use target_commitish to determine how to create tag rather than GITHUB_SHA

src/github.ts

@@ -79,6 +79,12 @@ export interface Releaser {
     repo: string;
     ref: string;
   }) : Promise<any>;
+
+  getRef(params: {
+    owner: string;
+    repo: string;
+    ref: string;
+  }) : Promise<any>;
 }
 
 export class GitHubReleaser implements Releaser {
@@ -168,6 +174,14 @@ export class GitHubReleaser implements Releaser {
   }) : Promise<any> {
     return this.github.rest.git.deleteRef(params);
   }
+
+  getRef(params: {
+    owner: string;
+    repo: string;
+    ref: string;
+  }) : Promise<any> {
+    return this.github.rest.git.getRef(params);
+  }
 }
 
 export const asset = (path: string): ReleaseAsset => {
@@ -328,6 +342,9 @@ export const release = async (
     const make_latest = config.input_make_latest;
 
     if(config.input_update_tag){
+
+      let newCommitSha = await getTargetCommit(target_commitish, releaser, owner, repo);
+
       await releaser.deleteRef({
         owner,
         repo,
@@ -337,10 +354,10 @@ export const release = async (
         owner,
         repo,
         ref: "refs/tags/"+existingRelease.tag_name,
-        sha: config.github_sha
+        sha: newCommitSha
       })
 
-      console.log(`Updated ref/tags/${existingRelease.tag_name} to ${config.github_sha}`);
+      console.log(`Updated ref/tags/${existingRelease.tag_name} to ${newCommitSha}`);
       
       // give github the time to draft the release before updating it
       // Else, I think we would have a race condition with github to update the release
@@ -448,6 +465,23 @@ async function createRelease(
   }
 }
 
+async function getTargetCommit(target_commitish: string, releaser: Releaser, owner: string, repo: string) : Promise<string> {
+  if (target_commitish.length == 40) { // sha1 size
+    return target_commitish;
+  } else {
+    // assume it is a branch
+    let resp = await releaser.getRef({
+      owner: owner,
+      repo: repo,
+      ref: "heads/"+target_commitish,
+    })
+    if (resp.status == 404) {
+      throw new Error(`Branch ${target_commitish} not found`);
+    }
+    return resp.data.object.sha;
+  }
+}
+
 function sleep(ms) {
   return new Promise(resolve => setTimeout(resolve, ms));
 }

src/util.ts

@@ -4,7 +4,6 @@ import { statSync, readFileSync } from "fs";
 export interface Config {
   github_token: string;
   github_ref: string;
-  github_sha: string;
   github_repository: string;
   // user provided
   input_name?: string;
@@ -57,7 +56,6 @@ export const parseConfig = (env: Env): Config => {
   return {
     github_token: env.GITHUB_TOKEN || env.INPUT_TOKEN || "",
     github_ref: env.GITHUB_REF || "",
-    github_sha: env.GITHUB_SHA || "",
     github_repository: env.INPUT_REPOSITORY || env.GITHUB_REPOSITORY || "",
     input_name: env.INPUT_NAME,
     input_tag_name: env.INPUT_TAG_NAME?.trim(),