Validate compose v2 input

Compose v1 has input validation but in the composev2
merge function validation was missing so added it.

Fixes #357

Signed-off-by: Suraj Deshmukh <surajssd009005@gmail.com>
Signed-off-by: Vincent Demeester <vincent@sbr.pm>

Author: surajssd

config/merge_v2.go

@@ -3,6 +3,7 @@ package config
 import (
 	"fmt"
 	"path"
+	"strings"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/libcompose/utils"
@@ -49,6 +50,19 @@ func MergeServicesV2(existingServices *ServiceConfigs, environmentLookup Environ
 		datas[name] = data
 	}
 
+	if options.Validate {
+		var errs []string
+		for name, data := range datas {
+			err := validateServiceConstraintsv2(data, name)
+			if err != nil {
+				errs = append(errs, err.Error())
+			}
+		}
+		if len(errs) != 0 {
+			return nil, fmt.Errorf(strings.Join(errs, "\n"))
+		}
+	}
+
 	serviceConfigs := make(map[string]*ServiceConfig)
 	if err := utils.Convert(datas, &serviceConfigs); err != nil {
 		return nil, err

config/validation.go

@@ -287,3 +287,36 @@ func validateServiceConstraints(service RawService, serviceName string) error {
 
 	return nil
 }
+
+func validateServiceConstraintsv2(service RawService, serviceName string) error {
+	if err := setupSchemaLoaders(servicesSchemaDataV2, &schemaV2, &schemaLoaderV2, &constraintSchemaLoaderV2); err != nil {
+		return err
+	}
+
+	service = convertServiceKeysToStrings(service)
+
+	var validationErrors []string
+
+	dataLoader := gojsonschema.NewGoLoader(service)
+
+	result, err := gojsonschema.Validate(constraintSchemaLoaderV2, dataLoader)
+	if err != nil {
+		return err
+	}
+
+	if !result.Valid() {
+		for _, err := range result.Errors() {
+			if err.Type() == "required" {
+				_, containsImage := service["image"]
+				_, containsBuild := service["build"]
+
+				if containsBuild || !containsImage && !containsBuild {
+					validationErrors = append(validationErrors, fmt.Sprintf("Service '%s' has neither an image nor a build context specified. At least one must be provided.", serviceName))
+				}
+			}
+		}
+		return fmt.Errorf(strings.Join(validationErrors, "\n"))
+	}
+
+	return nil
+}