Invalid file path pattern on Windows

[ben-manes]

A student trying to run the simulator in Caffeine faced a compilation error because of a malformed regex. I reviewed the Gradle build configuration (build, options) and do not see a mistake there. Since I am not very familiar with Windows my debugging is limited.

I was able to reproduce his problem by running a Windows 10 trial virtual machine. The attached screenshot is from ".\gradlew.bat simulator:run -S". I disabled the errorprone plugin and provided the student those steps so that his project is unblocked.

[ben-manes]

The problem appears to be due to excluding generated source code from the errorprone analysis.

error-prone/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java

Lines 460 to 462 in 22990c1

	} else if (arg.startsWith(EXCLUDED_PATHS_PREFIX)) {
	String pathRegex = arg.substring(EXCLUDED_PATHS_PREFIX.length());
	builder.setExcludedPattern(Pattern.compile(pathRegex));

where my codeQuality.gradle file includes the option,

excludedPaths = "${buildDir}/generated-sources/.*"

From the error this looks like a wrong assumption that the path is UNIX style, so a Windows path separator must be escaped.

[ben-manes]

From the docs, I suppose one could argue that the above is a user error that violates the param as it is described as

Additionally, you can completely exclude certain paths from any Error Prone checking via the -XepExcludedPaths flag. The flag takes as an argument a regular expression that is matched against a source file’s path to determine whether it should be excluded. So, to exclude files in any sub-directory of a path containing build/generated, use the option:

-XepExcludedPaths:.*/build/generated/.*

So while using buildDir is a best-practice in Gradle (as build is merely the default name), it results in an invalid regex. Switching to mirror the example should work. Perhaps better error handling would be helpful?

[Stephan202]

We had a similar report from a Windows user and ended up modifying the regex to clarify that the initial path should be interpreted verbatim:

-XepExcludedPaths:\Q${project.build.directory}${file.separator}\E.*

(We're using Maven, but I imagine this trick will also work with Gradle.)

Perhaps it's worthwhile to document this trick somewhere.

[tbroyer]

Fwiw, in Gradle, using absolute paths make the task non-relocatable, so using a relative path like in the docs would actually be better as it makes your compile task cacheable (and that cache relocatable).
So the best would then probably be to use something like """\Q${rootProject.relativePath(project.buildDir) + File.separator}\Egenerated-sources\Q${File.separator}\E.*""" (this is Kotlin, I don't know Groovy)

[ben-manes]

Thanks @tbroyer and @Stephan202. Those are helpful insights. I followed up by removing the exclusion as it only suppressed a warning due to using the @AutoBuilder extension, which errorprone doesn't expect.

[Stephan202]

We had a similar report from a Windows user and ended up modifying the regex to clarify that the initial path should be interpreted verbatim:

-XepExcludedPaths:\Q${project.build.directory}${file.separator}\E.*

(We're using Maven, but I imagine this trick will also work with Gradle.)

Perhaps it's worthwhile to document this trick somewhere.

So... it turns out that -XepExcludedPaths:\Q${project.build.directory}${file.separator}\E.* doesn't actually work (at least not anymore). What does seem to work is -XepExcludedPaths:(?!.*/src/[^/]+/java/.*).*; see PicnicSupermarket/error-prone-support#927 for details.