Infinite recursion in TailRec

[OlivierBlanvillain]

The TailRec phase goes into an infinit loop when processing a tree: Apply such that tree.symbol != tree.fun. This is the loop I observed with jstack:

• src/dotty/tools/dotc/transform/TailRec.scala#309
• src/dotty/tools/dotc/transform/TailRec.scala#210
• src/dotty/tools/dotc/transform/TailRec.scala#190
• src/dotty/tools/dotc/transform/TailRec.scala#177

Unfortunately I don't see how I could derive a minimized test case from the very large scalatest code base, if someone has an idea on how to pinpoint the issue in source please let me know!

[DarkDimius]

I don't think that making tailrec have less guards would be a proper way to resolve this.
There are several locations in Dotty & Liker where extraction similar to https://github.com/lampepfl/dotty/blob/75f4400/src/dotty/tools/dotc/transform/TailRec.scala#L198-L206 is happening, where symbol equality test is the way to detect when curried function application is entirely deconstructed.

It would be better to find how this irregular Apply node was created in first place. Did you try running with Ycheck enabled?

[OlivierBlanvillain]

Did you try running with Ycheck enabled?

No, so far I could only reproduce this by compiling the entirety of scalatest, and I don't really have an idea on how to reduce the search space...

[DarkDimius]

@OlivierBlanvillain, you should still be able to run under "-Ycheck:firstTransform" and see if Ycheck complains, even before minimization.

[OlivierBlanvillain]

I minimized this issue in #1687. Turns out it was not an infinite recursion but just a very large code explosion which looked infinite thought jstack :)