[Test] Add helpers file with functions for inference testing

compiler/testData/diagnostics/helpers/inference/inferenceUtils.kt

@@ -0,0 +1,3 @@
+fun <K> id(x: K): K = x
+fun <K> materialize(): K = null!!
+fun <K> select(vararg values: K): K = values[0]

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/directives/AdditionalFilesDirectives.kt

@@ -44,4 +44,11 @@ object AdditionalFilesDirectives : SimpleDirectivesContainer() {
             See directory ./compiler/tests-spec/helpers/
         """.trimIndent()
     )
+
+    val INFERENCE_HELPERS by directive(
+        description = """
+            Adds util functions for type checking
+            See file ./compiler/testData/diagnostics/helpers/inference/inferenceUtils.kt
+        """.trimIndent()
+    )
 }

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/services/sourceProviders/AdditionalDiagnosticsSourceFilesProvider.kt

@@ -6,8 +6,11 @@
 package org.jetbrains.kotlin.test.services.sourceProviders
 
 import org.jetbrains.kotlin.test.directives.AdditionalFilesDirectives
+import org.jetbrains.kotlin.test.directives.AdditionalFilesDirectives.CHECK_TYPE
+import org.jetbrains.kotlin.test.directives.AdditionalFilesDirectives.INFERENCE_HELPERS
 import org.jetbrains.kotlin.test.directives.model.DirectivesContainer
 import org.jetbrains.kotlin.test.directives.model.RegisteredDirectives
+import org.jetbrains.kotlin.test.directives.model.SimpleDirective
 import org.jetbrains.kotlin.test.model.TestFile
 import org.jetbrains.kotlin.test.model.TestModule
 import org.jetbrains.kotlin.test.services.AdditionalSourceProvider
@@ -17,7 +20,10 @@ import java.io.File
 class AdditionalDiagnosticsSourceFilesProvider(testServices: TestServices) : AdditionalSourceProvider(testServices) {
     companion object {
         private const val HELPERS_PATH = "./compiler/testData/diagnostics/helpers"
-        private const val CHECK_TYPE_PATH = "$HELPERS_PATH/types/checkType.kt"
+        private val DIRECTIVE_TO_FILE_MAP: Map<SimpleDirective, String> = mapOf(
+            CHECK_TYPE to "$HELPERS_PATH/types/checkType.kt",
+            INFERENCE_HELPERS to "$HELPERS_PATH/inference/inferenceUtils.kt"
+        )
     }
 
     override val directives: List<DirectivesContainer> =
@@ -26,8 +32,10 @@ class AdditionalDiagnosticsSourceFilesProvider(testServices: TestServices) : Add
     @OptIn(ExperimentalStdlibApi::class)
     override fun produceAdditionalFiles(globalDirectives: RegisteredDirectives, module: TestModule): List<TestFile> {
         return buildList {
-            if (containsDirective(globalDirectives, module, AdditionalFilesDirectives.CHECK_TYPE)) {
-                add(File(CHECK_TYPE_PATH).toTestFile())
+            for ((directive, path) in DIRECTIVE_TO_FILE_MAP) {
+                if (directive in module.directives) {
+                    add(File(path).toTestFile())
+                }
             }
         }
     }