Option -L is not documented in the "diff --help" output (and
as a consequence, in the generated diff.1 man page either).

The doc/diffutils.info file contains

'-L LABEL'
'--label=LABEL'
     Use LABEL instead of the file name in the context format (*note
     Context Format::) and unified format (*note Unified Format::)
     headers.  *Note RCS::.

so "    --label LABEL" should just be changed to "-L, --label LABEL"
in src/diff.c. Patch attached.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)