Merge 2.10.x to master #84
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`gen.mkZero(NothingTpe)` gives the tree `Predef.???`. Instead, we should leave the `await` field uninitialized with `ValDef(..., rhs = EmptyTree)`. Fixes scala#66
Fix possibly-exponential runtime for DFS graph searches. Improve DFA fixpoint algorithm to correctly compute worklist of only changed nodes for each iteration. Added test that takes > 2 minutes to compile without these improvements.
Avoid NotImplementedError awaiting a Future[Nothing]
If we start with:
async({
val res = await[S[_$1 with String]](s);
if (true)
await[Int](0)
res
})
Typechecking the application (before macro expansion) yields
(where the trees are printed in the form `expr{tpe}`):
async[S[_$1#5738 with String#137]]({
val res: S[_$1#5490 with String] forSome { type _$1#5490 } =
await[S[_$1#5487 with String]](
s{S[_$1#5487 with String]}
){S[_$1#5487 with String]};
if (true)
await(0)
else
()
res{S[_$1#5738 with String]}
}{S[_$1#5738 with String]}){S[_$1#5738 with String]}
Note that the type of the second last line contains a skolemized
symbol `_$1#5738` of the existential `_$1#5490`. This is created
by this case in `Typer#adapt`:
case et @ ExistentialType(_, _) if ((mode & (EXPRmode | LHSmode)) == EXPRmode) =>
adapt(tree setType et.skolemizeExistential(context.owner, tree), mode, pt, original)
Our ANF rewrites part of this code to:
<synthetic> val await$1: S[_$1#5487 with String] = await[S[_$1#5487 with String]](awaitable$1);
val res: S[_$1#5490 with String] forSome { type _$1 } = await$1;
And later, the state machine transformation splits the last line into
a blank field and an assignment. Typechecking the `Assign` node
led to the an type error.
This commit manually attributes the types to the `Assign` node so
as to avoid these problem.
It also reigns in an overeager rewriting of `If` nodes in the
ANF transform, which was due to a bug in the label detection
logic introduced in 4fc5463.
Thanks to @gnovark for yet another devilish test case and
analysis of the problem with label detection.
I worked on a more principled fix on:
https://github.com/retronym/async/compare/ticket/79-2?expand=1
in which I try to use `repackExistential` to convert skolemized
types to existentials for use as the types of synthetic vals
introduced by the ANF transform. This ran into a deeper problem
with existential subtyping in the compiler itself though.
Fix asymptotic performance issues in live variables analysis.
Fix regression around type skolems and if exprs.
…ter-20140721 Conflicts: src/main/scala/scala/async/internal/AsyncTransform.scala src/main/scala/scala/async/internal/Lifter.scala
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