Merge branch 'main' into robherley/migration-docs-typo

docs/MIGRATION.md

@@ -3,6 +3,7 @@
 - [Migration](#migration)
   - [Multiple uploads to the same named Artifact](#multiple-uploads-to-the-same-named-artifact)
   - [Overwriting an Artifact](#overwriting-an-artifact)
+  - [Merging multiple artifacts](#merging-multiple-artifacts)
 
 Several behavioral differences exist between Artifact actions `v3` and below vs `v4`. This document outlines common scenarios in `v3`, and how they would be handled in `v4`.
 
@@ -144,3 +145,64 @@ jobs:
 ```
 
 Note that this will create an _entirely_ new Artifact, with a different ID from the previous.
+
+## Merging multiple artifacts
+
+In `v3`, multiple uploads from multiple jobs could be done to the same Artifact. This would result in a single archive, which could be useful for sending to upstream systems outside of Actions via API or UI downloads.
+
+```yaml
+jobs:
+  upload:
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - name: Create a File
+        run: echo "hello from ${{ matrix.runs-on }}" > file-${{ matrix.runs-on }}.txt
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: all-my-files # NOTE: same artifact name
+          path: file-${{ matrix.runs-on }}.txt
+```
+
+The single `all-my-files` artifact would contain the following:
+
+```
+.
+  ∟ file-ubuntu-latest.txt
+  ∟ file-macos-latest.txt
+  ∟ file-windows-latest.txt
+```
+
+To achieve the same in `v4` you can change it like so:
+
+```diff
+jobs:
+  upload:
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - name: Create a File
+        run: echo "hello from ${{ matrix.runs-on }}" > file-${{ matrix.runs-on }}.txt
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v3
+        with:
+-         name: all-my-files
++         name: my-artifact-${{ matrix.runs-on }}
+          path: file-${{ matrix.runs-on }}.txt
++ merge:
++   runs-on: ubuntu-latest
++   needs: upload
++   steps:
++     - name: Merge Artifacts
++       uses: actions/upload-artifact/merge@v4
++       with:
++         name: all-my-files
++         pattern: my-artifact-*
+```
+
+Note that this will download all artifacts to a temporary directory and reupload them as a single artifact. For more information on inputs and other use cases for `actions/upload-artifact/merge@v4`, see [the action documentation](../merge/README.md).