fix: fallback to look at releases when looking for latest release

src/manifest.ts

@@ -487,6 +487,7 @@ export class Manifest {
       let latestRelease = releasesByPath[path];
       if (
         !latestRelease &&
+        this.releasedVersions[path] &&
         this.releasedVersions[path].toString() !== '0.0.0'
       ) {
         const version = this.releasedVersions[path];
@@ -937,11 +938,16 @@ async function latestReleaseVersion(
     `Looking for latest release on branch: ${targetBranch} with prefix: ${prefix}`
   );
 
+  // collect set of recent commit SHAs seen to verify that the release
+  // is in the current branch
+  const commitShas = new Set<string>();
+
   // only look at the last 250 or so commits to find the latest tag - we
   // don't want to scan the entire repository history if this repo has never
   // been released
   const generator = github.mergeCommitIterator(targetBranch, 250);
   for await (const commitWithPullRequest of generator) {
+    commitShas.add(commitWithPullRequest.sha);
     const mergedPullRequest = commitWithPullRequest.pullRequest;
     if (!mergedPullRequest) {
       continue;
@@ -974,7 +980,34 @@ async function latestReleaseVersion(
 
     return version;
   }
-  return;
+
+  // If not found from recent pull requests, look at releases. Iterate
+  // through releases finding valid tags, then cross reference
+  const releaseGenerator = github.releaseIterator();
+  const candidateReleaseVersions: Version[] = [];
+  for await (const release of releaseGenerator) {
+    const tagName = TagName.parse(release.tagName);
+    if (!tagName) {
+      continue;
+    }
+
+    if (tagName.component === prefix) {
+      logger.debug(`found release for ${prefix}`, tagName.version);
+      if (!commitShas.has(release.sha)) {
+        logger.debug(
+          `SHA not found in recent commits to branch ${targetBranch}, skipping`
+        );
+        continue;
+      }
+      candidateReleaseVersions.push(tagName.version);
+    }
+  }
+  logger.debug(
+    `found ${candidateReleaseVersions.length} possible releases.`,
+    candidateReleaseVersions
+  );
+
+  return candidateReleaseVersions.sort((a, b) => a.compare(b))[0];
 }
 
 function mergeReleaserConfig(

src/version.ts

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import * as semver from 'semver';
+
 const VERSION_REGEX =
   /(?<major>\d+)\.(?<minor>\d+)\.(?<patch>\d+)(-(?<preRelease>[^+]+))?(\+(?<build>.*))?/;
 
@@ -49,6 +51,10 @@ export class Version {
     return new Version(major, minor, patch, preRelease, build);
   }
 
+  compare(other: Version): -1 | 0 | 1 {
+    return semver.compare(this.toString(), other.toString());
+  }
+
   toString(): string {
     const preReleasePart = this.preRelease ? `-${this.preRelease}` : '';
     const buildPart = this.build ? `+${this.build}` : '';