Accept String in av tag routines

... and avoid redundant writes if no changes need to be made.

rslib/src/backend/cardrendering.rs

@@ -22,7 +22,7 @@ impl CardRenderingService for Backend {
         &self,
         input: pb::ExtractAvTagsRequest,
     ) -> Result<pb::ExtractAvTagsResponse> {
-        let out = extract_av_tags(&input.text, input.question_side, self.i18n());
+        let out = extract_av_tags(input.text, input.question_side, self.i18n());
         Ok(pb::ExtractAvTagsResponse {
             text: out.0,
             av_tags: out.1,
@@ -117,7 +117,7 @@ impl CardRenderingService for Backend {
     }
 
     fn strip_av_tags(&self, input: pb::String) -> Result<pb::String> {
-        Ok(strip_av_tags(&input.val).into())
+        Ok(strip_av_tags(input.val).into())
     }
 
     fn render_markdown(&self, input: pb::RenderMarkdownRequest) -> Result<pb::String> {

rslib/src/browser_table.rs

@@ -271,7 +271,7 @@ impl RenderContext {
                 } => current_text,
             })
             .join("");
-        let question = prettify_av_tags(&qnodes_text);
+        let question = prettify_av_tags(qnodes_text);
 
         Ok(RenderContext {
             question,
@@ -411,7 +411,7 @@ impl RowContext {
                 } => current_text,
             })
             .join("");
-        let answer = prettify_av_tags(&answer);
+        let answer = prettify_av_tags(answer);
         html_to_text_line(
             if let Some(stripped) = answer.strip_prefix(&render_context.question) {
                 stripped

rslib/src/card_rendering/mod.rs

@@ -9,16 +9,36 @@ use crate::prelude::*;
 mod parser;
 mod writer;
 
-pub fn strip_av_tags(txt: &str) -> String {
-    CardNodes::parse(txt).write_without_av_tags()
+pub fn strip_av_tags<S: Into<String> + AsRef<str>>(txt: S) -> String {
+    nodes_or_text_only(txt.as_ref())
+        .map(|nodes| nodes.write_without_av_tags())
+        .unwrap_or_else(|| txt.into())
 }
 
-pub fn extract_av_tags(txt: &str, question_side: bool, tr: &I18n) -> (String, Vec<pb::AvTag>) {
-    CardNodes::parse(txt).write_and_extract_av_tags(question_side, tr)
+pub fn extract_av_tags<S: Into<String> + AsRef<str>>(
+    txt: S,
+    question_side: bool,
+    tr: &I18n,
+) -> (String, Vec<pb::AvTag>) {
+    nodes_or_text_only(txt.as_ref())
+        .map(|nodes| nodes.write_and_extract_av_tags(question_side, tr))
+        .unwrap_or_else(|| (txt.into(), vec![]))
 }
 
-pub fn prettify_av_tags(txt: &str) -> String {
-    CardNodes::parse(txt).write_with_pretty_av_tags()
+pub fn prettify_av_tags<S: Into<String> + AsRef<str>>(txt: S) -> String {
+    nodes_or_text_only(txt.as_ref())
+        .map(|nodes| nodes.write_with_pretty_av_tags())
+        .unwrap_or_else(|| txt.into())
+}
+
+/// Parse `txt` into [CardNodes] and return the result,
+/// or [None] if it is only a text node.
+fn nodes_or_text_only(txt: &str) -> Option<CardNodes> {
+    let nodes = CardNodes::parse(txt);
+    match nodes.0[..] {
+        [Node::Text(_)] => None,
+        _ => Some(nodes),
+    }
 }
 
 #[derive(Debug, PartialEq)]