If prior hooks.go is missing a func, append default version of it.

gengokit/handlers/hooks.go

@@ -45,9 +45,34 @@ func (h *HookRender) Render(_ string, _ *gengokit.Data) (io.Reader, error) {
 		return code, nil
 	}
 
+	// Note which hooks do not need to be added:
+	for _, d := range h.ast.Decls {
+		switch v := d.(type) {
+		case *ast.FuncDecl:
+			for _, h := range templates.Hooks {
+				if h.Name == v.Name.Name {
+					h.Code = ""
+					break
+				}
+			}
+		}
+	}
+
+	// Place to collect code for any missing hooks:
+	extra := new(bytes.Buffer)
+
+	for _, hd := range templates.Hooks {
+		if "" == hd.Code {
+			continue
+		}
+		// Add source code for this missing hook:
+		extra.WriteString(hd.Code)
+	}
+
 	if err := printer.Fprint(code, h.fset, h.ast); nil != err {
 		return nil, err
 	}
+	code.ReadFrom(extra)
 
 	return code, nil
 }