Avoid skipping lambda argument processing in case of explicit type param

#KT-38691 fixed

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

@@ -11561,6 +11561,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
                 runTest("compiler/testData/diagnostics/tests/inference/regressions/kt37650.kt");
             }
 
+            @TestMetadata("kt38691.kt")
+            public void testKt38691() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/regressions/kt38691.kt");
+            }
+
             @TestMetadata("kt4420.kt")
             public void testKt4420() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inference/regressions/kt4420.kt");

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

@@ -20,11 +20,10 @@ import org.jetbrains.kotlin.builtins.*
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemBuilder
 import org.jetbrains.kotlin.resolve.calls.inference.components.NewTypeSubstitutor
-import org.jetbrains.kotlin.resolve.calls.inference.model.ArgumentConstraintPosition
-import org.jetbrains.kotlin.resolve.calls.inference.model.LHSArgumentConstraintPosition
-import org.jetbrains.kotlin.resolve.calls.inference.model.TypeVariableForLambdaReturnType
+import org.jetbrains.kotlin.resolve.calls.inference.model.*
 import org.jetbrains.kotlin.resolve.calls.model.*
 import org.jetbrains.kotlin.types.ErrorUtils
+import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.UnwrappedType
 import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.types.typeUtil.builtIns
@@ -63,8 +62,20 @@ private fun preprocessLambdaArgument(
     forceResolution: Boolean = false,
     returnTypeVariable: TypeVariableForLambdaReturnType? = null
 ): ResolvedAtom {
-    if (expectedType != null && !forceResolution && csBuilder.isTypeVariable(expectedType)) {
-        return LambdaWithTypeVariableAsExpectedTypeAtom(argument, expectedType)
+
+    if (expectedType != null && !forceResolution) {
+        // postpone lambda processing if expected type is a type variable that could be fixed into something non-trivial
+        val expectedTypeVariableWithConstraints = csBuilder.currentStorage().notFixedTypeVariables[expectedType.constructor]
+
+        if (expectedTypeVariableWithConstraints != null) {
+            val explicitTypeArgument = expectedTypeVariableWithConstraints.constraints.find {
+                it.kind == ConstraintKind.EQUALITY && it.position.from is ExplicitTypeParameterConstraintPosition
+            }?.type as? KotlinType
+
+            if (explicitTypeArgument == null || explicitTypeArgument.arguments.isNotEmpty()) {
+                return LambdaWithTypeVariableAsExpectedTypeAtom(argument, expectedType)
+            }
+        }
     }
 
     val resolvedArgument = extractLambdaInfoFromFunctionalType(expectedType, argument, returnTypeVariable)

compiler/testData/diagnostics/tests/inference/regressions/kt38691.fir.kt

@@ -0,0 +1,14 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+class Inv<T>
+fun <T> materializeInv() = Inv<T>()
+fun <X> foo(x: Inv<X>, y: X) = materializeInv<X>()
+fun <X> foo(x: Inv<X>, y: () -> X) = materializeInv<X>()
+
+fun <R> main(fn: () -> R) {
+    fun bar(): R = null as R
+    val x1 = foo<R>(materializeInv()) { fn() } // OVERLOAD_RESOLUTION_AMBIGUITY only in NI
+    val x2 = foo<R>(materializeInv(), fn) // OK
+    val x3 = foo<R>(materializeInv(), ::bar) // OK
+}

compiler/testData/diagnostics/tests/inference/regressions/kt38691.kt

@@ -0,0 +1,14 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+class Inv<T>
+fun <T> materializeInv() = Inv<T>()
+fun <X> foo(x: Inv<X>, y: X) = materializeInv<X>()
+fun <X> foo(x: Inv<X>, y: () -> X) = materializeInv<X>()
+
+fun <R> main(fn: () -> R) {
+    fun bar(): R = null <!UNCHECKED_CAST!>as R<!>
+    val x1 = foo<R>(materializeInv()) { fn() } // OVERLOAD_RESOLUTION_AMBIGUITY only in NI
+    val x2 = foo<R>(materializeInv(), fn) // OK
+    val x3 = foo<R>(materializeInv(), ::bar) // OK
+}

compiler/testData/diagnostics/tests/inference/regressions/kt38691.txt

@@ -0,0 +1,13 @@
+package
+
+public fun </*0*/ X> foo(/*0*/ x: Inv<X>, /*1*/ y: () -> X): Inv<X>
+public fun </*0*/ X> foo(/*0*/ x: Inv<X>, /*1*/ y: X): Inv<X>
+public fun </*0*/ R> main(/*0*/ fn: () -> R): kotlin.Unit
+public fun </*0*/ T> materializeInv(): Inv<T>
+
+public final class Inv</*0*/ T> {
+    public constructor Inv</*0*/ T>()
+    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/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -11568,6 +11568,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTestWithFirVali
                     runTest("compiler/testData/diagnostics/tests/inference/regressions/kt37650.kt");
                 }
 
+                @TestMetadata("kt38691.kt")
+                public void testKt38691() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/regressions/kt38691.kt");
+                }
+
                 @TestMetadata("kt4420.kt")
                 public void testKt4420() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/regressions/kt4420.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -11563,6 +11563,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/inference/regressions/kt37650.kt");
                 }
 
+                @TestMetadata("kt38691.kt")
+                public void testKt38691() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/regressions/kt38691.kt");
+                }
+
                 @TestMetadata("kt4420.kt")
                 public void testKt4420() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/regressions/kt4420.kt");