bake: initial implementation

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

hack/demo-env/examples/compose/Dockerfile

@@ -0,0 +1,2 @@
+FROM alpine:3.8
+RUN echo "this is db"

hack/demo-env/examples/compose/Dockerfile.webapp

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+FROM alpine:3.8
+COPY Dockerfile /
+RUN env

hack/demo-env/examples/compose/compose.yml

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+version: "3"
+
+services:
+  db:
+    build: .
+    command: ./entrypoint.sh
+    image: docker.io/tonistiigi/db
+  webapp:
+    build:
+      dockerfile: Dockerfile.webapp
+      args:
+        buildno: 1

hack/demo-env/examples/compose/config.hcl

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+group "default" {
+	targets = ["db", "webapp"]
+}
+
+group "release" {
+	targets = ["db", "webapp-plus"]
+}
+
+target "db" {
+	context = "./"
+	tags = ["docker.io/tonistiigi/db"]
+}
+
+target "webapp" {
+	context = "./"
+	dockerfile = "Dockerfile.webapp"
+	args = {
+		buildno = "123"
+	}
+}
+
+target "cross" {
+	platforms = [
+		"linux/amd64",
+		"linux/arm64"
+	]
+}
+
+target "webapp-plus" {
+	inherits = ["webapp", "cross"]
+	args = {
+		IAMPLUS = "true"
+	}
+}

hack/demo-env/examples/simple1/Dockerfile

@@ -1,2 +1,4 @@
 FROM alpine
-RUN touch foo
+RUN apk add --no-cache curl
+WORKDIR /src
+COPY . .