Add FSTag

static_tag.go

@@ -0,0 +1,48 @@
+package salix
+
+import (
+	"io"
+	"io/fs"
+	"path"
+
+	"go.elara.ws/salix/ast"
+)
+
+// FSTag writes files from an fs.FS to a template
+//
+// No escaping is done on the files, so make sure to avoid user-generated data.
+type FSTag struct {
+	// FS is the filesystem that files will be loaded from.
+	FS fs.FS
+
+	// PathPrefix is joined to the path string before a file is read.
+	PathPrefix string
+
+	// Extension is appended to the end of the path string before a file is read.
+	Extension string
+}
+
+func (ft FSTag) Run(tc *TagContext, block, args []ast.Node) error {
+	if len(args) != 1 {
+		return tc.PosError(tc.Tag, "expected one argument, got %d", len(args))
+	}
+
+	pathVal, err := tc.GetValue(args[0], nil)
+	if err != nil {
+		return err
+	}
+
+	pathStr, ok := pathVal.(string)
+	if !ok {
+		return tc.PosError(args[0], "expected string argument, got %T", pathVal)
+	}
+
+	fl, err := ft.FS.Open(path.Join(ft.PathPrefix, pathStr) + ft.Extension)
+	if err != nil {
+		return err
+	}
+	defer fl.Close()
+
+	_, err = io.Copy(tc, fl)
+	return err
+}