Fixes #120 Artifacts can be removed even when new ones aren't provided

src/ArtifactDestroyer.ts

@@ -0,0 +1,20 @@
+import {Releases} from "./Releases";
+import * as core from "@actions/core";
+
+export interface ArtifactDestroyer {
+    destroyArtifacts(releaseId: number): Promise<void>
+}
+
+export class GithubArtifactDestroyer implements ArtifactDestroyer {
+    constructor(private releases: Releases) {
+    }
+
+    async destroyArtifacts(releaseId: number): Promise<void> {
+        const releaseAssets = await this.releases.listArtifactsForRelease(releaseId)
+        for (const artifact of releaseAssets) {
+            const asset = artifact
+            core.debug(`Deleting existing artifact ${artifact.name}...`)
+            await this.releases.deleteArtifact(asset.id)
+        }
+    }
+}