Description of the problem / feature request:

The docs for --output=location say:

For source files, the location of line 1 of the actual file is printed.

This is what I want, but it is not what happens: instead, what is
printed is the location of a reference to the source file from a BUILD
file. There appears to be no way to actually turn a label for a source
file into that source file’s path on disk.

Feature requests: what underlying problem are you trying to solve with this feature?

N/A

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

$ cd "$(mktemp -d)"
$ >WORKSPACE
$ >BUILD <<EOF cat
> py_binary(
>   name = "main",
>   srcs = ["main.py"],
> )
> EOF
$ >main.py
$ bazel query //:main.py --output=location 2>/dev/null
/tmp/tmp.97B2nY3jsI/BUILD:3:10: source file //:main.py

Not even --output=proto includes the promised information:

$ bazel query //:main.py --output=proto | strings
//:main.py
/tmp/tmp.97B2nY3jsI/BUILD:3:10*

What operating system are you running Bazel on?

gLinux (like Debian)

What's the output of bazel info release?

release 0.28.0

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

N/A

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

N/A

Have you found anything relevant by searching the web?

Nope.

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

Nope.