drop all comments from yaml file before applying string substitutions

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

loader/loader.go

@@ -217,16 +217,35 @@ func Load(configDetails types.ConfigDetails, options ...func(*Options)) (*types.
 
 func parseConfig(b []byte, opts *Options) (map[string]interface{}, error) {
 	if !opts.SkipInterpolation {
-		substitute, err := opts.Interpolate.Substitute(string(b), template.Mapping(opts.Interpolate.LookupValue))
+		withoutComments, err := removeYamlComments(b)
 		if err != nil {
 			return nil, err
 		}
-		b = []byte(substitute)
+
+		substituted, err := opts.Interpolate.Substitute(string(withoutComments), template.Mapping(opts.Interpolate.LookupValue))
+		if err != nil {
+			return nil, err
+		}
+		b = []byte(substituted)
 	}
 
 	return ParseYAML(b)
 }
 
+// removeYamlComments drop all comments from the yaml file, so we don't try to apply string substitutions on irrelevant places
+func removeYamlComments(b []byte) ([]byte, error) {
+	var cfg interface{}
+	err := yaml.Unmarshal(b, &cfg)
+	if err != nil {
+		return nil, err
+	}
+	b, err = yaml.Marshal(cfg)
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}
+
 func groupXFieldsIntoExtensions(dict map[string]interface{}) map[string]interface{} {
 	extras := map[string]interface{}{}
 	for key, value := range dict {

loader/loader_test.go

@@ -480,6 +480,7 @@ services:
 func TestLoadWithEnvironmentInterpolation(t *testing.T) {
 	home := "/home/foo"
 	config, err := loadYAMLWithEnv(`
+# This is a comment, so using variable syntax here ${SHOULD_NOT_BREAK} parsing
 services:
   test:
     image: busybox

template/template.go

@@ -61,7 +61,7 @@ type Mapping func(string) (string, bool)
 // the substitution and an error.
 type SubstituteFunc func(string, Mapping) (string, bool, error)
 
-// SubstituteWith subsitute variables in the string with their values.
+// SubstituteWith substitute variables in the string with their values.
 // It accepts additional substitute function.
 func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, subsFuncs ...SubstituteFunc) (string, error) {
 	var err error