+1 would be used by me

+1 but someone needs to figure out if we need to change jruby-launcher gen for this and I am too busy with upcoming travel. Can someone run -Xtrace log.txt with this applied and make sure the last command passes these new syntaxes through properly?

I've updated jruby-launcher in jruby/jruby-launcher#8.

Is there a reason this is better than piping --properties to grep?

When I go to write a property I start writing -Xtruffle. and then pause as I realise I can't remember the name. So I'd have to erase all that and type --properties | grep truffle. Here as I realise I don't know the name, I just finish off with -Xtruffle... and press enter. I can then edit that line with the property I want as it's all already in place for me to finish.

It's a redundant UI adornment I know, but so is --profile.flat and --profile.

Edit: also, no grep on Windows.

No grep on Windows is the more compelling reason :-)

If nobody else objects I don't have a problem including this.

Will look at error.

Ignore the failure. It may be valid, but I restarted it to see if it goes away.

I'm going to have to investigate whether there's actually a problem, or if these are just bad specs. The threading specs have been notoriously bad.

Entirely unrelated to your stuff.