config: add test for struct tags

This will fail a test if struct tags fall out of sync.

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

config/tags_test.go

@@ -0,0 +1,54 @@
+package config
+
+import (
+	"reflect"
+	"testing"
+)
+
+// TestTags checks that exported types and fields used in the root Config struct
+// have struct tags.
+func TestTags(t *testing.T) {
+	t.Logf("checking for: %v", wanttags)
+	nt := reflect.TypeOf(Config{})
+	t.Run(nt.Name(), func(t *testing.T) { typecheck(t, nt) })
+}
+
+var wanttags = []string{`json`, `yaml`}
+
+func typecheck(t *testing.T, typ reflect.Type) {
+	for i, lim := 0, typ.NumField(); i < lim; i++ {
+		f := typ.Field(i)
+		if f.PkgPath != "" {
+			// TODO(hank) Use the IsExported method once 1.16 support is
+			// dropped.
+			continue
+		}
+		// track the number of names for this field
+		vals := make(map[string]struct{})
+		// track which tag has which name
+		tagval := make(map[string]string)
+		for _, n := range wanttags {
+			if v, ok := f.Tag.Lookup(n); !ok {
+				t.Errorf("%s.%s: missing %q tag", typ.Name(), f.Name, n)
+			} else {
+				vals[v] = struct{}{}
+				tagval[n] = v
+			}
+		}
+		if len(vals) != 1 {
+			t.Errorf("different names for %q: %v", f.Name, tagval)
+		}
+		// Recurse on structs and pointers-to-structs.
+		switch nt := f.Type; nt.Kind() {
+		case reflect.Ptr:
+			pt := nt.Elem()
+			if pt.Kind() != reflect.Struct {
+				break
+			}
+			nt = nt.Elem()
+			fallthrough
+		case reflect.Struct:
+			t.Run(nt.Name(), func(t *testing.T) { typecheck(t, nt) })
+		}
+	}
+}