grep.55cf7b6a.diagnosis.txt

If grep is set to silently skip devices, FIFOs, and sockets (-D skip), then
grep does not search on standard input when no file is provided. When the skip
option is enabled, variables devices is set to SKIP_DEVICES (main.c:1852-1859).
If no file is provided, variable file is NULL and variable desc is set to
STDIN_FILENO (main.c:1217-1218). The code which handles SKIP_DEVICES
(main.c:1246-1255) decides to skip STDIN (which is a special device) even
though it should not (desc == STDIN_FILENO). 

Examples of Correct Fixes: 
1) Do not skip if desc is set to STDIN_FILENO. 
2) Do not skip if file is not set (and thus desc is set to STDIN_FILENO). 

Example of Incorrect Fix: 
Negate the skip condition (Regression because it skips everything that should
not be skipped while indeed not skipping STDIN).