from man:
  --srpm                operate on corresponding source RPM

From this I would assume that it is alias for `--arch=src --enablerepo='*-source'`.

However, it doesn't work:

[brain@x1carbon pitivi]$ sudo dnf repoquery --enablerepo=rawhide-source --arch=src --whatrequires meson
Last metadata expiration check: 0:00:00 ago on Tue Dec 13 09:51:04 2016 CET.
angelscript-0:2.31.1-3.fc26.src
gst-transcoder-0:1.8.2-1.fc26.src
gstreamer1-plugin-mpg123-0:1.10.0-3.fc26.src
pitivi-0:0.97.1-5.fc26.src
[brain@x1carbon pitivi]$ 

[brain@x1carbon pitivi]$ sudo dnf repoquery --srpm --whatrequires meson
enabling rpmfusion-nonfree-rawhide-source repository
enabling rpmfusion-free-rawhide-source repository
enabling rawhide-source repository
Last metadata expiration check: 0:00:23 ago on Tue Dec 13 09:51:04 2016 CET.
[brain@x1carbon pitivi]$