Attaching a generated file to a GitHub release using Actions

github-actions/attach-generated-file-to-release.md

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+# Attaching a generated file to a GitHub release using Actions
+
+For [Datasette Desktop](https://github.com/simonw/datasette-app) I wanted to run an action which, when I created a release, would build an asset for that release and then upload and attach it.
+
+I triggered my action on the creation of a new release, like so:
+
+```yaml
+on:
+  release:
+    types: [created]
+```
+
+Assuming previous steps that create a file called `app.zip` in the root of the checkout, here's the final action step which worked for me:
+
+```yaml
+      - name: Upload release attachment
+        uses: actions/github-script@v4
+        with:
+          script: |
+            const fs = require('fs');
+            const tag = context.ref.replace("refs/tags/", "");
+            // Get release for this tag
+            const release = await github.repos.getReleaseByTag({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              tag
+            });
+            // Upload the release asset
+            await github.repos.uploadReleaseAsset({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              release_id: release.data.id,
+              name: "app.zip",
+              data: await fs.readFileSync("app.zip")
+            });
+```
+It uses [actions/github-script](https://github.com/actions/github-script) which provides a pre-configured [octokit/rest.js](https://octokit.github.io/rest.js/) client object.
+
+The `uploadReleaseAsset()` method needs the `owner`, `repo`, `release_id`, `name` (filename) and the file data.
+
+These are mostly available, with the exception of `release_id`. That can be derived for the current release based on the `context.ref` value - strip that down to just the tag, then use `getReleaseByTag()` to get a release object. `release.data.id` will then be the numeric release ID.
+
+My full workflow is at https://github.com/simonw/datasette-app/blob/0.1.0/.github/workflows/release.yml