCapturedType(argumentType: ConeKotlinType, context: ResolutionContext): ConeKotlinType {
-    return captureTypeFromExpressionOrNull(argumentType, context) ?: argumentType
-}
-
-private fun Candidate.captureTypeFromExpressionOrNull(argumentType: ConeKotlinType, context: ResolutionContext): ConeKotlinType? {
-    val type = argumentType.fullyExpandedType(context.session)
-    if (type is ConeIntersectionType) {
-        val intersectedTypes = type.intersectedTypes.map { captureTypeFromExpressionOrNull(it, context) ?: it }
-        if (intersectedTypes == type.intersectedTypes) return null
-        return ConeIntersectionType(
-            intersectedTypes,
-            type.alternativeType?.let { captureTypeFromExpressionOrNull(it, context) ?: it }
-        )
-    }
-
-    if (type !is ConeClassLikeType && type !is ConeFlexibleType) return null
-
-    if (type.typeArguments.isEmpty()) return null
-
-    return context.session.typeContext.captureFromArgumentsInternal(
-        type, CaptureStatus.FROM_EXPRESSION
-    )
+internal fun prepareCapturedType(argumentType: ConeKotlinType, context: ResolutionContext): ConeKotlinType {
+    if (argumentType.isRaw()) return argumentType
+    return context.typeContext.captureFromExpression(argumentType.fullyExpandedType(context.session)) ?: argumentType
 }
 
 private fun checkApplicabilityForArgumentType(

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt

@@ -303,6 +303,9 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
     override fun TypeConstructorMarker.isNothingConstructor(): Boolean =
         this is IrClassSymbol && isClassWithFqName(StandardNames.FqNames.nothing)
 
+    override fun TypeConstructorMarker.isArrayConstructor(): Boolean =
+        this is IrClassSymbol && isClassWithFqName(StandardNames.FqNames.array)
+
     override fun SimpleTypeMarker.isSingleClassifierType() = true
 
     override fun SimpleTypeMarker.possibleIntegerTypes() = irBuiltIns.run {

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/inference/components/ConstraintInjector.kt

@@ -466,7 +466,12 @@ class ConstraintInjector(
             isFromNullabilityConstraint: Boolean,
             isFromDeclaredUpperBound: Boolean
         ) {
-            if (lowerType === upperType) return
+            // Avoid checking trivial incorporated constraints
+            if (isK2) {
+                if (lowerType == upperType) return
+            } else {
+                if (lowerType === upperType) return
+            }
             if (c.isAllowedType(lowerType) && c.isAllowedType(upperType)) {
                 fun runIsSubtypeOf() =
                     runIsSubtypeOf(lowerType, upperType, shouldTryUseDifferentFlexibilityForUpperType, isFromNullabilityConstraint)

compiler/resolution.common/src/org/jetbrains/kotlin/types/AbstractTypeApproximator.kt

@@ -143,10 +143,12 @@ abstract class AbstractTypeApproximator(
 
                     val lowerResult = approximateTo(lowerBound, conf, depth)
 
-                    val upperResult = if (!type.isRawType() && lowerBound.typeConstructor() == upperBound.typeConstructor())
+                    val upperResult = if (!type.isRawType() && !shouldApproximateUpperBoundSeparately(lowerBound, upperBound, conf)) {
+                        // We skip approximating the upper bound if the type constructors match as an optimization.
                         lowerResult?.withNullability(upperBound.isMarkedNullable())
-                    else
+                    } else {
                         approximateTo(upperBound, conf, depth)
+                    }
                     if (lowerResult == null && upperResult == null) return null
 
                     /**
@@ -168,11 +170,30 @@ abstract class AbstractTypeApproximator(
         }
     }
 
+    private fun shouldApproximateUpperBoundSeparately(
+        lowerBound: SimpleTypeMarker,
+        upperBound: SimpleTypeMarker,
+        conf: TypeApproximatorConfiguration,
+    ): Boolean {
+        val upperBoundConstructor = upperBound.typeConstructor()
+        if (lowerBound.typeConstructor() != upperBoundConstructor) return true
+
+        // Flexible arrays have the shape `Array<X>..Array<out X>?`.
+        // When such a type is captured, it results in `Array<X>..Array<Captured(out X)>?`, therefore it's necessary to approximate the
+        // upper bound separately.
+        // As an important performance optimization, we explicitly check if the type in question is an array with a captured type argument
+        // that needs to be approximated.
+        // This saves us from doing twice the work unnecessarily in many cases.
+        return isK2 &&
+                upperBoundConstructor.isArrayConstructor() &&
+                upperBound.getArgumentOrNull(0).let { it is CapturedTypeMarker && conf.capturedType(ctx, it) }
+    }
+
     private fun approximateLocalTypes(
         type: SimpleTypeMarker,
         conf: TypeApproximatorConfiguration,
         toSuper: Boolean,
-        depth: Int
+        depth: Int,
     ): SimpleTypeMarker? {
         if (!toSuper) return null
         if (!conf.localTypes && !conf.anonymous) return null

compiler/testData/diagnostics/tests/inference/commonSystem/nonFixedVariableFromBothBranches.fir.kt

@@ -12,8 +12,16 @@ fun <K> select(x: K, y: K): K = x
 
 fun <R> foo(f: () -> R): R = f()
 
+interface Inv<T> {
+    fun createArray(): Array<T>
+}
+
 fun test(n: Number) {
     val a = select(foo { JavaTest.createNumberArray() }, emptyArray())
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Array<kotlin.Number..kotlin.Number?!>..kotlin.Array<out kotlin.Number..kotlin.Number?!>?!")!>a<!>
+}
 
-    a
-}
+fun test2(inv: Inv<out CharSequence>) {
+    val a = select(foo { inv.createArray() }, emptyArray())
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Array<out kotlin.CharSequence>")!>a<!>
+}

compiler/testData/diagnostics/tests/inference/commonSystem/nonFixedVariableFromBothBranches.kt

@@ -12,8 +12,16 @@ fun <K> select(x: K, y: K): K = x
 
 fun <R> foo(f: () -> R): R = f()
 
+interface Inv<T> {
+    fun createArray(): Array<T>
+}
+
 fun test(n: Number) {
     val a = select(foo { JavaTest.createNumberArray() }, emptyArray())
-
     <!DEBUG_INFO_EXPRESSION_TYPE("(kotlin.Array<(kotlin.Number..kotlin.Number?)>..kotlin.Array<out (kotlin.Number..kotlin.Number?)>?)")!>a<!>
-}
+}
+
+fun test2(inv: Inv<out CharSequence>) {
+    val a = select(foo { inv.createArray() }, emptyArray())
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Array<out kotlin.CharSequence>")!>a<!>
+}

compiler/testData/diagnostics/tests/inference/commonSystem/nonFixedVariableFromBothBranches.txt

@@ -1,15 +0,0 @@
-package
-
-public fun </*0*/ R> foo(/*0*/ f: () -> R): R
-public fun </*0*/ K> select(/*0*/ x: K, /*1*/ y: K): K
-public fun test(/*0*/ n: kotlin.Number): kotlin.Unit
-
-public open class JavaTest {
-    public constructor JavaTest()
-    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
-
-    // Static members
-    public open fun createNumberArray(): kotlin.Array<(out) kotlin.Number!>!
-}

compiler/testData/diagnostics/tests/inference/kt62609.kt

@@ -0,0 +1,52 @@
+// FIR_IDENTICAL
+// ISSUE: KT-62609
+// FILE: I.java
+public interface I<T> {}
+
+// FILE: X.java
+public abstract class X<P> {}
+
+// FILE: A.java
+public final class A extends X<String> implements I<String> {
+    public static final A INSTANCE = new A();
+}
+
+// FILE: B.java
+public final class B extends X<Integer> implements I<Integer> {
+    public static final B INSTANCE = new B();
+}
+
+// FILE: test.kt
+fun test1() {
+    controlFun(A.INSTANCE)
+    controlFun(B.INSTANCE)
+    controlFun2(A.INSTANCE)
+    controlFun2(B.INSTANCE)
+
+    val a = when {
+        true -> A.INSTANCE
+        else -> B.INSTANCE
+    }
+
+    controlFun(a)
+    controlFun2(a)
+}
+
+fun test2() {
+    controlFun(A())
+    controlFun(B())
+    controlFun2(A())
+    controlFun2(B())
+
+    val a = when {
+        true -> A()
+        else -> B()
+    }
+
+    controlFun(a)
+    controlFun2(a)
+}
+
+
+fun <T> controlFun(c: I<T>) {}
+fun <T> controlFun2(c: X<T>) {}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -16424,6 +16424,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/inference/kt619.kt");
             }
 
+            @Test
+            @TestMetadata("kt62609.kt")
+            public void testKt62609() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/kt62609.kt");
+            }
+
             @Test
             @TestMetadata("lambdaArgumentWithLabel.kt")
             public void testLambdaArgumentWithLabel() throws Exception {

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -518,6 +518,7 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
 
     fun TypeConstructorMarker.isAnyConstructor(): Boolean
     fun TypeConstructorMarker.isNothingConstructor(): Boolean
+    fun TypeConstructorMarker.isArrayConstructor(): Boolean
 
     /**
      *

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -350,6 +350,11 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return KotlinBuiltIns.isTypeConstructorForGivenClass(this, FqNames.nothing)
     }
 
+    override fun TypeConstructorMarker.isArrayConstructor(): Boolean {
+        require(this is TypeConstructor, this::errorMessage)
+        return KotlinBuiltIns.isTypeConstructorForGivenClass(this, FqNames.array)
+    }
+
     override fun KotlinTypeMarker.asTypeArgument(): TypeArgumentMarker {
         require(this is KotlinType, this::errorMessage)
         return this.asTypeProjection()