build: update git url queries behavior

Signed-off-by: CrazyMax <[email protected]>

Author: crazy-max

content/manuals/build/concepts/context.md

@@ -247,10 +247,9 @@ docker build github.com/docker/buildx#d4f088e
 
 ### URL queries
 
-Starting with Buildx v0.28 and BuildKit v0.24, URL queries are also supported.
-URL queries are more structured and recommended over [URL fragments](#url-fragments).
+Starting with Buildx v0.28, BuildKit v0.24 and Dockerfile v1.18, URL queries are
+also supported. URL queries are more structured and recommended over [URL fragments](#url-fragments):
 
-For example,
 ```console
 $ docker buildx build 'https://github.com/user/myrepo.git?branch=container&subdir=docker'
 ```
@@ -266,13 +265,29 @@ $ docker buildx build 'https://github.com/user/myrepo.git?branch=container&subdi
 | `myrepo.git?tag=mytag&subdir=myfolder`       | `refs/tags/mytag`             | `/myfolder`        |
 | `myrepo.git?branch=mybranch&subdir=myfolder` | `refs/heads/mybranch`         | `/myfolder`        |
 
-A commit hash can be specified as a `commit` or `checksum` query, along with `tag`, `branch`, or `ref`.
-A hash does not need to be a full hash.
+A commit hash can be specified as a `checksum` (alias `commit`) query, along
+`tag`, `branch`, or `ref` queries to verify that the reference resolves to the
+expected commit:
 
-```bash
-docker buildx build 'https://github.com/moby/buildkit.git?tag=v0.21.1&checksum=66735c67'
+```console
+$ docker buildx build 'https://github.com/moby/buildkit.git?tag=v0.21.1&checksum=66735c67'
+```
+
+If it doesn't match, the build fails:
+
+```console
+$ docker buildx build 'https://github.com/user/myrepo.git?tag=v0.1.0&commit=deadbeef'
+...
+#3 [internal] load git source https://github.com/user/myrepo.git?tag=v0.1.0-rc1&commit=deadbeef
+#3 0.484 bb41e835b6c3523c7c45b248cf4b45e7f862bc42       refs/tags/v0.1.0
+#3 ERROR: expected checksum to match deadbeef, got bb41e835b6c3523c7c45b248cf4b45e7f862bc42
 ```
 
+> [!NOTE]
+>
+> Short commit hash is supported with `checksum` (alias `commit`) query but for
+> `ref`, only the full hash of the commit is supported.
+
 #### Keep `.git` directory
 
 By default, BuildKit doesn't keep the `.git` directory when using Git contexts.