feat: set custom tag name for envPrefix (#332)

* Support other names for envPrefix

Co-authored-by: Sergey Kozlov <s.kozlov@ctrl2go.solutions>

Author: sv-kozlov

env.go

@@ -140,6 +140,9 @@ type Options struct {
 	// TagName specifies another tag name to use rather than the default 'env'.
 	TagName string
 
+	// PrefixTagName specifies another prefix tag name to use rather than the default 'envPrefix'.
+	PrefixTagName string
+
 	// DefaultValueTagName specifies another default tag name to use rather than the default 'envDefault'.
 	DefaultValueTagName string
 
@@ -178,6 +181,7 @@ func (opts *Options) getRawEnv(s string) string {
 func defaultOptions() Options {
 	return Options{
 		TagName:             "env",
+		PrefixTagName:       "envPrefix",
 		DefaultValueTagName: "envDefault",
 		Environment:         toMap(os.Environ()),
 		FuncMap:             defaultTypeParsers(),
@@ -190,6 +194,9 @@ func customOptions(opt Options) Options {
 	if opt.TagName == "" {
 		opt.TagName = defOpts.TagName
 	}
+	if opt.PrefixTagName == "" {
+		opt.PrefixTagName = defOpts.PrefixTagName
+	}
 	if opt.DefaultValueTagName == "" {
 		opt.DefaultValueTagName = defOpts.DefaultValueTagName
 	}
@@ -214,6 +221,7 @@ func optionsWithSliceEnvPrefix(opts Options, index int) Options {
 	return Options{
 		Environment:           opts.Environment,
 		TagName:               opts.TagName,
+		PrefixTagName:         opts.PrefixTagName,
 		DefaultValueTagName:   opts.DefaultValueTagName,
 		RequiredIfNoDef:       opts.RequiredIfNoDef,
 		OnSet:                 opts.OnSet,
@@ -228,10 +236,11 @@ func optionsWithEnvPrefix(field reflect.StructField, opts Options) Options {
 	return Options{
 		Environment:           opts.Environment,
 		TagName:               opts.TagName,
+		PrefixTagName:         opts.PrefixTagName,
 		DefaultValueTagName:   opts.DefaultValueTagName,
 		RequiredIfNoDef:       opts.RequiredIfNoDef,
 		OnSet:                 opts.OnSet,
-		Prefix:                opts.Prefix + field.Tag.Get("envPrefix"),
+		Prefix:                opts.Prefix + field.Tag.Get(opts.PrefixTagName),
 		UseFieldNameByDefault: opts.UseFieldNameByDefault,
 		FuncMap:               opts.FuncMap,
 		rawEnvVars:            opts.rawEnvVars,

env_test.go

@@ -2191,3 +2191,26 @@ func TestParseWithOptionsRenamedDefault(t *testing.T) {
 	isNoErr(t, Parse(cfg))
 	isEqual(t, "foo", cfg.Str)
 }
+
+func TestParseWithOptionsRenamedPrefix(t *testing.T) {
+	type Config struct {
+		Str string `env:"STR"`
+	}
+	type ComplexConfig struct {
+		Foo Config `envPrefix:"FOO_" myPrefix:"BAR_"`
+	}
+
+	t.Setenv("FOO_STR", "101")
+	t.Setenv("BAR_STR", "202")
+	t.Setenv("APP_BAR_STR", "303")
+
+	cfg := &ComplexConfig{}
+	isNoErr(t, ParseWithOptions(cfg, Options{PrefixTagName: "myPrefix"}))
+	isEqual(t, "202", cfg.Foo.Str)
+
+	isNoErr(t, ParseWithOptions(cfg, Options{PrefixTagName: "myPrefix", Prefix: "APP_"}))
+	isEqual(t, "303", cfg.Foo.Str)
+
+	isNoErr(t, Parse(cfg))
+	isEqual(t, "101", cfg.Foo.Str)
+}