Make docker/cli image overrideable

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

pkg/universe.dagger.io/docker/cli/client.cue

@@ -5,17 +5,21 @@ import (
 	"universe.dagger.io/docker"
 )
 
-// See https://github.com/dagger/dagger/issues/1856
+// See https://github.com/dagger/dagger/discussions/1874
+
+// Default image
+#Image: docker.#Pull & {
+	source: "docker:20.10.13-alpine3.15"
+}
 
 // Run a docker CLI command
 #Run: {
 	#RunSocket | #RunSSH | #RunTCP
 
-	_image: docker.#Pull & {
+	_defaultImage: #Image
-		source: "docker:20.10.13-alpine3.15"
-	}
 
-	input: _image.output
+	// As a convenience, input defaults to a ready-to-use docker environment
+	input: docker.#Image | *_defaultImage.output
 }
 
 // Connect via local docker socket

pkg/universe.dagger.io/docker/cli/test/run.cue

@@ -4,6 +4,7 @@ import (
 	"dagger.io/dagger"
 
 	"universe.dagger.io/alpine"
+	"universe.dagger.io/docker"
 	"universe.dagger.io/docker/cli"
 )
 
@@ -17,19 +18,27 @@ dagger.#Plan & {
 		}
 
 		differentImage: {
-			_cli: alpine.#Build & {
+			_cli: docker.#Build & {
-				packages: {
+				steps: [
-					bash: {}
+					alpine.#Build & {
-					"docker-cli": {}
+						packages: "docker-cli": {}
-				}
+					},
+					docker.#Run & {
+						command: {
+							name: "sh"
+							flags: "-c": "echo -n foobar > /test.txt"
+						}
+					},
+				]
 			}
-			run: cli.#RunSocket & {
+			run: cli.#Run & {
 				input: _cli.output
 				host:  client.filesystem."/var/run/docker.sock".read.contents
 				command: {
 					name: "docker"
 					args: ["info"]
 				}
+				export: files: "/test.txt": "foobar"
 			}
 		}