dir2config: switch to includes instead of ad-hoc defaults

cmd/dkl-dir2config/search-list.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"sort"
+)
+
+var searchList = make([]FS, 0)
+
+// read the first file matching path in the search list
+func read(path string) (ba []byte, err error) {
+	for _, fs := range searchList {
+		var r io.ReadCloser
+		r, err = fs.Open(path)
+		if os.IsNotExist(err) {
+			continue
+		}
+		if err != nil {
+			return
+		}
+
+		defer r.Close()
+		return ioutil.ReadAll(r)
+	}
+
+	err = fmt.Errorf("%s: %w", path, os.ErrNotExist)
+	return
+}
+
+func listBase(path string) ([]string, error) {
+	return fsFS{base}.List(path)
+}
+
+func listMerged(path string) (entries []string, err error) {
+	seen := map[string]bool{}
+	for _, fs := range searchList {
+		var fsEnts []string
+		fsEnts, err = fs.List(path)
+		if os.IsNotExist(err) {
+			err = nil
+			continue
+		}
+		if err != nil {
+			return
+		}
+
+		for _, ent := range fsEnts {
+			if !seen[ent] {
+				entries = append(entries, ent)
+				seen[ent] = true
+			}
+		}
+	}
+
+	sort.Strings(entries)
+	return
+}