Add option remove `env_file` entry after merged

This avoids having a redundant `env_file` entry
output when rendering the compose file

Signed-off-by: Ulysses Souza <ulysses.souza@docker.com>

cli/compose/loader/loader.go

@@ -32,6 +32,14 @@ type Options struct {
 	SkipInterpolation bool
 	// Interpolation options
 	Interpolate *interp.Options
+	// Discard 'env_file' entries after resolving to 'environment' section
+	discardEnvFiles bool
+}
+
+// WithDiscardEnvFiles sets the Options to discard the `env_file` section after resolving to
+// the `environment` section
+func WithDiscardEnvFiles(opts *Options) {
+	opts.discardEnvFiles = true
 }
 
 // ParseYAML reads the bytes from a file, parses the bytes into a mapping
@@ -105,6 +113,11 @@ func Load(configDetails types.ConfigDetails, options ...func(*Options)) (*types.
 			return nil, err
 		}
 		cfg.Filename = file.Filename
+		if opts.discardEnvFiles {
+			for i := range cfg.Services {
+				cfg.Services[i].EnvFile = nil
+			}
+		}
 
 		configs = append(configs, cfg)
 	}

cli/compose/loader/loader_test.go

@@ -759,6 +759,38 @@ services:
 	assert.Check(t, is.DeepEqual([]string{"build", "links", "pid"}, unsupported))
 }
 
+func TestDiscardEnvFileOption(t *testing.T) {
+	dict, err := ParseYAML([]byte(`version: "3"
+services:
+  web:
+    image: nginx
+    env_file:
+     - example1.env
+     - example2.env
+`))
+	expectedEnvironmentMap := types.MappingWithEquals{
+		"FOO": strPtr("foo_from_env_file"),
+		"BAZ": strPtr("baz_from_env_file"),
+		"BAR": strPtr("bar_from_env_file_2"), // Original value is overwritten by example2.env
+		"QUX": strPtr("quz_from_env_file_2"),
+	}
+	assert.NilError(t, err)
+	configDetails := buildConfigDetails(dict, nil)
+
+	// Default behavior keeps the `env_file` entries
+	configWithEnvFiles, err := Load(configDetails)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, configWithEnvFiles.Services[0].EnvFile, types.StringList{"example1.env",
+		"example2.env"})
+	assert.DeepEqual(t, configWithEnvFiles.Services[0].Environment, expectedEnvironmentMap)
+
+	// Custom behavior removes the `env_file` entries
+	configWithoutEnvFiles, err := Load(configDetails, WithDiscardEnvFiles)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, configWithoutEnvFiles.Services[0].EnvFile, types.StringList(nil))
+	assert.DeepEqual(t, configWithoutEnvFiles.Services[0].Environment, expectedEnvironmentMap)
+}
+
 func TestBuildProperties(t *testing.T) {
 	dict, err := ParseYAML([]byte(`
 version: "3"