Error when running Ninja file

[ndmitchell]

Given:

ninja_required_version = 1.5
build test : phony a b
rule CUSTOM_COMMAND
   command = $COMMAND
build a b : CUSTOM_COMMAND
  COMMAND = cd

It fails with:

# cd (for a b)
shake: Error when running Shake build system:
* b
Prelude.!!: index too large

Reported by Lukas Mosimann at https://groups.google.com/d/msg/shake-build-system/435NOk6hZzc/P3LcADLnBQAJ

[ndmitchell]

The problem is that Ninja rules don't have to create their contents - so even though build a b says it creates a and b, it actually doesn't. Shake on the other hand demands that files are created. There is a flag for Shake to have Ninja compatible behaviour, but I had messed it up in relation to multi-file rules. Now fixed.