Europa: integrate core packages, separate universe

Signed-off-by: Solomon Hykes <solomon@dagger.io>

europa-universe/docker/build.cue

@@ -0,0 +1,97 @@
+package docker
+
+import (
+	"dagger.io/dagger"
+	"dagger.io/dagger/engine/spec/engine"
+)
+
+// Modular build API for Docker containers
+#Build: {
+	steps: [#Step, ...#Step]
+	output: #Image
+
+	// Generate build DAG from linerar steps
+	dag: {
+		for idx, step in steps {
+			// As a special case, wrap #Run into a valid step
+			if step.run != _|_ {
+				"\(idx)": {
+					input: _
+					run:   step & {
+						image: input
+						output: rootfs: _
+					}
+					output: {
+						config: input.config
+						rootfs: run.output.rootfs
+					}
+				}
+			}
+
+			// Otherwise, just use the step as is
+			if step.run == _|_ {
+				"\(idx)": {
+					run: false
+					step
+				}
+			}
+
+			// Either way, connect input to previous output
+			if idx > 0 {
+				"\(idx)": input: dag["\(idx-1)"].output
+			}
+		}
+	}
+
+	if len(dag) > 0 {
+		output: dag["\(len(dag)-1)"].output
+	}
+}
+
+// A build step is anything that produces a docker image
+#Step: {
+	input?: #Image
+	output: #Image
+	...
+} | #Run
+
+// Build step that copies files into the container image
+#Copy: {
+	input:    #Image
+	contents: dagger.#FS
+	source:   string | *"/"
+	dest:     string | *"/"
+
+	// Execute copy operation
+	copy: engine.#Copy & {
+		"input": input.rootfs
+		"source": {
+			root: contents
+			path: source
+		}
+		dest: copy.dest
+	}
+
+	output: #Image & {
+		config: input.config
+		rootfs: copy.output
+	}
+}
+
+// Build step that executes a Dockerfile
+#Dockerfile: {
+	// Source directory
+	source: dagger.#FS
+
+	// FIXME: not yet implemented
+	*{
+		// Look for Dockerfile in source at default path
+		path: "Dockerfile"
+	} | {
+		// Look for Dockerfile in source at a custom path
+		path: string
+	} | {
+		// Custom dockerfile  contents
+		contents: string
+	}
+}