NI: Support forking inference with heuristics

Mostly, it only affects FIR

It partially allows to consider several variance of constraints like
A<Int> & A<T> <: A<X_var> that are mostly brought by smart casts

^KT-49542 Fixed
^KT-50489 Relates

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

@@ -13803,6 +13803,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/inference/selectOfLambdaWithExtensionEnabled.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastFork.kt")
+            public void testSmartCastFork() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastFork.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {
@@ -36583,6 +36589,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/testsWithStdLib/inference/kt4975.kt");
             }
 
+            @Test
+            @TestMetadata("plusAssignOnArrayList.kt")
+            public void testPlusAssignOnArrayList() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/inference/plusAssignOnArrayList.kt");
+            }
+
             @Test
             @TestMetadata("recursiveFlexibleAssertions.kt")
             public void testRecursiveFlexibleAssertions() throws Exception {

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

@@ -13803,6 +13803,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/inference/selectOfLambdaWithExtensionEnabled.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastFork.kt")
+            public void testSmartCastFork() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastFork.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {
@@ -36583,6 +36589,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/testsWithStdLib/inference/kt4975.kt");
             }
 
+            @Test
+            @TestMetadata("plusAssignOnArrayList.kt")
+            public void testPlusAssignOnArrayList() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/inference/plusAssignOnArrayList.kt");
+            }
+
             @Test
             @TestMetadata("recursiveFlexibleAssertions.kt")
             public void testRecursiveFlexibleAssertions() throws Exception {

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

@@ -503,6 +503,10 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         val ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION by deprecationError<KtExpression>(LanguageFeature.ProhibitAssigningSingleElementsToVarargsInNamedForm)
         val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION by warning<KtExpression>()
         val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION by warning<KtExpression>()
+
+        val INFERENCE_UNSUCCESSFUL_FORK by error<PsiElement> {
+            parameter<String>("message")
+        }
     }
 
     val AMBIGUITY by object : DiagnosticGroup("Ambiguity") {

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

@@ -341,6 +341,7 @@ object FirErrors {
     val ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION by deprecationError0<KtExpression>(ProhibitAssigningSingleElementsToVarargsInNamedForm)
     val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION by warning0<KtExpression>()
     val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION by warning0<KtExpression>()
+    val INFERENCE_UNSUCCESSFUL_FORK by error1<PsiElement, String>()
 
     // Ambiguity
     val OVERLOAD_RESOLUTION_AMBIGUITY by error1<PsiElement, Collection<FirBasedSymbol<*>>>(SourceElementPositioningStrategies.REFERENCE_BY_QUALIFIED)

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

@@ -250,6 +250,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INCONSISTENT_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INCORRECT_CHARACTER_LITERAL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INC_DEC_SHOULD_NOT_RETURN_UNIT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFERENCE_ERROR
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFERENCE_UNSUCCESSFUL_FORK
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFIX_MODIFIER_REQUIRED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INITIALIZATION_BEFORE_DECLARATION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION
@@ -928,6 +929,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
         )
         map.put(REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION, "Redundant spread (*) operator")
         map.put(REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION, "Redundant spread (*) operator")
+        map.put(INFERENCE_UNSUCCESSFUL_FORK, "Unsuccessful inference fork at position: {0}", TO_STRING)
 
         map.put(TYPE_MISMATCH, "Type mismatch: inferred type is {1} but {0} was expected", TO_STRING, TO_STRING, NOT_RENDERED)
         map.put(THROWABLE_TYPE_MISMATCH, "Throwable type mismatch: actual type is {0}", TO_STRING, NOT_RENDERED)

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

@@ -370,6 +370,12 @@ private fun ConstraintSystemError.toDiagnostic(
                 typeVariableName,
             )
         }
+        is NoSuccessfulFork -> {
+            FirErrors.INFERENCE_UNSUCCESSFUL_FORK.createOn(
+                source,
+                position.initialConstraint.asStringWithoutPosition(),
+            )
+        }
         else -> null
     }
 }

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

@@ -19,6 +19,7 @@ sealed class CallKind(vararg resolutionSequence: ResolutionStage) {
         CheckDslScopeViolation,
         CheckLowPriorityInOverloadResolution,
         PostponedVariablesInitializerResolutionStage,
+        ConstraintSystemForks
     )
 
     object SyntheticSelect : CallKind(
@@ -27,7 +28,8 @@ sealed class CallKind(vararg resolutionSequence: ResolutionStage) {
         CreateFreshTypeVariableSubstitutorStage,
         CollectTypeVariableUsagesInfo,
         CheckArguments,
-        EagerResolveOfCallableReferences
+        EagerResolveOfCallableReferences,
+        ConstraintSystemForks,
     )
 
     object Function : CallKind(
@@ -47,6 +49,7 @@ sealed class CallKind(vararg resolutionSequence: ResolutionStage) {
         EagerResolveOfCallableReferences,
         CheckLowPriorityInOverloadResolution,
         PostponedVariablesInitializerResolutionStage,
+        ConstraintSystemForks,
     )
 
     object DelegatingConstructorCall : CallKind(
@@ -62,6 +65,7 @@ sealed class CallKind(vararg resolutionSequence: ResolutionStage) {
         CheckDslScopeViolation,
         CheckArguments,
         EagerResolveOfCallableReferences,
+        ConstraintSystemForks,
     )
 
     object CallableReference : CallKind(
@@ -84,7 +88,8 @@ sealed class CallKind(vararg resolutionSequence: ResolutionStage) {
         CreateFreshTypeVariableSubstitutorStage,
         CollectTypeVariableUsagesInfo,
         CheckArguments,
-        EagerResolveOfCallableReferences
+        EagerResolveOfCallableReferences,
+        ConstraintSystemForks,
     )
 
     internal class CustomForIde(vararg resolutionSequence: ResolutionStage) : CallKind(*resolutionSequence)

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

@@ -7,14 +7,19 @@ package org.jetbrains.kotlin.fir.resolve.calls
 
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.Modality
-import org.jetbrains.kotlin.fir.*
+import org.jetbrains.kotlin.fir.FirVisibilityChecker
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.*
 import org.jetbrains.kotlin.fir.expressions.*
+import org.jetbrains.kotlin.fir.languageVersionSettings
+import org.jetbrains.kotlin.fir.matchingParameterFunctionType
 import org.jetbrains.kotlin.fir.references.FirSuperReference
 import org.jetbrains.kotlin.fir.resolve.directExpansionType
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
-import org.jetbrains.kotlin.fir.resolve.inference.*
+import org.jetbrains.kotlin.fir.resolve.inference.ConeTypeParameterBasedTypeVariable
+import org.jetbrains.kotlin.fir.resolve.inference.ResolvedCallableReferenceAtom
+import org.jetbrains.kotlin.fir.resolve.inference.csBuilder
+import org.jetbrains.kotlin.fir.resolve.inference.hasBuilderInferenceAnnotation
 import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.scopes.FirTypeScope
 import org.jetbrains.kotlin.fir.scopes.FirUnstableSmartcastTypeScope
@@ -25,6 +30,7 @@ import org.jetbrains.kotlin.fir.symbols.SyntheticSymbol
 import org.jetbrains.kotlin.fir.symbols.ensureResolved
 import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.fir.visibilityChecker
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -527,3 +533,15 @@ internal object CheckDeprecatedSinceKotlin : ResolutionStage() {
         }
     }
 }
+
+internal object ConstraintSystemForks : ResolutionStage() {
+    override suspend fun check(candidate: Candidate, callInfo: CallInfo, sink: CheckerSink, context: ResolutionContext) {
+        if (candidate.system.hasContradiction) return
+
+        candidate.system.processForkConstraints()
+
+        if (candidate.system.hasContradiction) {
+            sink.yieldDiagnostic(candidate.system.errors.firstOrNull()?.let(::InferenceError) ?: InapplicableCandidate)
+        }
+    }
+}

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConeConstraintSystemUtilContext.kt

@@ -125,4 +125,7 @@ object ConeConstraintSystemUtilContext : ConstraintSystemUtilContext {
 
     override val isForcedConsiderExtensionReceiverFromConstrainsInLambda: Boolean
         get() = true
+
+    override val isForcedAllowForkingInferenceSystem: Boolean
+        get() = true
 }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/ConstraintSystemCompleter.kt

@@ -50,6 +50,8 @@ class ConstraintSystemCompleter(private val components: BodyResolveComponents, p
     ) = with(c) {
         val topLevelTypeVariables = candidateReturnType.extractTypeVariables()
 
+        c.processForkConstraints()
+
         completion@ while (true) {
             val postponedArguments = getOrderedNotAnalyzedPostponedArguments(topLevelAtoms) // TODO: This is very slow