FIR IDE: render KtFunctionalType in KtTypeRenderer

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/components/KtTypeRenderer.kt

@@ -16,10 +16,16 @@ abstract class KtTypeRenderer : KtAnalysisSessionComponent() {
 
 data class KtTypeRendererOptions(
     val renderFqNames: Boolean,
+    val renderFunctionTypes: Boolean
 ) {
     companion object {
         val DEFAULT = KtTypeRendererOptions(
-            renderFqNames = true
+            renderFqNames = true,
+            renderFunctionTypes = true,
+        )
+        val SHORT_NAMES = KtTypeRendererOptions(
+            renderFqNames = false,
+            renderFunctionTypes = true,
         )
     }
 }
@@ -33,9 +39,7 @@ class KtDefaultTypeRenderer(override val analysisSession: KtAnalysisSession, ove
         when (type) {
             is KtDenotableType -> when (type) {
                 is KtClassType -> {
-                    render(type.classId, options)
+                    renderClassType(type, options)
-                    renderTypeArgumentsIfNotEmpty(type.typeArguments, options)
-                    renderNullability(type.nullability)
                 }
                 is KtTypeParameterType -> {
                     append(type.name.asString())
@@ -64,6 +68,67 @@ class KtDefaultTypeRenderer(override val analysisSession: KtAnalysisSession, ove
         }
     }
 
+    private fun StringBuilder.renderClassType(
+        type: KtClassType,
+        options: KtTypeRendererOptions
+    ) {
+        when {
+            type is KtUsualClassType || !options.renderFunctionTypes -> {
+                renderClassTypeAsNonFunctional(type, options)
+            }
+            type is KtFunctionalType -> {
+                renderFunctionalType(type, options)
+            }
+        }
+    }
+
+    private fun StringBuilder.renderClassTypeAsNonFunctional(
+        type: KtClassType,
+        options: KtTypeRendererOptions
+    ) {
+        render(type.classId, options)
+        renderTypeArgumentsIfNotEmpty(type.typeArguments, options)
+        renderNullability(type.nullability)
+    }
+
+    private fun StringBuilder.renderFunctionalType(
+        type: KtFunctionalType,
+        options: KtTypeRendererOptions
+    ) {
+        wrapIf(type.nullability == KtTypeNullability.NULLABLE, left = "(", right = ")?") {
+            if (type.isSuspend) append("suspend ")
+            renderReceiverTypeOfFunctionalType(type, options)
+            renderParametersOfFunctionalType(type, options)
+            append(" -> ")
+            render(type.typeArguments.last(), options)
+        }
+    }
+
+    private fun StringBuilder.renderReceiverTypeOfFunctionalType(
+        type: KtFunctionalType,
+        options: KtTypeRendererOptions
+    ) {
+        type.receiverType?.let { receiverType ->
+            render(receiverType, options)
+            append(".")
+        }
+    }
+
+    private fun StringBuilder.renderParametersOfFunctionalType(
+        type: KtFunctionalType,
+        options: KtTypeRendererOptions
+    ) {
+        append("(")
+        val parameterTypes = type.parameterTypes
+        type.parameterTypes.forEachIndexed { index, parameterType ->
+            render(parameterType, options)
+            if (index != parameterTypes.lastIndex) {
+                append(", ")
+            }
+        }
+        append(")")
+    }
+
     private fun StringBuilder.renderTypeArgumentsIfNotEmpty(typeArguments: List<KtTypeArgument>, options: KtTypeRendererOptions) {
         if (typeArguments.isNotEmpty()) {
             append("<")
@@ -113,4 +178,10 @@ class KtDefaultTypeRenderer(override val analysisSession: KtAnalysisSession, ove
         render()
         append(")")
     }
+
+    private inline fun StringBuilder.wrapIf(condition: Boolean, left: String, right: String, render: StringBuilder.() -> Unit) {
+        if (condition) append(left)
+        render()
+        if (condition) append(right)
+    }
 }

idea/idea-frontend-fir/tests/org/jetbrains/kotlin/idea/frontend/api/types/KtTypeRendererTest.kt

@@ -83,7 +83,7 @@ class KtTypeRendererTest : KotlinLightCodeInsightFixtureTestCase() {
             type = "Map<List<Int?>, V?>?",
             expected = "Map<List<Int?>, V?>?",
             typeArguments = listOf("V"),
-            rendererOptions = KtTypeRendererOptions(renderFqNames = false)
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
         )
     }
 
@@ -91,7 +91,55 @@ class KtTypeRendererTest : KotlinLightCodeInsightFixtureTestCase() {
         doTestByExpression(
             expression = "java.lang.String.CASE_INSENSITIVE_ORDER",
             expected = "(Comparator<(String..String?)>..Comparator<(String..String?)>?)",
-            rendererOptions = KtTypeRendererOptions(renderFqNames = false)
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testFunctionalType() {
+        doTestByTypeText(
+            type = "(String, Int?) -> Long",
+            expected = "(String, Int?) -> Long",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testNullableFunctionalType() {
+        doTestByTypeText(
+            type = "((String, Int?) -> Long)?",
+            expected = "((String, Int?) -> Long)?",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testFunctionalTypeNoArguments() {
+        doTestByTypeText(
+            type = "() -> Long",
+            expected = "() -> Long",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testFunctionalTypeReceiver() {
+        doTestByTypeText(
+            type = "Int.(String) -> Long",
+            expected = "Int.(String) -> Long",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testFunctionalTypeUnitReturnType() {
+        doTestByTypeText(
+            type = "(String) -> Unit",
+            expected = "(String) -> Unit",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
+        )
+    }
+
+    fun testFunctionalTypeRenderAsUsualClassType() {
+        doTestByTypeText(
+            type = "Int.(String, Long) -> Char",
+            expected = "Function3<Int, String, Long, Char>",
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES.copy(renderFunctionTypes = false)
         )
     }
 
@@ -103,7 +151,7 @@ class KtTypeRendererTest : KotlinLightCodeInsightFixtureTestCase() {
                 if (x is String && x is Int) x else null
             }""".trimIndent(),
             expected = "(String?&Int?)",
-            rendererOptions = KtTypeRendererOptions(renderFqNames = false)
+            rendererOptions = KtTypeRendererOptions.SHORT_NAMES
         )
     }
 }