acmego: allow arbitrary rc filters enclosed in [[ ]]

acme/acmego/main.go

@@ -22,6 +22,9 @@
 //
 //	.rs - rustfmt
 //
+// Alternatively, if the window tag contains text between "[[" and "]]"
+// then the encosed text is executed with rc -c. For example:
+// [[clang-format $1]].
 package main
 
 import (
@@ -70,6 +73,16 @@ func main() {
 		if event.Name == "" || event.Op != "put" {
 			continue
 		}
+
+		if w, err := acme.Open(event.ID, nil); err == nil {
+			if wi, err := w.Info(); err == nil {
+				if f := findFilter(wi.Tag); f != "" {
+					reformat(event.ID, event.Name, []string{"rc", "-c", f})
+					continue
+				}
+			}
+		}
+
 		for suffix, formatter := range formatters {
 			if strings.HasSuffix(event.Name, suffix) {
 				reformat(event.ID, event.Name, formatter)
@@ -256,3 +269,23 @@ func findLines(text []byte, start, end int) []byte {
 	endByte := i
 	return text[startByte:endByte]
 }
+
+func findFilter(tag string) string {
+	const (
+		tOpen  = "[["
+		tClose = "]]"
+	)
+	t0 := strings.Index(tag, tOpen)
+	if t0 == -1 {
+		return ""
+	}
+	if e := strings.Index(tag, "Edit"); e >= 0 && e < t0 {
+		// Err on the side of caution in case "[[" is part of an Edit command.
+		return ""
+	}
+	t1 := strings.Index(tag, tClose)
+	if t1 < t0 {
+		return ""
+	}
+	return tag[t0+len(tOpen) : t1]
+}