Fix returns from within finalizers

When a return in a finalizer was reached through a return within the try
block, the backend ignored the return in the finalizer:

    try {
      try { return 1 }
      finally { return 2 }
    } finally { println() }

This expression should evaluate to 2 (it does in 2.11.8), but in 2.12.0
it the result is 1.

The Scala spec is currently incomplete, it does not say that a finalizer
should be exectuted if a return occurs within a try block, and it does
not specify what happens if also the finally block has a return.

So we follow the Java spec, which basically says: if the finally blocks
completes abruptly for reason S, then the entire try statement completes
abruptly with reason S. An abrupt termination of the try block for a
different reason R is discarded.

Abrupt completion is basically returning or throwing.

3 files changed, 4 insertions, 13 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala b/src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala
index 0b07e12917..b0815b0008 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala
@@ -488,16 +488,11 @@ abstract class BCodeBodyBuilder extends BCodeSkelBuilder {
           bc emitRETURN returnType
         case nextCleanup :: rest =>
           if (saveReturnValue) {
-            if (insideCleanupBlock) {
-              reporter.warning(r.pos, "Return statement found in finally-clause, discarding its return-value in favor of that of a more deeply nested return.")
-              bc drop returnType
-            } else {
-              // regarding return value, the protocol is: in place of a `return-stmt`, a sequence of `adapt, store, jump` are inserted.
-              if (earlyReturnVar == null) {
-                earlyReturnVar = locals.makeLocal(returnType, "earlyReturnVar")
-              }
-              locals.store(earlyReturnVar)
+            // regarding return value, the protocol is: in place of a `return-stmt`, a sequence of `adapt, store, jump` are inserted.
+            if (earlyReturnVar == null) {
+              earlyReturnVar = locals.makeLocal(returnType, "earlyReturnVar")
             }
+            locals.store(earlyReturnVar)
           }
           bc goTo nextCleanup
           shouldEmitCleanup = true
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
index dbad37cd5b..fdb5687311 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala
@@ -255,7 +255,6 @@ abstract class BCodeSkelBuilder extends BCodeHelpers {
     // used by genLoadTry() and genSynchronized()
     var earlyReturnVar: Symbol     = null
     var shouldEmitCleanup          = false
-    var insideCleanupBlock         = false
     // line numbers
     var lastEmittedLineNr          = -1
 
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSyncAndTry.scala b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSyncAndTry.scala
index 9d4ef44546..add2c5ffe6 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BCodeSyncAndTry.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BCodeSyncAndTry.scala
@@ -348,13 +348,10 @@ abstract class BCodeSyncAndTry extends BCodeBodyBuilder {
       // `shouldEmitCleanup` can be set, and at the same time this try expression may lack a finally-clause.
       // In other words, all combinations of (hasFinally, shouldEmitCleanup) are valid.
       if (hasFinally && currentFinallyBlockNeedsCleanup) {
-        val savedInsideCleanup = insideCleanupBlock
-        insideCleanupBlock = true
         markProgramPoint(finCleanup)
         // regarding return value, the protocol is: in place of a `return-stmt`, a sequence of `adapt, store, jump` are inserted.
         emitFinalizer(finalizer, null, isDuplicate = true)
         pendingCleanups()
-        insideCleanupBlock = savedInsideCleanup
       }
 
       /* ------ (4) finally-clause-for-normal-nonEarlyReturn-exit