Change compose file handling to require valid service specifications

Added the checks and some tests
One of the tests wasn't valid docker-compose.yml, that's been changed.
Bad config throws an error and has a test

Signed-off-by: Jack Laxson <jackjrabbit@gmail.com>

bake/compose.go

@@ -1,6 +1,8 @@
 package bake
 
 import (
+	"fmt"
+
 	"github.com/docker/cli/cli/compose/loader"
 	composetypes "github.com/docker/cli/cli/compose/types"
 )
@@ -33,7 +35,7 @@ func ParseCompose(dt []byte) (*Config, error) {
 		var g Group
 
 		for _, s := range cfg.Services {
-			g.Targets = append(g.Targets, s.Name)
+
 			var contextPathP *string
 			if s.Build.Context != "" {
 				contextPath := s.Build.Context
@@ -44,6 +46,15 @@ func ParseCompose(dt []byte) (*Config, error) {
 				dockerfilePath := s.Build.Dockerfile
 				dockerfilePathP = &dockerfilePath
 			}
+			// Check if there's actually a dockerfile mentioned
+			if dockerfilePathP == nil && contextPathP == nil {
+				// if not make sure they're setting an image or it's invalid d-c.yml
+				if s.Image == "" {
+					return nil, fmt.Errorf("Compose file invalid: Service %s has neither an image nor a build context specified. At least one must be provided.", s.Name)
+				}
+				break
+			}
+			g.Targets = append(g.Targets, s.Name)
 			t := Target{
 				Context:    contextPathP,
 				Dockerfile: dockerfilePathP,

bake/compose_test.go

@@ -40,6 +40,22 @@ services:
 	require.Equal(t, "123", c.Target["webapp"].Args["buildno"])
 }
 
+func TestNoBuildOutOfTreeService(t *testing.T) {
+	var dt = []byte(`
+version: "3.7"
+
+services:
+    external:
+        image: "verycooldb:1337"
+    webapp:
+        build: ./db
+`)
+	c, err := ParseCompose(dt)
+	require.NoError(t, err)
+	require.Equal(t, 1, len(c.Group))
+
+}
+
 func TestParseComposeTarget(t *testing.T) {
 	var dt = []byte(`
 version: "3.7"
@@ -47,9 +63,11 @@ version: "3.7"
 services:
   db:
     build:
+      context: ./db
       target: db
   webapp:
     build:
+      context: .
       target: webapp
 `)
 
@@ -59,3 +77,21 @@ services:
 	require.Equal(t, "db", *c.Target["db"].Target)
 	require.Equal(t, "webapp", *c.Target["webapp"].Target)
 }
+
+func TestBogusCompose(t *testing.T) {
+	var dt = []byte(`
+version: "3.7"
+
+services:
+  db:
+    build:
+      target: db
+  webapp:
+    build:
+      context: .
+      target: webapp
+`)
+
+	_, err := ParseCompose(dt)
+	require.Error(t, err)
+}

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

@@ -7,6 +7,7 @@ services:
     image: docker.io/tonistiigi/db
   webapp:
     build:
+      context: .
       dockerfile: Dockerfile.webapp
       args:
         buildno: 1