configs: Rawhide to accept GPG key from future Fedora Rawhide+1

Fixes: #1338

mock-core-configs/etc/mock/templates/fedora-rawhide.tpl

@@ -39,7 +39,7 @@ user_agent={{ user_agent }}
 
 {%- macro rawhide_gpg_keys() -%}
 file:///usr/share/distribution-gpg-keys/fedora/RPM-GPG-KEY-fedora-$releasever-primary
-{%- for version in [releasever|int, releasever|int - 1]
+{%- for version in [releasever|int, releasever|int - 1, releasever|int + 1]
 %} file:///usr/share/distribution-gpg-keys/fedora/RPM-GPG-KEY-fedora-{{ version }}-primary
 {%- endfor %}
 {%- endmacro %}

releng/rawhide-branching.sh

@@ -17,6 +17,20 @@ for config in fedora-??-x86_64.cfg; do
     next_version=$(( version + 1 ))
 done
 
+rawhide_plus_one_version=$(( next_version + 1 ))
+next_gpg=/usr/share/distribution-gpg-keys/fedora/RPM-GPG-KEY-fedora-$rawhide_plus_one_version-primary
+test -e "$next_gpg" || {
+    cat >&2 <<EOF
+File $next_gpg not found!
+
+The new Fedora Rawhide ($next_version) requires a GPG key for Fedora $rawhide_plus_one_version,
+which must be generated by Fedora Infrastructure team and shipped in the
+distribution-gpg-keys.rpm package.  This either has not happened yet, the
+package is outdated, or it is not even installed on this box.
+EOF
+    exit 1
+}
+
 architectures=()
 for config in fedora-"$version"-*.cfg; do
     architecture=$(echo "$config" | sed -e "s/fedora-$version-//" -e "s/.cfg//")

releng/release-notes-next/fedora-rawhide-key-plus-one.config

@@ -0,0 +1,4 @@
+Fedora Rawhide configurations, such as releasever=41 now, accept GPG keys from
+Fedora releasever+1 (for example, 42, not yet used for RPM signatures).  This
+change is implemented to address the typically short and unnecessary
+inconvenience during [the Fedora branching process][issue#1338] in the future.