better patching documentation

When many projects are processed and patched (like in a multi-module build with hundreds of modules), applying the patches is not straight-forward.

The one option is to setup the plugin with <arg>-Xplugin:ErrorProne -XepAllErrorsAsWarnings -XepPatchChecks:DefaultCharset -XepPatchLocation:${project.build.directory}</arg>

create a script

#/tmp/patchit
cd "$(dirname $1)/.."
patch -p1 -u -i target/error-prone.patch

and run

mvn verify -Perrorprone --threads=8
find . -iname error-prone.patch | xargs -I % -P 1 /tmp/patchit %

i couldn’t get patch -d option working, and note how I have to xargs -P 1

The other option is to create the patch file first as an append only file, and then build, apply, remove:

touch error-prone.patch
sudo chattr +a error-prone.patch
mvn verify -Perrorprone --threads=1
patch -p0 -u -i error-prone.patch
sudo chattr -a error-prone.patch
rm error-prone.patch

I suggestion one or both of the following:

• add an “append to patch file” option to avoid the chattr stuff
• add an option to apply the patch directly on the source files as with git this simply shows up as changes to the working tree and can be applied/rejected

[delanym]

@Stephan202 thanks, by the logs it looks like it works, but now I cant get any patches to apply https://github.com/google/error-prone/issues/3349

[Stephan202]

@delanym that could be implemented using a flag. But I’m not an Error Prone maintainer, so I’m not sure such a PR would be accepted. Let’s see whether any of the maintainers replies. 👀