FIR: Avoid reporting redundant TYPE_MISMATCH (for assignments)

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

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.fir.diagnostics.*
 import org.jetbrains.kotlin.fir.resolve.calls.*
 import org.jetbrains.kotlin.fir.resolve.diagnostics.*
 import org.jetbrains.kotlin.fir.resolve.inference.model.ConeArgumentConstraintPosition
+import org.jetbrains.kotlin.fir.resolve.inference.model.ConeExpectedTypeConstraintPosition
 import org.jetbrains.kotlin.fir.resolve.inference.model.ConeExplicitTypeParameterConstraintPosition
 import org.jetbrains.kotlin.fir.resolve.inference.model.ConeLambdaArgumentConstraintPosition
 import org.jetbrains.kotlin.fir.symbols.impl.FirBackingFieldSymbol
@@ -164,19 +165,36 @@ private fun mapSystemHasContradictionError(
     source: FirSourceElement,
     qualifiedAccessSource: FirSourceElement?,
 ): List<FirDiagnostic<FirSourceElement>> {
+    val errorsToIgnore = mutableSetOf<ConstraintSystemError>()
     return buildList<FirDiagnostic<FirSourceElement>> {
         for (error in diagnostic.candidate.system.errors) {
-            addIfNotNull(error.toDiagnostic(source, qualifiedAccessSource, diagnostic.candidate.callInfo.session.typeContext))
+            addIfNotNull(
+                error.toDiagnostic(
+                    source,
+                    qualifiedAccessSource,
+                    diagnostic.candidate.callInfo.session.typeContext,
+                    errorsToIgnore,
+                )
+            )
         }
     }.ifEmpty {
         listOfNotNull(
             diagnostic.candidate.system.errors.firstNotNullOfOrNull {
+                if (it in errorsToIgnore) return@firstNotNullOfOrNull null
                 val message = when (it) {
                     is NewConstraintError -> "NewConstraintError at ${it.position}: ${it.lowerType} <!: ${it.upperType}"
                     // Error should be reported on the error type itself
                     is ConstrainingTypeIsError -> return@firstNotNullOfOrNull null
                     else -> "Inference error: ${it::class.simpleName}"
                 }
+
+                if (it is NewConstraintError && it.position.from is FixVariableConstraintPosition<*>) {
+                    val morePreciseDiagnosticExists = diagnostic.candidate.system.errors.any { other ->
+                        other is NewConstraintError && other.position.from !is FixVariableConstraintPosition<*>
+                    }
+                    if (morePreciseDiagnosticExists) return@firstNotNullOfOrNull null
+                }
+
                 FirErrors.NEW_INFERENCE_ERROR.on(qualifiedAccessSource ?: source, message)
             }
         )
@@ -187,6 +205,7 @@ private fun ConstraintSystemError.toDiagnostic(
     source: FirSourceElement,
     qualifiedAccessSource: FirSourceElement?,
     typeContext: ConeTypeContext,
+    errorsToIgnore: MutableSet<ConstraintSystemError>,
 ): FirDiagnostic<FirSourceElement>? {
     return when (this) {
         is NewConstraintError -> {
@@ -204,7 +223,11 @@ private fun ConstraintSystemError.toDiagnostic(
             }
 
             when (position) {
-                is ExpectedTypeConstraintPosition<*> -> {
+                is ConeExpectedTypeConstraintPosition -> {
+                    if (position.expectedTypeMismatchIsReportedInChecker) {
+                        errorsToIgnore.add(this)
+                        return null
+                    }
                     val inferredType =
                         if (!lowerConeType.isNullableNothing)
                             lowerConeType

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/ResolutionMode.kt

@@ -15,8 +15,13 @@ sealed class ResolutionMode {
     object ContextDependent : ResolutionMode()
     object ContextDependentDelegate : ResolutionMode()
     object ContextIndependent : ResolutionMode()
+
     // TODO: it's better not to use WithExpectedType(FirImplicitTypeRef)
-    class WithExpectedType(val expectedTypeRef: FirTypeRef, val mayBeCoercionToUnitApplied: Boolean = false) : ResolutionMode()
+    class WithExpectedType(
+        val expectedTypeRef: FirTypeRef,
+        val mayBeCoercionToUnitApplied: Boolean = false,
+        val expectedTypeMismatchIsReportedInChecker: Boolean = false,
+    ) : ResolutionMode()
 
     class WithStatus(val status: FirDeclarationStatus) : ResolutionMode()
 
@@ -29,8 +34,13 @@ fun ResolutionMode.expectedType(components: BodyResolveComponents): FirTypeRef?
     else -> null
 }
 
-fun withExpectedType(expectedTypeRef: FirTypeRef?): ResolutionMode =
-    expectedTypeRef?.let { ResolutionMode.WithExpectedType(it) } ?: ResolutionMode.ContextDependent
+fun withExpectedType(expectedTypeRef: FirTypeRef?, expectedTypeMismatchIsReportedInChecker: Boolean = false): ResolutionMode =
+    expectedTypeRef?.let {
+        ResolutionMode.WithExpectedType(
+            it,
+            expectedTypeMismatchIsReportedInChecker = expectedTypeMismatchIsReportedInChecker
+        )
+    } ?: ResolutionMode.ContextDependent
 
 @JvmName("withExpectedTypeNullable")
 fun withExpectedType(coneType: ConeKotlinType?, mayBeCoercionToUnitApplied: Boolean = false): ResolutionMode {

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

@@ -31,8 +31,6 @@ import org.jetbrains.kotlin.fir.resolve.transformers.body.resolve.resultType
 import org.jetbrains.kotlin.fir.resolve.typeFromCallee
 import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.*
-import org.jetbrains.kotlin.fir.types.builder.buildErrorTypeRef
-import org.jetbrains.kotlin.fir.types.builder.buildResolvedTypeRef
 import org.jetbrains.kotlin.fir.types.impl.ConeClassLikeTypeImpl
 import org.jetbrains.kotlin.fir.visitors.transformSingle
 import org.jetbrains.kotlin.name.Name
@@ -56,13 +54,26 @@ class FirCallCompleter(
 
     data class CompletionResult<T>(val result: T, val callCompleted: Boolean)
 
-    fun <T> completeCall(call: T, expectedTypeRef: FirTypeRef?): CompletionResult<T> where T : FirResolvable, T : FirStatement =
-        completeCall(call, expectedTypeRef, mayBeCoercionToUnitApplied = false)
+    fun <T> completeCall(
+        call: T,
+        expectedTypeRef: FirTypeRef?,
+        expectedTypeMismatchIsReportedInChecker: Boolean = false,
+    ): CompletionResult<T> where T : FirResolvable, T : FirStatement =
+        completeCall(call, expectedTypeRef, mayBeCoercionToUnitApplied = false, expectedTypeMismatchIsReportedInChecker)
 
     fun <T> completeCall(call: T, data: ResolutionMode): CompletionResult<T> where T : FirResolvable, T : FirStatement =
-        completeCall(call, data.expectedType(components), (data as? ResolutionMode.WithExpectedType)?.mayBeCoercionToUnitApplied == true)
+        completeCall(
+            call,
+            data.expectedType(components),
+            (data as? ResolutionMode.WithExpectedType)?.mayBeCoercionToUnitApplied == true,
+            (data as? ResolutionMode.WithExpectedType)?.expectedTypeMismatchIsReportedInChecker == true,
+        )
 
-    fun <T> completeCall(call: T, expectedTypeRef: FirTypeRef?, mayBeCoercionToUnitApplied: Boolean): CompletionResult<T>
+    private fun <T> completeCall(
+        call: T, expectedTypeRef: FirTypeRef?,
+        mayBeCoercionToUnitApplied: Boolean,
+        expectedTypeMismatchIsReportedInChecker: Boolean,
+    ): CompletionResult<T>
             where T : FirResolvable, T : FirStatement {
         val typeRef = components.typeFromCallee(call)
 
@@ -82,14 +93,15 @@ class FirCallCompleter(
         }
 
         if (expectedTypeRef is FirResolvedTypeRef) {
+            val expectedTypeConstraintPosition = ConeExpectedTypeConstraintPosition(expectedTypeMismatchIsReportedInChecker)
             if (expectedTypeRef.coneType.isUnitOrFlexibleUnit && mayBeCoercionToUnitApplied) {
                 if (candidate.system.notFixedTypeVariables.isNotEmpty()) {
                     candidate.system.addSubtypeConstraintIfCompatible(
-                        initialType, expectedTypeRef.type, ConeExpectedTypeConstraintPosition()
+                        initialType, expectedTypeRef.type, expectedTypeConstraintPosition
                     )
                 }
             } else {
-                candidate.system.addSubtypeConstraint(initialType, expectedTypeRef.type, ConeExpectedTypeConstraintPosition())
+                candidate.system.addSubtypeConstraint(initialType, expectedTypeRef.type, expectedTypeConstraintPosition)
             }
         }
 

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/model/FirConstraintPositionAndErrors.kt

@@ -17,7 +17,9 @@ class ConeFixVariableConstraintPosition(variable: TypeVariableMarker) : FixVaria
 
 class ConeArgumentConstraintPosition(argument: FirElement) : ArgumentConstraintPosition<FirElement>(argument)
 
-class ConeExpectedTypeConstraintPosition : ExpectedTypeConstraintPosition<Nothing?>(null)
+class ConeExpectedTypeConstraintPosition(
+    val expectedTypeMismatchIsReportedInChecker: Boolean
+) : ExpectedTypeConstraintPosition<Nothing?>(null)
 
 class ConeExplicitTypeParameterConstraintPosition(
     typeArgument: FirTypeProjection,

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -423,7 +423,11 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
         }
 
         fun chooseOperator(): FirStatement {
-            callCompleter.completeCall(resolvedOperatorCall, lhsVariable?.returnTypeRef ?: noExpectedType)
+            callCompleter.completeCall(
+                resolvedOperatorCall,
+                lhsVariable?.returnTypeRef ?: noExpectedType,
+                expectedTypeMismatchIsReportedInChecker = true
+            )
             dataFlowAnalyzer.exitFunctionCall(resolvedOperatorCall, callCompleted = true)
             val assignment =
                 buildVariableAssignment {
@@ -684,7 +688,10 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
         val resolvedAssignment = callResolver.resolveVariableAccessAndSelectCandidate(variableAssignment)
         val result = if (resolvedAssignment is FirVariableAssignment) {
             val completeAssignment = callCompleter.completeCall(resolvedAssignment, noExpectedType).result // TODO: check
-            completeAssignment.transformRValue(transformer, withExpectedType(variableAssignment.lValueTypeRef))
+            completeAssignment.transformRValue(
+                transformer,
+                withExpectedType(variableAssignment.lValueTypeRef, expectedTypeMismatchIsReportedInChecker = true),
+            )
         } else {
             // This can happen in erroneous code only
             resolvedAssignment