$(execpath :filegroup) and $(rootpath :filegroup) give incorrect error messages

[bcsgh]

Description of the problem / feature request:

using $(execpath :filegroup) and $(rootpath :filegroup) where :filegroup expands to more than one file correctly give an error, but the error text is incorrect in that is says

label '//:filegroup' in $(location) expression expands to more than one file, please use $(locations //:filegroup)

where as it should mention e.g. execpath and execpaths.

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

This error message should be updated.

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

filegroup(
  name = "filegroup",
  srcs = ["a", "b"],
)
genrule(
  name = "bogo",
  tools = [":filegroup"],
  cmd = "echo $(execpath :filegroup) $(rootpath :filegroup)"
  outs = ["X"],
)

What operating system are you running Bazel on?

Linux 20.04

What's the output of bazel info release?

$ bazel info release
release 4.0.0