Put using underscored type arguments under a feature

compiler/testData/codegen/box/underscoredTypeArguments/backTicked.kt

@@ -1,3 +1,4 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
 // WITH_RUNTIME
 
 fun <K, T> foo(x: (K) -> T): Pair<K, T> = (1 as K) to (1f as T)

compiler/testData/codegen/box/underscoredTypeArguments/dependentTypeParameters.kt

@@ -1,3 +1,4 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
 // WITH_RUNTIME
 // TARGET_BACKEND: JVM
 

compiler/testData/codegen/box/underscoredTypeArguments/lambdaInputType.kt

@@ -1,3 +1,5 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
+
 sealed class MyResult<out T>{
     data class Success<T>(val value: T): MyResult<T>()
     data class Failure(val exception: Throwable): MyResult<Nothing>()

compiler/testData/codegen/box/underscoredTypeArguments/react.kt

@@ -1,3 +1,5 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
+
 interface RProps
 open class RComponent<K, T> : Component<K, T>
 interface RState

compiler/testData/codegen/box/underscoredTypeArguments/simple.kt

@@ -1,3 +1,4 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
 // WITH_RUNTIME
 
 fun <K, T> foo(x: (K) -> T): Pair<K, T> = (1 as K) to (1f as T)

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

@@ -1,3 +1,4 @@
+// !LANGUAGE: +PartiallySpecifiedTypeArguments
 // !DIAGNOSTICS: -UNCHECKED_CAST
 // FIR_IDENTICAL
 // WITH_RUNTIME

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

@@ -0,0 +1,10 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNCHECKED_CAST
+// WITH_RUNTIME
+
+fun <K, T> foo(x: (K) -> T): Pair<K, T> = (1 as K) to (1f as T)
+
+fun box(): String {
+    val x = foo<Int, <!UNRESOLVED_REFERENCE!>_<!>> { it.toFloat() } // Pair<Int, Float>
+    return "OK"
+}

compiler/testData/diagnostics/tests/inference/underscoredTypeArgument.txt

@@ -0,0 +1,4 @@
+package
+
+public fun box(): kotlin.String
+public fun </*0*/ K, /*1*/ T> foo(/*0*/ x: (K) -> T): kotlin.Pair<K, T>