old_contents: """Execute a binary.
  
  The example below executes the binary target "//actions_run:merge" with
  some arguments. The binary will be automatically built by Bazel.
  
  The rule must declare its dependencies. To do that, we pass the target to
  the attribute "_merge_tool". Since it starts with an underscore, it is private
  and users cannot redefine it.
  """
  
  def _impl(ctx):
      # The list of arguments we pass to the script.
      args = [ctx.outputs.out.path] + [f.path for f in ctx.files.chunks]
  
      # Action to call the script.
      ctx.actions.run(
          inputs = ctx.files.chunks,
          outputs = [ctx.outputs.out],
          arguments = args,
          progress_message = "Merging into %s" % ctx.outputs.out.short_path,
          executable = ctx.executable.merge_tool,
      )
  
  concat = rule(
      implementation = _impl,
      attrs = {
          "chunks": attr.label_list(allow_files = True),
          "out": attr.output(mandatory = True),
          "merge_tool": attr.label(
              executable = True,
              cfg = "exec",
              allow_files = True,
              default = Label("//actions_run:merge"),
          ),
      },
  )
  
new_contents: """Execute a binary.
  
  The example below executes the binary target "//actions_run:merge" with
  some arguments. The binary will be automatically built by Bazel.
  
  The rule must declare its dependencies. To do that, we pass the target to
  the attribute "merge_tool".
  """
  
  def _impl(ctx):
      # The list of arguments we pass to the script.
      args = [ctx.outputs.out.path] + [f.path for f in ctx.files.chunks]
  
      # Action to call the script.
      ctx.actions.run(
          inputs = ctx.files.chunks,
          outputs = [ctx.outputs.out],
          arguments = args,
          progress_message = "Merging into %s" % ctx.outputs.out.short_path,
          executable = ctx.executable.merge_tool,
      )
  
  concat = rule(
      implementation = _impl,
      attrs = {
          "chunks": attr.label_list(allow_files = True),
          "out": attr.output(mandatory = True),
          "merge_tool": attr.label(
              executable = True,
              cfg = "exec",
              allow_files = True,
              default = Label("//actions_run:merge"),
          ),
      },
  )
  
subject: Update docstring in actions_run example. (#178)