Mark Dockerfile as requiring BuildKit (#12541)

jaywink · David Robertson · web-flow · commit 706456de1f63 · 2022-04-26T15:31:52.000+01:00
Co-authored-by: David Robertson &lt;davidr@element.io&gt;
diff --git a/changelog.d/12541.docker b/changelog.d/12541.docker
@@ -0,0 +1 @@
+Explicitly opt-in to using [BuildKit-specific features](https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/syntax.md) in the Dockerfile. This fixes issues with building images in some GitLab CI environments.
diff --git a/docker/Dockerfile b/docker/Dockerfile
@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Dockerfile to build the matrixdotorg/synapse docker images.
 #
 # Note that it uses features which are only available in BuildKit - see

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Explicitly opt-in to using [BuildKit-specific features](https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/syntax.md) in the Dockerfile. This fixes issues with building images in some GitLab CI environments.`
Original file line number	Diff line number	Diff line change
`@@ -1,3 +1,4 @@`
	`1`	`+# syntax=docker/dockerfile:1`
`1`	`2`	`# Dockerfile to build the matrixdotorg/synapse docker images.`
`2`	`3`	`#`
`3`	`4`	`# Note that it uses features which are only available in BuildKit - see`