Update scala modules sbt plugin to 1.0.3 #1
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Java support serialization of lambdas by using the serialization proxy pattern. Deserialization of a lambda uses `LambdaMetafactory` to create a new anonymous subclass. More details of the scheme are documented: https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/SerializedLambda.html From those docs: > SerializedLambda has a readResolve method that looks for a > (possibly private) static method called $deserializeLambda$ > in the capturing class, invokes that with itself as the first > argument, and returns the result. Lambda classes implementing > $deserializeLambda$ are responsible for validating that the > properties of the SerializedLambda are consistent with a lambda > actually captured by that class. The Java compiler generates code in `$deserializeLambda$` that switches on the implementation method name and signature to locate an invokedynamic instruction generated for the particular lambda expression. Then, the `SerializedLambda` is further unpacked, validating that this implementation method still represents the same functional interface as it did when it was serialized. (The source may have been recompiled in the interim.) In Java, serializable lambda expressions are the exception rather than the rule. In Scala, however, the serializability of `FunctionN` means that we would end up generating a large amount of code to support deserialization. Instead, we are pursuing an alternative approach in which the `$deserializeLambda$` method is a simple forwarder to the generic deserializer added here. This is capable of deserializing lambdas created by the Java compiler, although this is not its intended use case. The enclosed tests use Java lambdas. This generic deserializer also works by calling `LambdaMetafactory`, but it does so explicitly, rather than implicitly during linkage of the `invokedynamic` instruction. We have to mimic the caching property of `invokedynamic` instruction to ensure we reuse the classes when constructing. The cache here uses weak references to keys and values to avoid retention of `Class` or `ClassLoader` instances. If the name or signature of the implementation method has changed, we fail during deserialization with an `IllegalArgumentError.` However, we do not fail fast in a few cases that Java would, as we cannot reflect on the "current" functional interface supported by this implementation method. We just instantiate using the "previous" functional interface class/method. This might: 1. fail inside `LambdaMetafactory` if the new implementation method is not compatible with the old functional interface. 2. pass through `LambdaMetafactory` by chance, but fail when instantiating the class in other cases. For example: ``` % tail sandbox/test{1,2}.scala ==> sandbox/test1.scala <== class C { def test: (String => String) = { val s: String = "" (t) => s + t } } ==> sandbox/test2.scala <== class C { def test: (String, String) => String = { (s, t) => s + t } } % (for i in 1 2; do scalac -Ydelambdafy:method -Xprint:delambdafy sandbox/test$i.scala 2>&1 ; done) | grep 'def $anon' final <static> <artifact> private[this] def $anonfun$1(t: String, s$1: String): String = s$1.+(t); final <static> <artifact> private[this] def $anonfun$1(s: String, t: String): String = s.+(t); ``` 3. Silently create an instance of the old functional interface. For example, imagine switching from `FuncInterface1` to `FuncInterface2` where these were identical other than the name. I don't believe that these are showstoppers.
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