fedora: Introduce own rpkg macro for changelog

git_dir_changelog is useful in theory, but it requires pairs of
annotated tags, which should be generated by rpkg itself to make any
sense, implying a relatively heavyweight interaction whenever I want
to push a new package version.

Also, the default content of the changelog entries include the full
list of changes, but the Fedora Packaging Guidelines specifically
mention that:

  [t]hey must never simply contain an entire copy of the source
  CHANGELOG entries.

We don't have a CHANGELOG file, but the full git history is
conceptually equivalent for this purpose, I guess.

Introduce our own passt_git_changelog() rpkg macro, building
changelog entries, using tags in the form DATE-SHA, where DATE
is an ISO 8601 date representation, and SHA is a short (7-digits)
form of the head commit at a given moment (git push).

These changelog entries mention, specifically, changes to the
packaging information itself (entries under contrib/fedora), and
simply report a link to cgit for the ranges between tags.

Reported-by: Benson Muite <benson_muite@emailplus.org>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

contrib/fedora/passt.spec

@@ -93,4 +93,4 @@ semodule -r pasta 2>/dev/null || :
 %{_datadir}/selinux/packages/%{name}/pasta.pp
 
 %changelog
-{{{ git_dir_changelog }}}
+{{{ passt_git_changelog }}}

contrib/fedora/rpkg.macros

@@ -14,3 +14,37 @@
 function git_version {
 	printf "0.git.%s.%s" "$(date -u -I | tr - _)" "$(git rev-parse --short HEAD)"
 }
+
+function passt_git_changelog_entry {
+	__from="${2}"
+	__to="${1}"
+
+	[ -z "${__from}" ] && __from="$(git rev-list --max-parents=0 HEAD)"
+
+	__date="$(git log --pretty="format:%cI" "${__to}" -1)"
+	__author="$(git log -1 --pretty="format:%an <%ae>" ${__to} -- contrib/fedora)"
+
+	printf "* %s %s - %s\n" "$(date "+%a %b %e %Y" -d "${__date}")" "${__author}" "0.git.${1}-0"
+
+	IFS='
+'
+	for l in $(git log ${__from}..${__to} --pretty=format:"- %s" -- contrib/fedora); do
+		printf "%s%s\n" '-' "${l#*:}"
+	done
+	unset IFS
+
+	printf "%s Upstream changes: https://passt.top/passt/log/?qt=range&q=%s..%s\n\n" '-' "${__from}" "${__to}"
+}
+
+function passt_git_changelog_pairs {
+	while [ -n "${2}" ]; do
+		passt_git_changelog_entry "${1}" "${2}"
+		shift 2
+	done
+
+	passt_git_changelog_entry "${1}" ""
+}
+
+function passt_git_changelog {
+	passt_git_changelog_pairs $((git tag --sort="-v:refname"|tail -n+2; git tag --sort="-v:refname") | sort -r)
+}