From 4128d2751004aa34a54e1ab35daaf7e360a749f0 Mon Sep 17 00:00:00 2001
From: pyos <pyos@google.com>
Date: Tue, 1 Jun 2021 11:52:30 +0200
Subject: [PATCH] JVM_IR: do not use invokedynamic for inline fun references

---
 .../jvm/lower/indy/LambdaMetafactoryArguments.kt   | 12 ++++++++----
 .../codegen/box/invokedynamic/sam/inlineOnly.kt    | 14 ++++++++++----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
index 93465d64943..1c73860d41f 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
@@ -29,7 +29,6 @@ import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.resolve.inline.INLINE_ONLY_ANNOTATION_FQ_NAME
 import org.jetbrains.kotlin.types.Variance
 import org.jetbrains.kotlin.utils.addIfNotNull
 
@@ -76,20 +75,25 @@ internal class LambdaMetafactoryArgumentsBuilder(
         if (samClass.requiresDelegationToDefaultImpls())
             return null
 
+        // TODO in cases where LambdaMetafactory is unusable directly due to problems with the implementation function,
+        //      we can still avoid generating an entire class by converting the function reference into a lambda first;
+        //      see `InlineCallableReferenceToLambdaPhase`
         val implFun = reference.symbol.owner
 
         // Don't generate references to intrinsic functions as invokedynamic (no such method exists at run-time).
         if (context.irIntrinsics.getIntrinsic(implFun.symbol) != null)
             return null
 
-        // Don't generate reference to inlineOnly methods as those do not exist at runtime.
-        if (implFun.hasAnnotation(INLINE_ONLY_ANNOTATION_FQ_NAME))
+        // Can't use invokedynamic if the referenced function has to be inlined for correct semantics
+        // Also in some cases like `private inline fun` we'd need accessors, which `SyntheticAccessorLowering`
+        // won't generate under the assumption that the inline function will be inlined. Plus if the function
+        // is in a different module we should probably copy it anyway (and regenerate all objects in it).
+        if (implFun.isInline)
             return null
 
         if (implFun is IrConstructor && implFun.visibility.isPrivate) {
             // Kotlin generates constructor accessors differently from Java.
             // TODO more precise accessibility check (see SyntheticAccessorLowering::isAccessible)
-            // TODO wrap inaccessible constructor with a local function
             return null
         }
 
diff --git a/compiler/testData/codegen/box/invokedynamic/sam/inlineOnly.kt b/compiler/testData/codegen/box/invokedynamic/sam/inlineOnly.kt
index 2cf07f19a0c..0cada45869f 100644
--- a/compiler/testData/codegen/box/invokedynamic/sam/inlineOnly.kt
+++ b/compiler/testData/codegen/box/invokedynamic/sam/inlineOnly.kt
@@ -10,11 +10,17 @@
 
 import java.util.function.Consumer
 
-fun call(c: Consumer<String>) {
-}
+inline fun <reified T> f(x: T) =
+    println("${T::class.simpleName}($x)")
+
+private inline fun g(x: String) = println(x)
+
+fun call(c: Consumer<String>) = c.accept("")
 
 fun box(): String {
-    // println is inline only and therefore we cannot use invoke-dynamic to target it.
-    call(::println)
+    call(::println) // `println` is `@InlineOnly`
+    call(::f) // `f` has a reified type parameter and thus isn't callable directly
+    val obj = { call(::g) } // `g` is inaccessible in this scope
+    obj()
     return "OK"
 }