Modify card rendering output to specify if rendered card is empty (#3890)

* modify render_card to return whether card was empty

* plumbing

* add flag to proto message

* plumbing: pass flag along to PartiallyRenderedCard

* add tests

* Use a custom return type for clarity (dae)

proto/anki/card_rendering.proto

@@ -127,6 +127,7 @@ message RenderCardResponse {
   repeated RenderedTemplateNode answer_nodes = 2;
   string css = 3;
   bool latex_svg = 4;
+  bool is_empty = 5;
 }
 
 message RenderedTemplateNode {

pylib/anki/template.py

@@ -60,6 +60,7 @@ class PartiallyRenderedCard:
     anodes: TemplateReplacementList
     css: str
     latex_svg: bool
+    is_empty: bool
 
     @classmethod
     def from_proto(
@@ -68,7 +69,9 @@ class PartiallyRenderedCard:
         qnodes = cls.nodes_from_proto(out.question_nodes)
         anodes = cls.nodes_from_proto(out.answer_nodes)
 
-        return PartiallyRenderedCard(qnodes, anodes, out.css, out.latex_svg)
+        return PartiallyRenderedCard(
+            qnodes, anodes, out.css, out.latex_svg, out.is_empty
+        )
 
     @staticmethod
     def nodes_from_proto(

rslib/src/card_rendering/service.rs

@@ -219,6 +219,7 @@ impl From<RenderCardOutput> for anki_proto::card_rendering::RenderCardResponse {
             answer_nodes: rendered_nodes_to_proto(o.anodes),
             css: o.css,
             latex_svg: o.latex_svg,
+            is_empty: o.is_empty,
         }
     }
 }

rslib/src/notetype/render.rs

@@ -20,6 +20,7 @@ pub struct RenderCardOutput {
     pub anodes: Vec<RenderedNode>,
     pub css: String,
     pub latex_svg: bool,
+    pub is_empty: bool,
 }
 
 impl RenderCardOutput {
@@ -136,7 +137,7 @@ impl Collection {
             )
         };
 
-        let (qnodes, anodes) = render_card(RenderCardRequest {
+        let response = render_card(RenderCardRequest {
             qfmt,
             afmt,
             field_map: &field_map,
@@ -147,10 +148,11 @@ impl Collection {
             partial_render,
         })?;
         Ok(RenderCardOutput {
-            qnodes,
-            anodes,
+            qnodes: response.qnodes,
+            anodes: response.anodes,
             css: nt.config.css.clone(),
             latex_svg: nt.config.latex_svg,
+            is_empty: response.is_empty,
         })
     }
 

rslib/src/template.rs

@@ -592,6 +592,13 @@ pub struct RenderCardRequest<'a> {
     pub partial_render: bool,
 }
 
+pub struct RenderCardResponse {
+    pub qnodes: Vec<RenderedNode>,
+    pub anodes: Vec<RenderedNode>,
+    pub is_empty: bool,
+}
+
+/// Returns `(qnodes, anodes, is_empty)`
 pub fn render_card(
     RenderCardRequest {
         qfmt,
@@ -603,7 +610,7 @@ pub fn render_card(
         tr,
         partial_render: partial_for_python,
     }: RenderCardRequest<'_>,
-) -> Result<(Vec<RenderedNode>, Vec<RenderedNode>)> {
+) -> Result<RenderCardResponse> {
     // prepare context
     let mut context = RenderContext {
         fields: field_map,
@@ -638,7 +645,11 @@ pub fn render_card(
     };
     if let Some(text) = empty_message {
         qnodes.push(RenderedNode::Text { text: text.clone() });
-        return Ok((qnodes, vec![RenderedNode::Text { text }]));
+        return Ok(RenderCardResponse {
+            qnodes,
+            anodes: vec![RenderedNode::Text { text }],
+            is_empty: true,
+        });
     }
 
     // answer side
@@ -654,7 +665,11 @@ pub fn render_card(
         .and_then(|tmpl| tmpl.render(&context, tr))
         .map_err(|e| template_error_to_anki_error(e, false, browser, tr))?;
 
-    Ok((qnodes, anodes))
+    Ok(RenderCardResponse {
+        qnodes,
+        anodes,
+        is_empty: false,
+    })
 }
 
 fn cloze_is_empty(field_map: &HashMap<&str, Cow<str>>, card_ord: u16) -> bool {
@@ -1338,14 +1353,15 @@ mod test {
             tr: &tr,
             partial_render: true,
         };
-        let qnodes = super::render_card(req.clone()).unwrap().0;
+        let response = super::render_card(req.clone()).unwrap();
         assert_eq!(
-            qnodes[0],
+            response.qnodes[0],
             FN::Text {
                 text: "test".into()
             }
         );
-        if let FN::Text { ref text } = qnodes[1] {
+        assert!(response.is_empty);
+        if let FN::Text { ref text } = response.qnodes[1] {
             assert!(text.contains("card is blank"));
         } else {
             unreachable!();
@@ -1354,9 +1370,9 @@ mod test {
         // a popular card template expects {{FrontSide}} to resolve to an empty
         // string on the front side :-(
         req.qfmt = "{{FrontSide}}{{N}}";
-        let qnodes = super::render_card(req.clone()).unwrap().0;
+        let response = super::render_card(req.clone()).unwrap();
         assert_eq!(
-            &qnodes,
+            &response.qnodes,
             &[
                 FN::Replacement {
                     field_name: "FrontSide".into(),
@@ -1366,8 +1382,10 @@ mod test {
                 FN::Text { text: "N".into() }
             ]
         );
+        assert!(!response.is_empty);
         req.partial_render = false;
-        let qnodes = super::render_card(req.clone()).unwrap().0;
-        assert_eq!(&qnodes, &[FN::Text { text: "N".into() }]);
+        let response = super::render_card(req.clone()).unwrap();
+        assert_eq!(&response.qnodes, &[FN::Text { text: "N".into() }]);
+        assert!(!response.is_empty);
     }
 }