Misleading error message when glob expands to empty list of files

[ittaiz]

I moved a test target from the root of my project to a sub package and forgot to update the glob expression of my sources (was glob(["src/test/java/com/example/*.java"]) and should have been changed to glob(["*.java"]) after the move).

When I ran the build I got an error message which IMHO is somewhat misleading.
The error message says that deps is not allowed without srcs and suggests to move them to runtime_deps. Only after a bit of digging I realized that the glob expanded to an empty list and so Bazel thinks I did not declare any sources. Problem is that when you "statically" look at the target you see that srcs is defined.

ERROR: /Users/ittaiz/workspace/bazel-playground/java-getting-started/src/test/java/com/example/BUILD:5:12: in deps attribute of java_test rule //src/test/java/com/example:hola: deps not allowed without srcs; move to runtime_deps?

WDYT about adding to the error message something which says that maybe the srcs is defined but is actually empty?

[kchodorow]

Good idea.

[ittaiz]

If you want a PR I'd be happy to give it a try given a pointer to the relevant place.
In any case this isn't in a hurry for me.

[kchodorow]

Thanks! Should just be adding another isExplicitlySpecified to https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/rules/java/JavaCommon.java#L567.

[ittaiz]

So you're talking about changing the implementation and not the error message, right?
replace
&& ruleContext.attributes().get("srcs", BuildType.LABEL_LIST).isEmpty()
with
&& !ruleContext.getRule().isAttributeValueExplicitlySpecified("srcs")?

[kchodorow]

I think you'd need to add the && !ruleContext.getRule().isAttributeValueExplicitlySpecified("srcs") clause, you still need the isEmpty() check. I haven't tested it or anything, though.

[ittaiz]

ok, will handle it from here.
Thanks!

[laurentlb]

This will change with #8195

In the future, the glob function will fail if the pattern doesn't match anything. This will help you find the bug quickly in this case (the attribute allow_empty lets you opt in the old behavior).