[changelog] Tweak script

script/changelog

@@ -5,17 +5,16 @@
 # Show changes to runtime files between HEAD and previous release tag.
 set -e
 
-head="${1:-HEAD}"
+current_tag="${GITHUB_REF#refs/tags/}"
+start_ref="HEAD"
 
-for sha in `git rev-list -n 100 --first-parent "$head"^`; do
-  previous_tag="$(git tag -l --points-at "$sha" 'v*' 2>/dev/null || true)"
-  [ -z "$previous_tag" ] || break
+# Find the previous release on the same branch, skipping prereleases if the
+# current tag is a full release
+previous_tag=""
+while [[ -z $previous_tag || ( $previous_tag == *-* && $current_tag != *-* ) ]]; do
+  previous_tag="$(git describe --tags "$start_ref"^ --abbrev=0)"
+  start_ref="$previous_tag"
 done
 
-if [ -z "$previous_tag" ]; then
-  echo "Couldn't detect previous version tag" >&2
-  exit 1
-fi
-
-git log --no-merges --format='%C(auto,green)* %s%C(auto,reset)%n%w(0,2,2)%+b' \
-  --reverse "${previous_tag}..${head}" -- `script/build files` etc share
+git log --first-parent --format='%C(auto,green)* %s%C(auto,reset)%n%w(0,2,2)%+b' \
+  --reverse "${previous_tag}.." -- `script/build files` etc share

script/tag-release

@@ -15,7 +15,7 @@ git commit -m "hub $version" -- "$version_file"
 notes_file="$(mktemp)"
 { echo "hub $version"
   echo
-  script/changelog
+  GITHUB_REF="refs/tags/v$version" script/changelog
 } >"$notes_file"
 trap "rm -f '$notes_file'" EXIT