ci: cleaner pattern for sharing base images across actions

Signed-off-by: Sam Alba <samalba@users.noreply.github.com>

ci/images.cue

@@ -8,10 +8,11 @@ let GoVersion = "1.17"
 let GolangCILintVersion = "1.44.0"
 
 // Base container images used for the CI
-images: {
+#Images: {
 
 	// base image to build go binaries
-	goBuilder: docker.#Build & {
+	goBuilder:  _goBuilder.output
+	_goBuilder: docker.#Build & {
 		_packages: ["bash", "git"]
 
 		steps: [
@@ -35,7 +36,8 @@ images: {
 
 	// base image for the Go linter
 	// https://golangci-lint.run/usage/install/#docker
-	goLinter: docker.#Build & {
+	goLinter:  _goLinter.output
+	_goLinter: docker.#Build & {
 		steps: [
 			docker.#Pull & {
 				source: "index.docker.io/golangci/golangci-lint:v\(GolangCILintVersion)"

ci/main.cue

@@ -33,6 +33,8 @@ engine.#Plan & {
 			id: "go mod cache"
 		}
 
+		baseImages: #Images
+
 		source: "dagger source code": {
 			contents: inputs.directories.source.contents
 			dest:     "/usr/src/dagger"
@@ -40,7 +42,7 @@ engine.#Plan & {
 
 		// FIXME: build only if the linter passed
 		build: bash.#Run & {
-			input: images.goBuilder.output
+			input: baseImages.goBuilder
 
 			env: {
 				GOMODCACHE: mounts["go mod cache"].dest
@@ -71,7 +73,7 @@ engine.#Plan & {
 		}
 
 		goLint: bash.#Run & {
-			input: images.goLinter.output
+			input: baseImages.goLinter
 
 			// FIXME: the source volume is too slow, taking >3m on docker for mac (vs < 2sec on the host machine)
 			script: contents: "golangci-lint run -v --timeout 5m"