static-promotion: pretty printer error

[anshumanmohan]

There seems to be a small bug in the pretty printer.

In this commit I have pushed two files. a.futil and b.futil. The former was generated via the eDSL and the latter by running

cargo run -- a.futil -p static-promotion -m file > b.futil

The file b.futil has a stray closing paren here.

[sampsyo]

Super weird thing!!

I was able to reduce the test case. Here's a file that triggers the problem on a round-trip through the pretty printer:

static<1> component stats() -> () {
  cells {}
  wires {}
  control {}
}

component main() -> () {
  cells {
    stats = stats();
  }
  wires {}
  control {
    seq {
      static<1> invoke stats()();
    }
  }
}

To see the problem, run:

cargo run -- -d all that_futil.futil

You will see these offending lines:

      static<1> invoke stats()()
      );

Anyway, the problem seems to come from having a static invoke inside a seq... nothing more than that appears to be required.

---

If you're curious, most of the reduction work was done by Shrink Ray. Here was the original interesting test I used most of the time:

#!/bin/sh -x
set -e

CALYX=/Users/fabian/cu/research/futil/target/debug/calyx

# Check that the original program parses.
$CALYX -d all $1 > /dev/null

# Apply a pass and re-parse.
outfile="$1-compiled"
$CALYX -p static-promotion -m file $1 > $outfile

# Abort here (it's uninteresting) when parsing this file *succeeds*.
! $CALYX -d all $outfile > /dev/null 2> err.txt

# This is interesting if we find the error we're looking for.
grep 'expected identifier' err.txt

This test follows @anshumanmohan's advice directly (check that the original file parses, but passing it through the static-promotion pass and pretty-printing produces an invalid file). Shrink Ray left me with a big control nest and wasn't quite capable of deleting (for example) an entire if foo { ... } wrapper while preserving the body, so I helped it out from there. I then noticed that we could probably get the same effect by manually doing the promotion (writing static<1> in front of the target component and the invoke), so I changed the interestingness test to just look for stuff that failed two pretty-printing round-trips, which got us here.

Along the way, Shrink Ray discovered a fascinating fact I didn't know about our parser: it doesn't require whitespace between keywords and lots of stuff! For example, this file parses:

componentstats() -> () {
  cells {}
  wires {}
  control {}
}

componentmain() -> () {
  cells {
    stats = stats();
  }
  wires {}
  control {
    seq {
      invokestats()();
    }
  }
}

Tired of typing the space in component main? No problem! Calyx will parse componentmain just fine.