Rework RenderCardOutput::question/answer

Instead of flattening the output (which was missing FrontSide), alter
the behaviour of render() instead. The non-partial output is now exposed
via Protobuf, so the non-Python clients can take advantage of it.

proto/anki/card_rendering.proto

@@ -93,6 +93,10 @@ message EmptyCardsReport {
 message RenderExistingCardRequest {
   int64 card_id = 1;
   bool browser = 2;
+  // If true, rendering will stop when an unknown filter is encountered,
+  // and caller will need to complete rendering. This is done to allow
+  // Python code to modify the rendering.
+  bool partial_render = 3;
 }
 
 message RenderUncommittedCardRequest {
@@ -100,6 +104,10 @@ message RenderUncommittedCardRequest {
   uint32 card_ord = 2;
   notetypes.Notetype.Template template = 3;
   bool fill_empty = 4;
+  // If true, rendering will stop when an unknown filter is encountered,
+  // and caller will need to complete rendering. This is done to allow
+  // Python code to modify the rendering.
+  bool partial_render = 5;
 }
 
 message RenderUncommittedCardLegacyRequest {
@@ -107,6 +115,10 @@ message RenderUncommittedCardLegacyRequest {
   uint32 card_ord = 2;
   bytes template = 3;
   bool fill_empty = 4;
+  // If true, rendering will stop when an unknown filter is encountered,
+  // and caller will need to complete rendering. This is done to allow
+  // Python code to modify the rendering.
+  bool partial_render = 5;
 }
 
 message RenderCardResponse {

pylib/anki/template.py

@@ -262,6 +262,7 @@ class TemplateRenderContext:
                 card_ord=self._card.ord,
                 template=to_json_bytes(self._template),
                 fill_empty=self._fill_empty,
+                partial_render=True,
             )
             # when rendering card layout, the css changes have not been
             # committed; we need the current notetype instance instead
@@ -269,7 +270,7 @@ class TemplateRenderContext:
         else:
             # existing card (eg study mode)
             out = self._col._backend.render_existing_card(
-                card_id=self._card.id, browser=self._browser
+                card_id=self._card.id, browser=self._browser, partial_render=True
             )
         return PartiallyRenderedCard.from_proto(out)
 

rslib/src/browser_table.rs

@@ -257,7 +257,7 @@ impl RenderContext {
     fn new(col: &mut Collection, card: &Card, note: &Note, notetype: &Notetype) -> Self {
         match notetype
             .get_template(card.template_idx)
-            .and_then(|template| col.render_card(note, card, notetype, template, true))
+            .and_then(|template| col.render_card(note, card, notetype, template, true, true))
         {
             Ok(render) => RenderContext::Ok {
                 question: rendered_nodes_to_str(&render.qnodes),

rslib/src/card_rendering/service.rs

@@ -90,7 +90,7 @@ impl crate::services::CardRenderingService for Collection {
         &mut self,
         input: anki_proto::card_rendering::RenderExistingCardRequest,
     ) -> Result<anki_proto::card_rendering::RenderCardResponse> {
-        self.render_existing_card(CardId(input.card_id), input.browser)
+        self.render_existing_card(CardId(input.card_id), input.browser, input.partial_render)
             .map(Into::into)
     }
 
@@ -103,7 +103,7 @@ impl crate::services::CardRenderingService for Collection {
         let ord = input.card_ord as u16;
         let fill_empty = input.fill_empty;
 
-        self.render_uncommitted_card(&mut note, &template, ord, fill_empty)
+        self.render_uncommitted_card(&mut note, &template, ord, fill_empty, input.partial_render)
             .map(Into::into)
     }
 
@@ -117,7 +117,7 @@ impl crate::services::CardRenderingService for Collection {
         let ord = input.card_ord as u16;
         let fill_empty = input.fill_empty;
 
-        self.render_uncommitted_card(&mut note, &template, ord, fill_empty)
+        self.render_uncommitted_card(&mut note, &template, ord, fill_empty, input.partial_render)
             .map(Into::into)
     }
 

rslib/src/cloze.rs

@@ -410,14 +410,14 @@ fn strip_html_inside_mathjax(text: &str) -> Cow<str> {
 
 pub(crate) fn cloze_filter<'a>(text: &'a str, context: &RenderContext) -> Cow<'a, str> {
     strip_html_inside_mathjax(
-        reveal_cloze_text(text, context.card_ord + 1, context.question_side).as_ref(),
+        reveal_cloze_text(text, context.card_ord + 1, context.frontside.is_none()).as_ref(),
     )
     .into_owned()
     .into()
 }
 
 pub(crate) fn cloze_only_filter<'a>(text: &'a str, context: &RenderContext) -> Cow<'a, str> {
-    reveal_cloze_text_only(text, context.card_ord + 1, context.question_side)
+    reveal_cloze_text_only(text, context.card_ord + 1, context.frontside.is_none())
 }
 
 #[cfg(test)]

rslib/src/import_export/text/csv/export.rs

@@ -69,7 +69,8 @@ impl Collection {
     }
 
     fn card_record(&mut self, card: CardId, with_html: bool) -> Result<[String; 2]> {
-        let RenderCardOutput { qnodes, anodes, .. } = self.render_existing_card(card, false)?;
+        let RenderCardOutput { qnodes, anodes, .. } =
+            self.render_existing_card(card, false, false)?;
         Ok([
             rendered_nodes_to_record_field(&qnodes, with_html, false),
             rendered_nodes_to_record_field(&anodes, with_html, true),

rslib/src/notetype/render.rs

@@ -9,11 +9,12 @@ use super::Notetype;
 use super::NotetypeKind;
 use crate::prelude::*;
 use crate::template::field_is_empty;
-use crate::template::flatten_nodes;
 use crate::template::render_card;
 use crate::template::ParsedTemplate;
+use crate::template::RenderCardRequest;
 use crate::template::RenderedNode;
 
+#[derive(Debug)]
 pub struct RenderCardOutput {
     pub qnodes: Vec<RenderedNode>,
     pub anodes: Vec<RenderedNode>,
@@ -22,20 +23,31 @@ pub struct RenderCardOutput {
 }
 
 impl RenderCardOutput {
-    /// The question text, ignoring any unknown field replacements.
+    /// The question text. This is only valid to call when partial_render=false.
     pub fn question(&self) -> Cow<str> {
-        flatten_nodes(&self.qnodes)
+        match self.qnodes.as_slice() {
+            [RenderedNode::Text { text }] => text.into(),
+            _ => "not fully rendered".into(),
+        }
     }
 
-    /// The answer text, ignoring any unknown field replacements.
+    /// The answer text. This is only valid to call when partial_render=false.
     pub fn answer(&self) -> Cow<str> {
-        flatten_nodes(&self.anodes)
+        match self.anodes.as_slice() {
+            [RenderedNode::Text { text }] => text.into(),
+            _ => "not fully rendered".into(),
+        }
     }
 }
 
 impl Collection {
     /// Render an existing card saved in the database.
-    pub fn render_existing_card(&mut self, cid: CardId, browser: bool) -> Result<RenderCardOutput> {
+    pub fn render_existing_card(
+        &mut self,
+        cid: CardId,
+        browser: bool,
+        partial_render: bool,
+    ) -> Result<RenderCardOutput> {
         let card = self.storage.get_card(cid)?.or_invalid("no such card")?;
         let note = self
             .storage
@@ -50,7 +62,7 @@ impl Collection {
         }
         .or_invalid("missing template")?;
 
-        self.render_card(&note, &card, &nt, template, browser)
+        self.render_card(&note, &card, &nt, template, browser, partial_render)
     }
 
     /// Render a card that may not yet have been added.
@@ -62,6 +74,7 @@ impl Collection {
         template: &CardTemplate,
         card_ord: u16,
         fill_empty: bool,
+        partial_render: bool,
     ) -> Result<RenderCardOutput> {
         let card = self.existing_or_synthesized_card(note.id, template.ord, card_ord)?;
         let nt = self
@@ -72,7 +85,7 @@ impl Collection {
             fill_empty_fields(note, &template.config.q_format, &nt, &self.tr);
         }
 
-        self.render_card(note, &card, &nt, template, false)
+        self.render_card(note, &card, &nt, template, false, partial_render)
     }
 
     fn existing_or_synthesized_card(
@@ -102,6 +115,7 @@ impl Collection {
         nt: &Notetype,
         template: &CardTemplate,
         browser: bool,
+        partial_render: bool,
     ) -> Result<RenderCardOutput> {
         let mut field_map = note.fields_map(&nt.fields);
 
@@ -122,15 +136,16 @@ impl Collection {
             )
         };
 
-        let (qnodes, anodes) = render_card(
+        let (qnodes, anodes) = render_card(RenderCardRequest {
             qfmt,
             afmt,
-            &field_map,
-            card.template_idx,
-            nt.is_cloze(),
+            field_map: &field_map,
+            card_ord: card.template_idx,
+            is_cloze: nt.is_cloze(),
             browser,
-            &self.tr,
-        )?;
+            tr: &self.tr,
+            partial_render,
+        })?;
         Ok(RenderCardOutput {
             qnodes,
             anodes,
@@ -190,3 +205,30 @@ fn fill_empty_fields(note: &mut Note, qfmt: &str, nt: &Notetype, tr: &I18n) {
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::collection::CollectionBuilder;
+
+    #[test]
+    fn can_render_fully() -> Result<()> {
+        let mut col = CollectionBuilder::default().build()?;
+        let nt = col.get_notetype_by_name("Basic")?.unwrap();
+        let mut note = Note::new(&nt);
+        note.set_field(0, "front")?;
+        note.set_field(1, "back")?;
+        let out: RenderCardOutput =
+            col.render_uncommitted_card(&mut note, &nt.templates[0], 0, false, false)?;
+        assert_eq!(&out.question(), "front");
+        assert_eq!(&out.answer(), "front\n\n<hr id=answer>\n\nback");
+
+        // should work even if unknown filters are encountered
+        let mut tmpl = nt.templates[0].clone();
+        tmpl.config.q_format = "{{some_filter:Front}}".into();
+        let out = col.render_uncommitted_card(&mut note, &nt.templates[0], 0, false, false)?;
+        assert_eq!(&out.question(), "front");
+
+        Ok(())
+    }
+}

rslib/src/template.rs

@@ -22,6 +22,7 @@ use crate::cloze::add_cloze_numbers_in_string;
 use crate::error::AnkiError;
 use crate::error::Result;
 use crate::error::TemplateError;
+use crate::invalid_input;
 use crate::template_filters::apply_filters;
 
 pub type FieldMap<'a> = HashMap<&'a str, u16>;
@@ -387,8 +388,14 @@ pub enum RenderedNode {
 pub(crate) struct RenderContext<'a> {
     pub fields: &'a HashMap<&'a str, Cow<'a, str>>,
     pub nonempty_fields: &'a HashSet<&'a str>,
-    pub question_side: bool,
     pub card_ord: u16,
+    /// Should be set before rendering the answer, even if `partial_for_python`
+    /// is true.
+    pub frontside: Option<&'a str>,
+    /// If true, question/answer will not be fully rendered if an unknown filter
+    /// is encountered, and the frontend code will need to complete the
+    /// rendering.
+    pub partial_for_python: bool,
 }
 
 impl ParsedTemplate {
@@ -418,62 +425,75 @@ fn render_into(
                 append_str_to_nodes(rendered_nodes, text);
             }
             Replacement { key, .. } if key == "FrontSide" => {
-                // defer FrontSide rendering to Python, as extra
-                // filters may be required
-                rendered_nodes.push(RenderedNode::Replacement {
-                    field_name: (*key).to_string(),
-                    filters: vec![],
-                    current_text: "".into(),
-                });
-            }
-            Replacement { key, filters } if key.is_empty() && !filters.is_empty() => {
-                // if a filter is provided, we accept an empty field name to
-                // mean 'pass an empty string to the filter, and it will add
-                // its own text'
-                rendered_nodes.push(RenderedNode::Replacement {
-                    field_name: "".to_string(),
-                    current_text: "".to_string(),
-                    filters: filters.clone(),
-                })
+                if let Some(frontside) = &context.frontside {
+                    if context.partial_for_python {
+                        // defer FrontSide rendering to Python, as extra
+                        // filters may be required
+                        rendered_nodes.push(RenderedNode::Replacement {
+                            field_name: (*key).to_string(),
+                            filters: vec![],
+                            current_text: "".into(),
+                        });
+                    } else {
+                        append_str_to_nodes(rendered_nodes, frontside);
+                    }
+                } else {
+                    // Not valid on the question side
+                    return Err(TemplateError::FieldNotFound {
+                        field: "FrontSide".into(),
+                        filters: "".into(),
+                    });
+                }
             }
             Replacement { key, filters } => {
-                // apply built in filters if field exists
-                let (text, remaining_filters) = match context.fields.get(key.as_str()) {
-                    Some(text) => apply_filters(
-                        text,
-                        filters
-                            .iter()
-                            .map(|s| s.as_str())
-                            .collect::<Vec<_>>()
-                            .as_slice(),
-                        key,
-                        context,
-                    ),
-                    None => {
-                        // unknown field encountered
-                        let filters_str = filters
-                            .iter()
-                            .rev()
-                            .cloned()
-                            .chain(iter::once("".into()))
-                            .collect::<Vec<_>>()
-                            .join(":");
-                        return Err(TemplateError::FieldNotFound {
-                            field: (*key).to_string(),
-                            filters: filters_str,
+                if context.partial_for_python && key.is_empty() && !filters.is_empty() {
+                    // if a filter is provided, we accept an empty field name to
+                    // mean 'pass an empty string to the filter, and it will add
+                    // its own text'
+                    rendered_nodes.push(RenderedNode::Replacement {
+                        field_name: "".to_string(),
+                        current_text: "".to_string(),
+                        filters: filters.clone(),
+                    });
+                } else {
+                    // apply built in filters if field exists
+                    let (text, remaining_filters) = match context.fields.get(key.as_str()) {
+                        Some(text) => apply_filters(
+                            text,
+                            filters
+                                .iter()
+                                .map(|s| s.as_str())
+                                .collect::<Vec<_>>()
+                                .as_slice(),
+                            key,
+                            context,
+                        ),
+                        None => {
+                            // unknown field encountered
+                            let filters_str = filters
+                                .iter()
+                                .rev()
+                                .cloned()
+                                .chain(iter::once("".into()))
+                                .collect::<Vec<_>>()
+                                .join(":");
+                            return Err(TemplateError::FieldNotFound {
+                                field: (*key).to_string(),
+                                filters: filters_str,
+                            });
+                        }
+                    };
+
+                    // fully processed?
+                    if remaining_filters.is_empty() {
+                        append_str_to_nodes(rendered_nodes, text.as_ref())
+                    } else {
+                        rendered_nodes.push(RenderedNode::Replacement {
+                            field_name: (*key).to_string(),
+                            filters: remaining_filters,
+                            current_text: text.into(),
                         });
                     }
-                };
-
-                // fully processed?
-                if remaining_filters.is_empty() {
-                    append_str_to_nodes(rendered_nodes, text.as_ref())
-                } else {
-                    rendered_nodes.push(RenderedNode::Replacement {
-                        field_name: (*key).to_string(),
-                        filters: remaining_filters,
-                        current_text: text.into(),
-                    });
                 }
             }
             Conditional { key, children } => {
@@ -529,24 +549,6 @@ fn append_str_to_nodes(nodes: &mut Vec<RenderedNode>, text: &str) {
     }
 }
 
-/// Return the resolved text of a list of nodes, ignoring any unknown
-/// filters that were encountered.
-pub(crate) fn flatten_nodes(nodes: &[RenderedNode]) -> Cow<str> {
-    match nodes {
-        [RenderedNode::Text { text }] => text.into(),
-        nodes => {
-            let mut buf = String::new();
-            for node in nodes {
-                match node {
-                    RenderedNode::Text { text } => buf.push_str(text),
-                    RenderedNode::Replacement { current_text, .. } => buf.push_str(current_text),
-                }
-            }
-            buf.into()
-        }
-    }
-}
-
 /// True if provided text contains only whitespace and/or empty BR/DIV tags.
 pub(crate) fn field_is_empty(text: &str) -> bool {
     lazy_static! {
@@ -583,22 +585,36 @@ where
 // Rendering both sides
 //----------------------------------------
 
-#[allow(clippy::implicit_hasher)]
+pub struct RenderCardRequest<'a> {
+    pub qfmt: &'a str,
+    pub afmt: &'a str,
+    pub field_map: &'a HashMap<&'a str, Cow<'a, str>>,
+    pub card_ord: u16,
+    pub is_cloze: bool,
+    pub browser: bool,
+    pub tr: &'a I18n,
+    pub partial_render: bool,
+}
+
 pub fn render_card(
-    qfmt: &str,
-    afmt: &str,
-    field_map: &HashMap<&str, Cow<str>>,
-    card_ord: u16,
-    is_cloze: bool,
-    browser: bool,
-    tr: &I18n,
+    RenderCardRequest {
+        qfmt,
+        afmt,
+        field_map,
+        card_ord,
+        is_cloze,
+        browser,
+        tr,
+        partial_render: partial_for_python,
+    }: RenderCardRequest<'_>,
 ) -> Result<(Vec<RenderedNode>, Vec<RenderedNode>)> {
     // prepare context
     let mut context = RenderContext {
         fields: field_map,
         nonempty_fields: &nonempty_fields(field_map),
-        question_side: true,
+        frontside: None,
         card_ord,
+        partial_for_python,
     };
 
     // question side
@@ -630,7 +646,14 @@ pub fn render_card(
     }
 
     // answer side
-    context.question_side = false;
+    context.frontside = if context.partial_for_python {
+        Some("")
+    } else {
+        let Some(RenderedNode::Text {text }) = &qnodes.get(0) else {
+            invalid_input!("should not happen: first node not text");
+        };
+        Some(text)
+    };
     let anodes = ParsedTemplate::from_text(afmt)
         .and_then(|tmpl| tmpl.render(&context, tr))
         .map_err(|e| template_error_to_anki_error(e, false, browser, tr))?;
@@ -873,6 +896,7 @@ mod test {
     use crate::template::field_is_empty;
     use crate::template::nonempty_fields;
     use crate::template::FieldRequirements;
+    use crate::template::RenderCardRequest;
     use crate::template::RenderContext;
 
     #[test]
@@ -1081,8 +1105,9 @@ mod test {
         let ctx = RenderContext {
             fields: &map,
             nonempty_fields: &nonempty_fields(&map),
-            question_side: true,
+            frontside: None,
             card_ord: 1,
+            partial_for_python: true,
         };
 
         use crate::template::RenderedNode as FN;
@@ -1198,9 +1223,18 @@ mod test {
         let tr = I18n::template_only();
         use crate::template::RenderedNode as FN;
 
-        let qnodes = super::render_card("test{{E}}", "", &map, 1, false, false, &tr)
-            .unwrap()
-            .0;
+        let qnodes = super::render_card(RenderCardRequest {
+            qfmt: "test{{E}}",
+            afmt: "",
+            field_map: &map,
+            card_ord: 1,
+            is_cloze: false,
+            browser: false,
+            tr: &tr,
+            partial_render: true,
+        })
+        .unwrap()
+        .0;
         assert_eq!(
             qnodes[0],
             FN::Text {

rslib/src/template_filters.rs

@@ -19,8 +19,9 @@ use crate::text::strip_html;
 /// Applies built in filters, returning the resulting text and remaining
 /// filters.
 ///
-/// The first non-standard filter that is encountered will terminate processing,
-/// so non-standard filters must come at the end.
+/// If [context.partial_for_python] is true, the first non-standard filter that
+/// is encountered will terminate processing, so non-standard filters must come
+/// at the end. If false, missing filters are ignored.
 pub(crate) fn apply_filters<'a>(
     text: &'a str,
     filters: &[&str],
@@ -46,11 +47,14 @@ pub(crate) fn apply_filters<'a>(
                 text = output.into();
             }
             (false, _) => {
-                // unrecognized filter, return current text and remaining filters
-                return (
-                    text,
-                    filters.iter().skip(idx).map(ToString::to_string).collect(),
-                );
+                // unrecognized filter
+                if context.partial_for_python {
+                    //  return current text and remaining filters
+                    return (
+                        text,
+                        filters.iter().skip(idx).map(ToString::to_string).collect(),
+                    );
+                }
             }
         }
     }
@@ -236,8 +240,9 @@ field</a>
         let ctx = RenderContext {
             fields: &Default::default(),
             nonempty_fields: &Default::default(),
-            question_side: false,
+            frontside: Some(""),
             card_ord: 0,
+            partial_for_python: true,
         };
         assert_eq!(
             apply_filters("ignored", &["cloze", "type"], "Text", &ctx),
@@ -251,8 +256,9 @@ field</a>
         let mut ctx = RenderContext {
             fields: &Default::default(),
             nonempty_fields: &Default::default(),
-            question_side: true,
+            frontside: None,
             card_ord: 0,
+            partial_for_python: true,
         };
         assert_eq!(strip_html(&cloze_filter(text, &ctx)).as_ref(), "[...] two");
         assert_eq!(
@@ -263,7 +269,7 @@ field</a>
         ctx.card_ord = 1;
         assert_eq!(strip_html(&cloze_filter(text, &ctx)).as_ref(), "one [hint]");
 
-        ctx.question_side = false;
+        ctx.frontside = Some("");
         assert_eq!(strip_html(&cloze_filter(text, &ctx)).as_ref(), "one two");
 
         // if the provided ordinal did not match any cloze deletions,