fix(compose): keep build-only services when Up starts a subset

modules/compose/compose_api.go

@@ -7,7 +7,6 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -321,17 +320,16 @@ func (d *DockerCompose) Up(ctx context.Context, opts ...StackUpOption) (err erro
 	}
 
 	if len(upOptions.Services) != len(d.project.Services) {
-		sort.Strings(upOptions.Services)
-
-		filteredServices := types.Services{}
-
-		for _, srv := range upOptions.Services {
-			if srvConfig, ok := d.project.Services[srv]; ok {
-				filteredServices[srv] = srvConfig
-			}
+		// Disable (rather than delete) the non-selected services so a selected
+		// service's `service:` additional build-contexts stay resolvable at build
+		// time; only the selected services are created and started.
+		// IgnoreDependencies excludes their runtime depends_on from the selection.
+		d.project, err = d.project.WithSelectedServices(upOptions.Services, types.IgnoreDependencies)
+		if err != nil {
+			return err
 		}
-
-		d.project.Services = filteredServices
+		// WithSelectedServices returns a new project; point the up options at it too.
+		upOptions.Project = d.project
 	}
 
 	err = d.composeService.Up(ctx, d.project, api.UpOptions{

modules/compose/compose_api_test.go

@@ -107,6 +107,37 @@ func TestDockerComposeAPIWithRunServices(t *testing.T) {
 	assert.Contains(t, serviceNames, "api-nginx")
 }
 
+func TestDockerComposeAPIWithRunServicesAndServiceBuildContext(t *testing.T) {
+	// "app" builds with a `service:build-dep` additional build context, so the
+	// build needs build-dep to remain in the project even though RunServices
+	// selects only "app" and build-dep is never started as a container.
+	//
+	// Regression test: Up used to shrink d.project down to the selected
+	// services, which dropped the build-only build-dep service and made the
+	// build fail with "service ... declares unknown service ... as additional
+	// contexts" — even though `docker compose up app` on the same project works.
+	path := filepath.Join(testdataPackage, "docker-compose-service-build-context.yml")
+	compose, err := NewDockerCompose(path)
+	require.NoError(t, err, "NewDockerCompose()")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+
+	err = compose.
+		WaitForService("app", wait.ForHTTP("/env").WithPort("8080/tcp")).
+		Up(ctx, Wait(true), RunServices("app"))
+	cleanup(t, compose)
+	require.NoError(t, err, "compose.Up()")
+
+	// Only the selected runtime service is started; the build-only context is not.
+	serviceNames := compose.Services()
+	require.Len(t, serviceNames, 1)
+	assert.Contains(t, serviceNames, "app")
+
+	_, err = compose.ServiceContainer(context.Background(), "build-dep")
+	require.Error(t, err, "build-dep is a build-only context and must not be started")
+}
+
 func TestDockerComposeAPIWithProfiles(t *testing.T) {
 	path := RenderComposeProfiles(t)
 

modules/compose/testdata/docker-compose-service-build-context.yml

@@ -0,0 +1,16 @@
+services:
+  # build-only dependency: never started, only used as a build context by "app".
+  build-dep:
+    build:
+      context: .
+      dockerfile: service-build-context-dep.Dockerfile
+    image: testcontainers/compose-service-build-dep:latest
+  app:
+    build:
+      context: .
+      dockerfile: service-build-context-app.Dockerfile
+      additional_contexts:
+        build-dep: service:build-dep
+    image: testcontainers/compose-service-build-app:latest
+    ports:
+      - "8080/tcp"

modules/compose/testdata/service-build-context-app.Dockerfile

@@ -0,0 +1,6 @@
+FROM golang:1.24-alpine@sha256:fc2cff6625f3c1c92e6c85938ac5bd09034ad0d4bc2dfb08278020b68540dbb5
+WORKDIR /app
+# Consumes the `service:build-dep` additional build context.
+COPY --from=build-dep /artifact /artifact
+COPY echoserver.go .
+CMD go run echoserver.go

modules/compose/testdata/service-build-context-dep.Dockerfile

@@ -0,0 +1,2 @@
+FROM golang:1.24-alpine@sha256:fc2cff6625f3c1c92e6c85938ac5bd09034ad0d4bc2dfb08278020b68540dbb5
+RUN echo "service-build-context-dep" > /artifact