Add ~emersion/go-scfg as a subdirectory

1 files changed, 79 insertions, 0 deletions

diff --git a/scfg/struct.go b/scfg/struct.go
new file mode 100644
index 0000000..8b39e34
--- /dev/null
+++ b/scfg/struct.go
@@ -0,0 +1,79 @@
+package scfg
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"sync"
+)
+
+// structInfo contains scfg metadata for structs.
+type structInfo struct {
+	param    int            // index of field storing parameters
+	children map[string]int // indices of fields storing child directives
+}
+
+var (
+	structCacheMutex sync.Mutex
+	structCache      = make(map[reflect.Type]*structInfo)
+)
+
+func getStructInfo(t reflect.Type) (*structInfo, error) {
+	structCacheMutex.Lock()
+	defer structCacheMutex.Unlock()
+
+	if info := structCache[t]; info != nil {
+		return info, nil
+	}
+
+	info := &structInfo{
+		param:    -1,
+		children: make(map[string]int),
+	}
+
+	for i := 0; i < t.NumField(); i++ {
+		f := t.Field(i)
+		if f.Anonymous {
+			return nil, fmt.Errorf("scfg: anonymous struct fields are not supported")
+		} else if !f.IsExported() {
+			continue
+		}
+
+		tag := f.Tag.Get("scfg")
+		parts := strings.Split(tag, ",")
+		k, options := parts[0], parts[1:]
+		if k == "-" {
+			continue
+		} else if k == "" {
+			k = f.Name
+		}
+
+		isParam := false
+		for _, opt := range options {
+			switch opt {
+			case "param":
+				isParam = true
+			default:
+				return nil, fmt.Errorf("scfg: invalid option %q in struct tag", opt)
+			}
+		}
+
+		if isParam {
+			if info.param >= 0 {
+				return nil, fmt.Errorf("scfg: param option specified multiple times in struct tag in %v", t)
+			}
+			if parts[0] != "" {
+				return nil, fmt.Errorf("scfg: name must be empty when param option is specified in struct tag in %v", t)
+			}
+			info.param = i
+		} else {
+			if _, ok := info.children[k]; ok {
+				return nil, fmt.Errorf("scfg: key %q specified multiple times in struct tag in %v", k, t)
+			}
+			info.children[k] = i
+		}
+	}
+
+	structCache[t] = info
+	return info, nil
+}