refactor(config): keep the re-export a function, pin env expansion in the test

pkg/config/binder/binder.go

@@ -16,7 +16,7 @@ import (
 // decoderConfigTagName sets the tag name to be used from the config structs
 // currently we only support "yaml" because we only support config loading
 // from yaml files and the yaml parser has no simple way to set a custom tag name to use
-var decoderConfigTagName = "yaml"
+const decoderConfigTagName = "yaml"
 
 // BindSourcesToStructs assigns any config value from a config file / env variable to struct `dst`.
 func BindSourcesToStructs(service string, dst any) error {
@@ -42,6 +42,8 @@ func BindSourcesToStructsFS(fileSystem fs.FS, filePath, service string, dst any)
 
 		return err
 	}
+	// the error is ignored on purpose, matching the pre-extraction behavior:
+	// an unparseable yaml file binds nothing instead of failing the startup
 	_ = cnf.LoadSources("yaml", yamlContent)
 
 	err = cnf.BindStruct("", &dst)

pkg/config/binder/binder_test.go

@@ -14,11 +14,13 @@ type TestConfig struct {
 }
 
 func TestBindSourcesToStructs(t *testing.T) {
-	// setup test env
+	// setup test env: one var set to pin env expansion, two deliberately
+	// unset to pin the defaults
+	t.Setenv("BINDER_TEST_SET_VAR", "from-env")
 	yaml := `
-a: "${FOO_VAR|no-foo}"
-b: "${BAR_VAR|no-bar}"
-c: "${CODE_VAR|code}"
+a: "${BINDER_TEST_SET_VAR|no-foo}"
+b: "${BINDER_TEST_UNSET_VAR|no-bar}"
+c: "${BINDER_TEST_OTHER_UNSET_VAR|code}"
 `
 	filePath := "etc/opencloud/foo.yaml"
 	fs := fstest.MapFS{
@@ -31,7 +33,7 @@ c: "${CODE_VAR|code}"
 		t.Error(err)
 	}
 
-	assert.Equal(t, c.A, "no-foo")
+	assert.Equal(t, c.A, "from-env")
 	assert.Equal(t, c.B, "no-bar")
 	assert.Equal(t, c.C, "code")
 }

pkg/config/helpers.go

@@ -7,8 +7,10 @@ import (
 )
 
 // BindSourcesToStructs assigns any config value from a config file / env variable to struct `dst`.
-// Backward-compatible re-export; the implementation lives in pkg/config/binder.
-var BindSourcesToStructs = binder.BindSourcesToStructs
+// The implementation lives in pkg/config/binder.
+func BindSourcesToStructs(service string, dst any) error {
+	return binder.BindSourcesToStructs(service, dst)
+}
 
 // LocalEndpoint returns the local endpoint for a given protocol and address.
 // Use it when configuring the reva runtime to get a service endpoint in the same