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Implement Kotlin default interface method forwarding

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Kotlin's implementation of defaults depends on the -Xjvm-default setting (or the @JvmDefault deprecated annotation, not implemented here): by default, actual interface class files don't use default method, and any class that would inherit one instead implements the interface calling a static method defined on TheInterface$DefaultImpls. With
-Xjvm-default=all or =all-compatibility, real interface default methods are emitted, with the latter retaining the DefaultImpls methods so that other Kotlin can use it.

Here I adopt a hybrid solution: create a real default method implementation, but also emit a forwarding method like `@override int f(int x) { return super.TheInterface.f(x); }`, because the Java extractor will see `MyClass.f` in the emitted class file and try to dispatch directly to it. The only downside is that we emit a default interface
method body for a prototype that will appear to be `abstract` to the Java extractor and which it will extract as such. I work around this by tolerating the combination `default abstract` in QL. The alternative would be to fully mimic the DefaultImpls approach, giving 100% fidelity to kotlinc's strategy and therefore no clash with the Java
extractor's view of the world.
This commit is contained in:
Chris Smowton
2022-07-20 10:01:16 +01:00
parent 040d72e7f1
commit e8a35983ee
9 changed files with 137 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

60
java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt
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@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.backend.common.extensions.IrPluginContext
import org.jetbrains.kotlin.backend.common.lower.parents
import org.jetbrains.kotlin.backend.common.pop
import org.jetbrains.kotlin.builtins.functions.BuiltInFunctionArity
import org.jetbrains.kotlin.config.JvmAnalysisFlags
import org.jetbrains.kotlin.descriptors.*
import org.jetbrains.kotlin.descriptors.java.JavaVisibilities
import org.jetbrains.kotlin.ir.IrElement
@@ -828,10 +829,56 @@ open class KotlinFileExtractor(
}
}
private fun needsInterfaceForwarder(f: IrFunction) =
// forAllMethodsWithBody means -Xjvm-default=all or all-compatibility, in which case real Java default interfaces are used, and we don't need to do anything.
// Otherwise, for a method inheriting a default, we need to create a synthetic method like `int f(int x) { return super.InterfaceWithDefault.f(x); }`, because
// kotlinc will generate a public method and Java callers may directly target it.
// (NB. kotlinc's actual implementation strategy is different -- it makes an inner class called InterfaceWithDefault$DefaultImpls and stores the default methods
// there to allow default method usage in Java < 8, but this is hopefully niche.
!pluginContext.languageVersionSettings.getFlag(JvmAnalysisFlags.jvmDefaultMode).forAllMethodsWithBody &&
f.realOverrideTarget.let { it != f && it.parentClassOrNull?.isInterface == true }
private fun makeInterfaceForwarder(f: IrFunction, parentId: Label<out DbReftype>, extractBody: Boolean, extractMethodAndParameterTypeAccesses: Boolean, typeSubstitution: TypeSubstitution?, classTypeArgsIncludingOuterClasses: List<IrTypeArgument>?) =
forceExtractFunction(f, parentId, extractBody = false, extractMethodAndParameterTypeAccesses, typeSubstitution, classTypeArgsIncludingOuterClasses).also { functionId ->
tw.writeCompiler_generated(functionId, CompilerGeneratedKinds.INTERFACE_FORWARDER.kind)
if (extractBody) {
val realFunctionLocId = tw.getLocation(f)
val inheritedDefaultFunction = f.realOverrideTarget
val defaultDefiningInterfaceType = (inheritedDefaultFunction.parentClassOrNull ?: return functionId).typeWith()
extractExpressionBody(functionId, realFunctionLocId).also { returnId ->
extractRawMethodAccess(
f,
realFunctionLocId,
f.returnType,
functionId,
returnId,
0,
returnId,
f.valueParameters.size,
{ argParentId, idxOffset ->
f.valueParameters.mapIndexed { idx, param ->
val syntheticParamId = useValueParameter(param, functionId)
extractVariableAccess(syntheticParamId, param.type, realFunctionLocId, argParentId, idxOffset + idx, functionId, returnId)
}
},
f.dispatchReceiverParameter?.type,
{ callId ->
extractSuperAccess(defaultDefiningInterfaceType, functionId, callId, -1, returnId, realFunctionLocId)
},
null
)
}
}
}
private fun extractFunction(f: IrFunction, parentId: Label<out DbReftype>, extractBody: Boolean, extractMethodAndParameterTypeAccesses: Boolean, typeSubstitution: TypeSubstitution?, classTypeArgsIncludingOuterClasses: List<IrTypeArgument>?) =
if (isFake(f))
null
else {
if (isFake(f)) {
if (needsInterfaceForwarder(f))
makeInterfaceForwarder(f, parentId, extractBody, extractMethodAndParameterTypeAccesses, typeSubstitution, classTypeArgsIncludingOuterClasses)
else
null
} else {
forceExtractFunction(f, parentId, extractBody, extractMethodAndParameterTypeAccesses, typeSubstitution, classTypeArgsIncludingOuterClasses).also {
// The defaults-forwarder function is a static utility, not a member, so we only need to extract this for the unspecialised instance of this class.
if (classTypeArgsIncludingOuterClasses.isNullOrEmpty())
@@ -1202,7 +1249,9 @@ open class KotlinFileExtractor(
private fun extractProperty(p: IrProperty, parentId: Label<out DbReftype>, extractBackingField: Boolean, extractFunctionBodies: Boolean, extractPrivateMembers: Boolean, typeSubstitution: TypeSubstitution?, classTypeArgsIncludingOuterClasses: List<IrTypeArgument>?) {
with("property", p) {
if (isFake(p)) return
fun needsInterfaceForwarderQ(f: IrFunction?) = f?.let { needsInterfaceForwarder(f) } ?: false
if (isFake(p) && !needsInterfaceForwarderQ(p.getter) && !needsInterfaceForwarderQ(p.setter)) return
DeclarationStackAdjuster(p).use {
@@ -5373,6 +5422,7 @@ open class KotlinFileExtractor(
DELEGATED_PROPERTY_SETTER(7),
JVMSTATIC_PROXY_METHOD(8),
JVMOVERLOADS_METHOD(9),
DEFAULT_ARGUMENTS_METHOD(10)
DEFAULT_ARGUMENTS_METHOD(10),
INTERFACE_FORWARDER(11),
}
}