[NI] Improvements for "not enough information" diagnostic

#KT-30590 Fixed

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

@@ -63,6 +63,11 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext {
         return this is ConeClassErrorType || this is ConeKotlinErrorType || this.typeConstructor() is ErrorTypeConstructor
     }
 
+    override fun KotlinTypeMarker.isUninferredParameter(): Boolean {
+        assert(this is ConeKotlinType)
+        return false // TODO
+    }
+
     override fun FlexibleTypeMarker.asDynamicType(): DynamicTypeMarker? {
         assert(this is ConeKotlinType)
         return null // TODO

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/DiagnosticReporterByTrackingStrategy.kt

@@ -229,6 +229,7 @@ class DiagnosticReporterByTrackingStrategy(
                     trace.report(UPPER_BOUND_VIOLATED.on(typeArgumentReference, constraintError.upperKotlinType, constraintError.lowerKotlinType))
                 }
             }
+
             CapturedTypeFromSubtyping::class.java -> {
                 val capturedError = diagnostic as CapturedTypeFromSubtyping
                 val position = capturedError.position
@@ -248,6 +249,9 @@ class DiagnosticReporterByTrackingStrategy(
             }
 
             NotEnoughInformationForTypeParameter::class.java -> {
+                if (allDiagnostics.any {it is ConstrainingTypeIsError || it is NewConstraintError || it is WrongCountOfTypeArguments})
+                    return
+
                 val error = diagnostic as NotEnoughInformationForTypeParameter
                 val call = error.resolvedAtom.atom?.safeAs<PSIKotlinCall>()?.psiCall ?: call
                 val expression = call.calleeExpression ?: return
@@ -256,7 +260,7 @@ class DiagnosticReporterByTrackingStrategy(
                     is TypeVariableForLambdaReturnType -> "return type of lambda"
                     else -> error("Unsupported type variable: $typeVariable")
                 }
-                trace.report(NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER.on(expression, typeVariableName))
+                trace.reportDiagnosticOnce(NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER.on(expression, typeVariableName))
             }
         }
     }

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

@@ -166,6 +166,11 @@ class ConstraintInjector(val constraintIncorporator: ConstraintIncorporator, val
                     ?: error("Should by type variableConstructor: $typeVariableConstructor. ${c.allTypeVariables.values}")
 
             var targetType = type
+            if (targetType.isUninferredParameter()) {
+                // there already should be an error, so there is no point in reporting one more
+                return
+            }
+
             if (targetType.isError()) {
                 c.addError(ConstrainingTypeIsError(typeVariable, targetType, position))
                 return

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

@@ -6,8 +6,10 @@
 package org.jetbrains.kotlin.resolve.calls.inference.components
 
 import org.jetbrains.kotlin.resolve.calls.inference.model.NotEnoughInformationForTypeParameter
+import org.jetbrains.kotlin.resolve.calls.inference.model.TypeVariableFromCallableDescriptor
 import org.jetbrains.kotlin.resolve.calls.inference.model.VariableWithConstraints
 import org.jetbrains.kotlin.resolve.calls.model.*
+import org.jetbrains.kotlin.types.ErrorUtils
 import org.jetbrains.kotlin.types.TypeConstructor
 import org.jetbrains.kotlin.types.UnwrappedType
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker
@@ -84,11 +86,11 @@ class KotlinConstraintSystemCompleter(
             if (variableForFixation.hasProperConstraint || completionMode == ConstraintSystemCompletionMode.FULL) {
                 val variableWithConstraints = c.notFixedTypeVariables.getValue(variableForFixation.variable)
 
-                fixVariable(c, topLevelType, variableWithConstraints, postponedKtPrimitives)
+                if (variableForFixation.hasProperConstraint)
+                    fixVariable(c, topLevelType, variableWithConstraints, postponedKtPrimitives)
+                else
+                    processVariableWhenNotEnoughInformation(c, variableWithConstraints, topLevelAtoms)
 
-                if (!variableForFixation.hasProperConstraint) {
-                    c.addError(NotEnoughInformationForTypeParameter(variableWithConstraints.typeVariable, topLevelAtoms.first()))
-                }
                 continue
             }
 
@@ -218,4 +220,51 @@ class KotlinConstraintSystemCompleter(
         val resultType = resultTypeResolver.findResultType(c, variableWithConstraints, direction)
         c.fixVariable(variableWithConstraints.typeVariable, resultType)
     }
+
+    private fun processVariableWhenNotEnoughInformation(
+        c: Context,
+        variableWithConstraints: VariableWithConstraints,
+        topLevelAtoms: List<ResolvedAtom>
+    ) {
+        val typeVariable = variableWithConstraints.typeVariable
+
+        val resolvedAtom = findResolvedAtomBy(typeVariable, topLevelAtoms) ?: topLevelAtoms.firstOrNull()
+        if (resolvedAtom != null) {
+            c.addError(NotEnoughInformationForTypeParameter(typeVariable, resolvedAtom))
+        }
+
+        val resultErrorType = if (typeVariable is TypeVariableFromCallableDescriptor)
+            ErrorUtils.createUninferredParameterType(typeVariable.originalTypeParameter)
+        else
+            ErrorUtils.createErrorType("Cannot infer type variable $typeVariable")
+
+        c.fixVariable(typeVariable, resultErrorType)
+    }
+
+    private fun findResolvedAtomBy(typeVariable: TypeVariableMarker, topLevelAtoms: List<ResolvedAtom>): ResolvedAtom? {
+        fun ResolvedAtom.check(): ResolvedAtom? {
+            val suitableCall = when (this) {
+                is ResolvedCallAtom -> typeVariable in substitutor.freshVariables
+                is ResolvedCallableReferenceAtom -> candidate?.freshSubstitutor?.freshVariables?.let { typeVariable in it } ?: false
+                is ResolvedLambdaAtom -> typeVariable == typeVariableForLambdaReturnType
+                else -> false
+            }
+
+            if (suitableCall) {
+                return this
+            }
+
+            subResolvedAtoms.forEach { subResolvedAtom ->
+                subResolvedAtom.check()?.let { result -> return@check result }
+            }
+
+            return null
+        }
+
+        for (topLevelAtom in topLevelAtoms) {
+            topLevelAtom.check()?.let { return it }
+        }
+
+        return null
+    }
 }

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

@@ -18,10 +18,7 @@ package org.jetbrains.kotlin.resolve.calls.inference.components
 
 import org.jetbrains.kotlin.resolve.calls.NewCommonSuperTypeCalculator
 import org.jetbrains.kotlin.resolve.calls.inference.components.TypeVariableDirectionCalculator.ResolveDirection
-import org.jetbrains.kotlin.resolve.calls.inference.model.Constraint
+import org.jetbrains.kotlin.resolve.calls.inference.model.*
-import org.jetbrains.kotlin.resolve.calls.inference.model.ConstraintKind
-import org.jetbrains.kotlin.resolve.calls.inference.model.VariableWithConstraints
-import org.jetbrains.kotlin.resolve.calls.inference.model.checkConstraint
 import org.jetbrains.kotlin.resolve.constants.IntegerLiteralTypeConstructor
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/model/MutableConstraintStorage.kt

@@ -5,12 +5,9 @@
 
 package org.jetbrains.kotlin.resolve.calls.inference.model
 
-import org.jetbrains.kotlin.resolve.calls.inference.components.NewTypeSubstitutor
 import org.jetbrains.kotlin.resolve.calls.inference.trimToSize
 import org.jetbrains.kotlin.resolve.calls.model.KotlinCallDiagnostic
 import org.jetbrains.kotlin.resolve.calls.tower.isSuccess
-import org.jetbrains.kotlin.types.TypeConstructor
-import org.jetbrains.kotlin.types.UnwrappedType
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker
 import org.jetbrains.kotlin.types.model.TypeConstructorMarker
 import org.jetbrains.kotlin.types.model.TypeVariableMarker
@@ -38,16 +35,22 @@ class MutableVariableWithConstraints(
     fun addConstraint(constraint: Constraint): Constraint? {
         val previousConstraintWithSameType = constraints.filter { it.typeHashCode == constraint.typeHashCode && it.type == constraint.type }
 
-        if (previousConstraintWithSameType.any { newConstraintIsUseless(it.kind, constraint.kind) }) {
+        if (previousConstraintWithSameType.any { previous -> newConstraintIsUseless(previous, constraint) })
             return null
+
+        val addAsEqualityConstraint = previousConstraintWithSameType.any { previous ->
+            when (previous.kind) {
+                ConstraintKind.LOWER -> constraint.kind.isUpper()
+                ConstraintKind.UPPER -> constraint.kind.isLower()
+                ConstraintKind.EQUALITY -> true
+            }
         }
 
-        val actualConstraint = if (previousConstraintWithSameType.isNotEmpty()) {
+        val actualConstraint = if (addAsEqualityConstraint)
-            // i.e. previous is LOWER and new is UPPER or opposite situation
             Constraint(ConstraintKind.EQUALITY, constraint.type, constraint.position, constraint.typeHashCode)
-        } else {
+        else
             constraint
-        }
+
         mutableConstraints.add(actualConstraint)
         simplifiedConstraints = null
         return actualConstraint
@@ -66,18 +69,47 @@ class MutableVariableWithConstraints(
         simplifiedConstraints = null
     }
 
-    private fun newConstraintIsUseless(oldKind: ConstraintKind, newKind: ConstraintKind) =
+    private fun newConstraintIsUseless(old: Constraint, new: Constraint): Boolean {
-        when (oldKind) {
+        // Constraints from declared upper bound are quite special -- they aren't considered as a proper ones
+        // In other words, user-defined constraints have "higher" priority and here we're trying not to loose them
+        if (old.position.from is DeclaredUpperBoundConstraintPosition && new.position.from !is DeclaredUpperBoundConstraintPosition)
+            return false
+
+        return when (old.kind) {
             ConstraintKind.EQUALITY -> true
-            ConstraintKind.LOWER -> newKind == ConstraintKind.LOWER
+            ConstraintKind.LOWER -> new.kind.isLower()
-            ConstraintKind.UPPER -> newKind == ConstraintKind.UPPER
+            ConstraintKind.UPPER -> new.kind.isUpper()
         }
+    }
 
     private fun simplifyConstraints(): List<Constraint> {
-        val equalityConstraints = mutableConstraints
+        val distinctConstraints = removeDuplicatesFromDeclaredUpperBoundConstraints(mutableConstraints)
+
+        val equalityConstraints = distinctConstraints
             .filter { it.kind == ConstraintKind.EQUALITY }
             .groupBy { it.typeHashCode }
-        return mutableConstraints.filter { isUsefulConstraint(it, equalityConstraints) }
+        return distinctConstraints.filter { isUsefulConstraint(it, equalityConstraints) }
+    }
+
+    private fun removeDuplicatesFromDeclaredUpperBoundConstraints(constraints: List<Constraint>): MutableList<Constraint> {
+        val currentConstraints = constraints.toMutableList()
+        val iterator = currentConstraints.iterator()
+        while (iterator.hasNext()) {
+            val potentialDuplicate = iterator.next()
+
+            if (potentialDuplicate.position.from !is DeclaredUpperBoundConstraintPosition) continue
+            val hasDuplicate = currentConstraints.any { other ->
+                potentialDuplicate !== other &&
+                        potentialDuplicate.typeHashCode == other.typeHashCode &&
+                        potentialDuplicate.type == other.type &&
+                        potentialDuplicate.kind == other.kind
+            }
+
+            if (hasDuplicate)
+                iterator.remove()
+        }
+
+        return currentConstraints
     }
 
     private fun isUsefulConstraint(constraint: Constraint, equalityConstraints: Map<Int, List<Constraint>>): Boolean {

compiler/testData/diagnostics/tests/generics/kt30590.kt

@@ -1,11 +1,9 @@
 // !WITH_NEW_INFERENCE
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
-// !LANGUAGE: +NewInference
+// NI_EXPECTED_FILE
-// Issue: KT-30590
 
 interface A
 fun <T: A, R: T> emptyStrangeMap(): Map<T, R> = TODO()
 fun test7() : Map<A, A> = emptyStrangeMap()
 
-fun test() = emptyStrangeMap()
+fun test() = <!NI;NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, OI;TYPE_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>emptyStrangeMap<!>()
-

compiler/testData/diagnostics/tests/generics/kt30590.ni.txt

@@ -0,0 +1,11 @@
+package
+
+public fun </*0*/ T : A, /*1*/ R : T> emptyStrangeMap(): kotlin.collections.Map<T, R>
+public fun test(): kotlin.collections.Map<???, ???>
+public fun test7(): kotlin.collections.Map<A, A>
+
+public interface A {
+    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
+}

compiler/testData/diagnostics/tests/generics/kt30590.txt

@@ -1,6 +1,7 @@
 package
 
 public fun </*0*/ T : A, /*1*/ R : T> emptyStrangeMap(): kotlin.collections.Map<T, R>
+public fun test(): [ERROR : Error function type]
 public fun test7(): kotlin.collections.Map<A, A>
 
 public interface A {

compiler/testData/diagnostics/tests/inference/reportingImprovements/inferTypeFromUnresolvedArgument.kt

@@ -2,8 +2,12 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 fun <K> id2(x: K, s: String): K = x
+fun <K> ret(s: String): K = TODO()
 
 fun test() {
-    <!NI;IMPLICIT_NOTHING_AS_TYPE_PARAMETER, NI;NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>id2<!>(<!UNRESOLVED_REFERENCE!>unresolved<!>, "foo")
+    id2(<!UNRESOLVED_REFERENCE!>unresolved<!>, "foo")
-    <!NI;UNREACHABLE_CODE!><!NI;IMPLICIT_NOTHING_AS_TYPE_PARAMETER, NI;NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>id2<!>(<!UNRESOLVED_REFERENCE!>unresolved<!>, <!CONSTANT_EXPECTED_TYPE_MISMATCH!>42<!>)<!>
+    id2(<!UNRESOLVED_REFERENCE!>unresolved<!>, <!CONSTANT_EXPECTED_TYPE_MISMATCH!>42<!>)
+
+    <!NI;NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, OI;TYPE_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>ret<!>("foo")
+    <!OI;TYPE_INFERENCE_PARAMETER_CONSTRAINT_ERROR!>ret<!>(<!CONSTANT_EXPECTED_TYPE_MISMATCH!>42<!>)
 }

compiler/testData/diagnostics/tests/inference/reportingImprovements/inferTypeFromUnresolvedArgument.txt

@@ -1,4 +1,5 @@
 package
 
 public fun </*0*/ K> id2(/*0*/ x: K, /*1*/ s: kotlin.String): K
+public fun </*0*/ K> ret(/*0*/ s: kotlin.String): K
 public fun test(): kotlin.Unit

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

@@ -49,6 +49,11 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext {
         return this.isError
     }
 
+    override fun KotlinTypeMarker.isUninferredParameter(): Boolean {
+        require(this is KotlinType, this::errorMessage)
+        return ErrorUtils.isUninferredParameter(this)
+    }
+
     override fun SimpleTypeMarker.isStubType(): Boolean {
         require(this is SimpleType, this::errorMessage)
         return this is StubType

core/type-system/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -145,6 +145,7 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
     fun KotlinTypeMarker.asFlexibleType(): FlexibleTypeMarker?
 
     fun KotlinTypeMarker.isError(): Boolean
+    fun KotlinTypeMarker.isUninferredParameter(): Boolean
 
     fun FlexibleTypeMarker.asDynamicType(): DynamicTypeMarker?