ArrayIndexOutOfBoundsException raised with --target_pattern_file

[ghost]

Description of the bug:

If the file given in the --target_pattern_file option contains an empty comment line, the command bazel build crashes with this exception below:

$ hexdump -C targets.list
00000000  23 0a                                             |#.|
00000002

$ bazel build --target_pattern_file=targets.list
...
FATAL: bazel crashed due to an internal error. Printing stack trace:
java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
	at com.google.devtools.build.lib.runtime.commands.TargetPatternsHelper.lambda$readFrom$0(TargetPatternsHelper.java:61)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(Unknown Source)
	at java.base/java.util.Collections$2.tryAdvance(Unknown Source)
	at java.base/java.util.Collections$2.forEachRemaining(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline.collect(Unknown Source)
	at com.google.devtools.build.lib.runtime.commands.TargetPatternsHelper.readFrom(TargetPatternsHelper.java:64)
	at com.google.devtools.build.lib.runtime.commands.BuildCommand.exec(BuildCommand.java:69)
	at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.execExclusively(BlazeCommandDispatcher.java:664)
	at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.exec(BlazeCommandDispatcher.java:244)
	at com.google.devtools.build.lib.server.GrpcServerImpl.executeCommand(GrpcServerImpl.java:573)
	at com.google.devtools.build.lib.server.GrpcServerImpl.lambda$run$1(GrpcServerImpl.java:644)
	at io.grpc.Context$1.run(Context.java:566)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.base/java.lang.Thread.run(Unknown Source)

On the other hand, no problem with single space after the #.

$ hexdump -C targets.list
00000000  23 20 0a                                          |# .|
00000003

$ bazel build --target_pattern_file=targets.list
...
Your request is correct, but requested an empty set of targets. Nothing will be built.
INFO: Found 0 targets...
INFO: Elapsed time: 1.591s, Critical Path: 0.14s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action

Which category does this issue belong to?

No response

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

No response

Which operating system are you running Bazel on?

linux/amd64

What is the output of bazel info release?

release 7.3.1

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

No response

If this is a regression, please try to identify the Bazel commit where the bug was introduced with bazelisk --bisect.

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[haxorz]

Thank you for the very clear bug report. Skimming over the code history, this was probably introduced by #15903. Looks like that code doesn't handle this exact situation.