ENGDOCS-2409 (#21963)

<!--Delete sections as needed -->

## Description

Spec updates:

Adds compose-spec/compose-spec#563
Adds compose-spec/compose-spec#558
Adds compose-spec/compose-spec#565

## Related issues or tickets

<!-- Related issues, pull requests, or Jira tickets -->

## Reviews

<!-- Notes for reviewers here -->
<!-- List applicable reviews (optionally @tag reviewers) -->

- [ ] Technical review
- [ ] Editorial review
- [ ] Product review

content/reference/compose-file/build.md

@@ -118,6 +118,28 @@ the unused contexts.
 Illustrative examples of how this is used in Buildx can be found
 [here](https://github.com/docker/buildx/blob/master/docs/reference/buildx_build.md#-additional-build-contexts---build-context).
 
+`additional_contexts` can also refer to an image built by another service.
+This allows a service image to be built using another service image as a base image, and to share
+layers between service images.
+
+```yaml
+services:
+ base:
+  build:
+    context: .
+    dockerfile_inline: |
+      FROM alpine
+      RUN ...
+ base:
+  build:
+    context: .
+    dockerfile_inline: |
+      FROM base # image built for service base
+      RUN ...
+    additional_contexts:
+      base: service:base
+```
+
 ### `args`
 
 `args` define build arguments, that is Dockerfile `ARG` values.

content/reference/compose-file/merge.md

@@ -107,8 +107,8 @@ While these types are modeled in a Compose file as a sequence, they have special
 | Attribute   | Unique key               |
 |-------------|--------------------------|
 | volumes     |  target                  |
-| secrets     |  source                  |
-| configs     |  source                  |
+| secrets     |  target                  |
+| configs     |  target                  |
 | ports       |  {ip, target, published, protocol}   |
 
 When merging Compose files, Compose appends new entries that do not violate a uniqueness constraint and merge entries that share a unique key.

content/reference/compose-file/services.md

@@ -1005,6 +1005,29 @@ configuration, which means for Linux `/etc/hosts` get extra lines:
 ::1             myhostv6
 ```
 
+### `gpus`
+
+{{< summary-bar feature_name="Compose gpus" >}}
+
+`gpus` specifies GPU devices to be allocated for container usage. This is equivalent to a [device request](deploy.md#devices) with
+an implicit `gpu` capability.
+
+```yaml
+services:
+  model:
+    gpus: 
+      - driver: 3dfx
+        count: 2
+```
+
+`gpus` also can be set as string `all` to allocate all available GPU devices to the container.
+
+```yaml
+services:
+  model:
+    gpus: all
+```
+
 ### `group_add`
 
 `group_add` specifies additional groups, by name or number, which the user inside the container must be a member of.

data/summary.yaml

@@ -81,6 +81,8 @@ Compose file watch:
   requires: Docker Compose [2.22.0](/manuals/compose/releases/release-notes.md#2220) and later
 Compose format:
   requires: Docker Compose [2.30.0](/manuals/compose/releases/release-notes.md#2300) and later
+Compose gpus:
+  requires: Docker Compose [2.30.0](/manuals/compose/releases/release-notes.md#2300) and later
 Compose include:
   requires: Docker Compose [2.20.3](/manuals/compose/releases/release-notes.md#2203) and later
 Compose label file: