feat(ci): add flatpak to CI

.github/workflows/linux-flatpak-comment.yml

@@ -0,0 +1,92 @@
+# SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+name: Linux Flatpak Comment
+on:
+  workflow_run:
+    workflows: ["Linux Flatpak Package"]
+    types: [completed]
+
+jobs:
+  comment-flatpak:
+    name: Create a comment with a link to the built Flatpak
+    runs-on: ubuntu-latest
+    if: |-
+      github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.conclusion == 'success'
+    steps:
+      - name: Comment Flatpak
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            // Discover the origin pull request ID.
+            // Since GitHub does not include any pull requests from forks as part of a WorkflowRun we need to look up the PR ourselves.
+            const pullRequestsForThisBranch = await github.rest.repos.listPullRequestsAssociatedWithCommit({
+              owner: context.payload.workflow_run.head_repository.owner.login,
+              repo: context.payload.workflow_run.head_repository.name,
+              commit_sha: context.payload.workflow_run.head_branch,
+            });
+            const latestPullRequest = pullRequestsForThisBranch.data.sort((a, b) => b.id - a.id)[0];
+            if (!latestPullRequest) {
+              console.log("Could not find recent pull request related to this workflow run");
+              return;
+            };
+            const prId = latestPullRequest.number;
+            console.log(`Discovered pull request #${prId}`);
+
+            const workflowArtifacts = await github.rest.actions.listWorkflowRunArtifacts({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              run_id: context.payload.workflow_run.id,
+            });
+            const artifact = workflowArtifacts.data.artifacts.filter((artifact) => artifact.name == "com.nextcloud.desktopclient.nextcloud.flatpak")[0];
+
+            if (!artifact) {
+              console.log("Could not find matching artifact");
+              return;
+            }
+
+            // artifact.url and artifact.archive_download_url contain a URL that's supposed to be used by API clients only
+            const artifactUrl = `https://github.com/nextcloud/desktop/actions/runs/${artifact.workflow_run.id}/artifacts/${artifact.id}`;
+
+            const comment_identifier_string = "<!-- automated comment for a flatpak build -->";
+
+            const comment_body = `
+              ${comment_identifier_string}
+
+              Artifact containing the Flatpak bundle: [${artifact.name}.zip](${artifactUrl})
+
+              Digest: \`${artifact.digest}\`
+
+              To test this change/fix you can download the above artifact file, unzip it, and install the bundle with:
+              \`flatpak install --user ${artifact.name}\`
+
+              Please make sure to quit your existing Nextcloud app and backup your data.
+            `;
+
+            console.log("fetching old comments")
+            const comments = await github.rest.issues.listComments({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: prId,
+            });
+
+            comments
+              .data
+              .filter(comment => comment.body?.includes(comment_identifier_string))
+              .forEach(comment => {
+                console.log(`deleting previous Flatpak comment with ID ${comment.id}`)
+                github.rest.issues.deleteComment({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  comment_id: comment.id,
+                })
+              });
+
+            console.log("creating new comment")
+            github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: prId,
+              body: comment_body,
+            });

.github/workflows/linux-flatpak.yml

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+# SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+name: Linux Flatpak Package
+on:
+  pull_request:
+    types: [opened, reopened, synchronize, ready_for_review, closed]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  flatpak:
+    if: ${{ github.event.action != 'closed' && !github.event.pull_request.draft }}
+    name: Linux Flatpak Package
+    runs-on: ubuntu-latest
+    container:
+      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-48
+      options: --privileged
+    steps:
+    - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+    - uses: flatpak/flatpak-github-actions/flatpak-builder@79327416609af08178ad73b352877e51450790b3 # v6.8
+      with:
+        bundle: com.nextcloud.desktopclient.nextcloud.flatpak
+        manifest-path: admin/linux/flatpak/com.nextcloud.desktopclient.nextcloud.yml
+        upload-artifact: true
+        artifact-name: com.nextcloud.desktopclient.nextcloud.flatpak
+        build-bundle: true