Unexpected character

[utaal]

Hi,

I'm trying this on a somewhat complex project, and I'm occasionally getting the following error message when I run cargo +nightly rerast --rules_file=changes.rs --diff

Unexpected character: R at (1:1)

(The second number in brackets -- maybe a character position -- changes every time I run the command)

[davidlattimore]

Thanks for trying Rerast and sorry it's giving such an unhelpful error message. When you say "occasionally" - does it succeed if you rerun the same command on the same source, or is it consistent until you've edited the source? When it happens, can you confirm that "cargo check" succeeds?

I'm assuming the project is one that you can't share? If that's the case, I might need to do an overhaul of the error reporting to try to get the message to be more helpful. Although I should probably do that anyway. I can't find 'Unexpected character' in either the rerast source, nor the rustc source, so I'm not sure where it's coming from.

[davidlattimore]

Woohoo, I just reproduced this and then was able to figure out what was happening. Rerast calls "cargo check" in order to get the rustc command lines needed in order to build the local targets, when doing this, rerast acts as a wrapper around the compiler and prints out the command line as a JSON string which is then picked up and read by the parent rerast process. However if there are multiple build targets - e.g. if there are integration tests - cargo will run the "compiler" (rerast) multiple times in parallel. The outputs were getting interleaved resulting in corrupted JSON. The fix is simple - add -j 0 to the cargo check command line in order to not run things in parallel. I'll also improve the error reporting if/when we do get JSON parse errors. Fix should be in the next release. Sorry for the delay and thanks again for the report.