Add shell scripts for use with cargo-bisect-rustc

[chrissimpkins]

This PR adds three shell scripts in a new scripts directory. They support the following during bisections with this tool:

• deicer.sh - automate ICE identification during bisection with cargo build, returns exit status code 1 when the stderr substring "error: internal compiler error" is identified and ignores all other non-zero exit status code build fails (script workaround for Flag to check for internal compiler errors #34). "regression" = ICE (only)
• find.sh - stdout/err stream substring search, returns exit status code 1 when stdout/err substring is identified. "regression" = identified substring in stdout/err stream.
• findfix.sh - reverses the logic of the cargo build exit status to locate fixes - when build exits with 1, script exits with 0 and when build exits with 0, script exits with 1 (script workaround for feature request: Invert status #28 as recommended by kennytm). "regression" = fix

If these are appropriate upstream, I'd be happy to add documentation in the tutorial or README.

[hellow554]

I would suggest to change this to use parameter expansion and let the variable set from the outer world, so this script would be more generic and you can do stuff like:

env NEEDLE="E0600" scripts/find.sh

instead of manually changing the script.

So something like:

! cargo build 2>&1 | grep "${NEEDLE:-E0642}"

should do the trick

[chrissimpkins]

Great idea! Thoughts about using a regex for any compiler error code as the default? Is that a common enough task or is there a better generally useful default fallback when env var is not set?

[chrissimpkins]

Holding on edits until #47 (comment) is settled.

[chrissimpkins]

The discussion about this PR forked into a few different threads... :)

https://rust-lang.zulipchat.com/#narrow/stream/217417-t-compiler.2Fcargo-bisect-rustc/topic/Scripts.20for.20use.20with.20cargo-bisect-rustc

#34 (comment)

My understanding of the consensus is that the ideal approach is through implementation in the Rust source rather than through external scripts. I think that we all agree on this point.

It sounds like @pnkfelix plans to tackle the changes in the tool. I'd be happy to pitch in on the effort if there is anything that I can do.

[pnkfelix]

@chrissimpkins FYI I finally posted my PR for ICE support (and more) in PR #53

[chrissimpkins]

@pnkfelix ty!