All reports of debian-rules-should-not-use-underscore-variable for the archive. The extended description of this tag is:
The rules file use the make variable $(_).
According to Policy 4.9, 'invoking either of make -f debian/rules <...> or ./debian/rules <args...>' must result in identical behavior'. One way to inadvertently violate this policy is to use the $_ variable.
If the rules file uses $(dir $(_)) to discover the directory containing the source package (presumably in order to implement the get-orig-source target), please replace it by $(dir $(firstword $(MAKEFILE_LIST))).
Refer to Debian Policy Manual section 4.9 (Main building script:
debian/rules) for details.
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