$(location) should use runtime path when used in jvm_flags attribute

[shahms]

We have a binary which requires the javac.jar be present in its bootclasspath. Prior to bazel 0.4.4, the following invocation worked (but was obviously less than ideal):

jvm_flags = [
    "-Xbootclasspath/p:$$JAVA_RUNFILES/bazel_tools/third_party/java/jdk/langtools/javac.jar",
],

With bazel 0.4.4 the file name specific path has broken, as the actual file name of the target is now javac-9-dev-r3297-1.jar.

Ideally, we'd be able to use $(location @bazel_tools//third_party/java/jdk/langtools:javac_jar), however that expands to external/bazel_tools/third_party/java/jdk/langtools/javac-9-dev-r3297-1.jar which is the build path and not the runtime path for that file. Needless to say, I'd like to avoid hard-coding another path which will break or fragile inline path-munging hacks. It seems like the correct answer is for $(location) to use the runtime path when specified in jvm_flags.

[meteorcloudy]

@damienmg Do you think it's reasonable to support this feature? Or is there a better way to find the runtime path of javac.jar?

[meteorcloudy]

//cc @kchodorow

[damienmg]

FWIW we cannot make $(location ) returns an absolute path but it should be able to return a path relative to the runfile tree. @kchodorow should definitely knows how / when it will be possible to do so.

[kchodorow]

It's an awfully big hammer, but Skylark's short_path gives you the runtime path. We're working on making the runtime path match the build path (for sources, at least), but it's taking a lot longer than planned.

[ittaiz]

Hey, I have this exact same need but I can't use short_path since we're talking about a macro...
It's basically wrapping rules_scala with a macro and computing some values (one of them being the short_path of the output of the rule being wrapped)

[ittaiz]

ping. I need this to be able to work with sandboxing/remote execution...

[hlopko]

Adding a link to a corresponding StackOverflow question.

[ulfjack]

It seems reasonable to change $(location) to output the runtime path for attributes that are clearly only used at runtime. If there are any cases where it's not clear, we could add another function $(rlocation) or $(runtime_location) to return the runtime path.

[ittaiz]

Another function would be great!

[ulfjack]

Do you think that there are a lot of cases where it's unclear?