more useful template error message

pylib/anki/collection.py

@@ -672,7 +672,12 @@ where c.nid = n.id and c.id in %s group by nid"""
         (qfmt, afmt) = hooks.card_will_render((qfmt, afmt), fields, model, data)
 
         # render fields
+        try:
             qatext = render_card(self, qfmt, afmt, fields, card_ord)
+        except anki.rsbackend.BackendException as e:
+            errmsg = f"Card template has a problem:<br>{e}"
+            qatext = (errmsg, errmsg)
+
         ret: Dict[str, Any] = dict(q=qatext[0], a=qatext[1], id=card_id)
 
         # allow add-ons to modify the generated result

pylib/anki/rsbackend.py

@@ -23,7 +23,7 @@ class BackendException(Exception):
         if kind == "invalid_input":
             return f"invalid input: {err.invalid_input.info}"
         elif kind == "template_parse":
-            return f"template parse: {err.template_parse.info}"
+            return err.template_parse.info
         else:
             return f"unhandled error: {err}"
 

pylib/anki/template.py

@@ -44,7 +44,9 @@ def render_card(
     fields: Dict[str, str],
     card_ord: int,
 ) -> Tuple[str, str]:
-    "Renders the provided templates, returning rendered q & a text."
+    """Renders the provided templates, returning rendered q & a text.
+
+    Will raise if the template is invalid."""
     (qnodes, anodes) = col.backend.render_card(qfmt, afmt, fields, card_ord)
 
     qtext = apply_custom_filters(qnodes, fields, front_side=None)

rslib/src/backend.rs

@@ -97,7 +97,7 @@ impl Backend {
             Value::DeckTree(_) => todo!(),
             Value::FindCards(_) => todo!(),
             Value::BrowserRows(_) => todo!(),
-            Value::RenderCard(input) => OValue::RenderCard(self.render_template(input)),
+            Value::RenderCard(input) => OValue::RenderCard(self.render_template(input)?),
         })
     }
 
@@ -161,7 +161,7 @@ impl Backend {
         }
     }
 
-    fn render_template(&self, input: pt::RenderCardIn) -> pt::RenderCardOut {
+    fn render_template(&self, input: pt::RenderCardIn) -> Result<pt::RenderCardOut> {
         // convert string map to &str
         let fields: HashMap<_, _> = input
             .fields
@@ -175,13 +175,13 @@ impl Backend {
             &input.answer_template,
             &fields,
             input.card_ordinal as u16,
-        );
+        )?;
 
         // return
-        pt::RenderCardOut {
+        Ok(pt::RenderCardOut {
             question_nodes: rendered_nodes_to_proto(qnodes),
             answer_nodes: rendered_nodes_to_proto(anodes),
-        }
+        })
     }
 }
 

rslib/src/err.rs

@@ -16,11 +16,30 @@ pub enum AnkiError {
 
 // error helpers
 impl AnkiError {
-    pub(crate) fn parse<S: Into<String>>(s: S) -> AnkiError {
-        AnkiError::TemplateParseError { info: s.into() }
-    }
-
     pub(crate) fn invalid_input<S: Into<String>>(s: S) -> AnkiError {
         AnkiError::InvalidInput { info: s.into() }
     }
 }
+
+#[derive(Debug)]
+pub enum TemplateError {
+    NoClosingBrackets(String),
+    ConditionalNotClosed(String),
+    ConditionalNotOpen(String),
+}
+
+impl From<TemplateError> for AnkiError {
+    fn from(terr: TemplateError) -> Self {
+        AnkiError::TemplateParseError {
+            info: match terr {
+                TemplateError::NoClosingBrackets(context) => {
+                    format!("expected '{{{{field name}}}}', found '{}'", context)
+                }
+                TemplateError::ConditionalNotClosed(tag) => format!("missing '{{{{/{}}}}}'", tag),
+                TemplateError::ConditionalNotOpen(tag) => {
+                    format!("missing '{{{{#{}}}}}' or '{{{{^{}}}}}'", tag, tag)
+                }
+            },
+        }
+    }
+}

rslib/src/template.rs

@@ -1,7 +1,7 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-use crate::err::{AnkiError, Result};
+use crate::err::{Result, TemplateError};
 use crate::template_filters::apply_filters;
 use crate::text::strip_sounds;
 use lazy_static::lazy_static;
@@ -87,7 +87,7 @@ fn next_token(input: &str) -> nom::IResult<&str, Token> {
     alt((handle_token, text_token))(input)
 }
 
-fn tokens(template: &str) -> impl Iterator<Item = Result<Token>> {
+fn tokens(template: &str) -> impl Iterator<Item = std::result::Result<Token, TemplateError>> {
     let mut data = template;
 
     std::iter::from_fn(move || {
@@ -99,7 +99,7 @@ fn tokens(template: &str) -> impl Iterator<Item = Result<Token>> {
                 data = i;
                 Some(Ok(o))
             }
-            Err(e) => Some(Err(AnkiError::parse(format!("{:?}", e)))),
+            Err(_e) => Some(Err(TemplateError::NoClosingBrackets(data.to_string()))),
         }
     })
 }
@@ -132,16 +132,16 @@ impl ParsedTemplate<'_> {
     ///
     /// The legacy alternate syntax is not supported, so the provided text
     /// should be run through without_legacy_template_directives() first.
-    pub fn from_text(template: &str) -> Result<ParsedTemplate> {
+    pub fn from_text(template: &str) -> std::result::Result<ParsedTemplate, TemplateError> {
         let mut iter = tokens(template);
         Ok(Self(parse_inner(&mut iter, None)?))
     }
 }
 
-fn parse_inner<'a, I: Iterator<Item = Result<Token<'a>>>>(
+fn parse_inner<'a, I: Iterator<Item = std::result::Result<Token<'a>, TemplateError>>>(
     iter: &mut I,
     open_tag: Option<&'a str>,
-) -> Result<Vec<ParsedNode<'a>>> {
+) -> std::result::Result<Vec<ParsedNode<'a>>, TemplateError> {
     let mut nodes = vec![];
 
     while let Some(token) = iter.next() {
@@ -170,16 +170,13 @@ fn parse_inner<'a, I: Iterator<Item = Result<Token<'a>>>>(
                         return Ok(nodes);
                     }
                 }
-                return Err(AnkiError::parse(format!(
-                    "unbalanced closing tag: {:?} / {}",
-                    open_tag, t
-                )));
+                return Err(TemplateError::ConditionalNotOpen(t.to_string()));
             }
         });
     }
 
     if let Some(open) = open_tag {
-        Err(AnkiError::parse(format!("unclosed conditional {}", open)))
+        Err(TemplateError::ConditionalNotClosed(open.to_string()))
     } else {
         Ok(nodes)
     }
@@ -426,7 +423,7 @@ pub fn render_card(
     afmt: &str,
     field_map: &HashMap<&str, &str>,
     card_ord: u16,
-) -> (Vec<RenderedNode>, Vec<RenderedNode>) {
+) -> Result<(Vec<RenderedNode>, Vec<RenderedNode>)> {
     // prepare context
     let mut context = RenderContext {
         fields: field_map,
@@ -438,12 +435,7 @@ pub fn render_card(
 
     // question side
     let qnorm = without_legacy_template_directives(qfmt);
-    let qnodes = match ParsedTemplate::from_text(qnorm.as_ref()) {
-        Ok(tmpl) => tmpl.render(&context),
-        Err(e) => vec![RenderedNode::Text {
-            text: format!("{:?}", e),
-        }],
-    };
+    let qnodes = ParsedTemplate::from_text(qnorm.as_ref())?.render(&context);
 
     // if the question side didn't have any unknown filters, we can pass
     // FrontSide in now
@@ -454,14 +446,9 @@ pub fn render_card(
     // answer side
     context.question_side = false;
     let anorm = without_legacy_template_directives(afmt);
-    let anodes = match ParsedTemplate::from_text(anorm.as_ref()) {
-        Ok(tmpl) => tmpl.render(&context),
-        Err(e) => vec![RenderedNode::Text {
-            text: format!("{:?}", e),
-        }],
-    };
+    let anodes = ParsedTemplate::from_text(anorm.as_ref())?.render(&context);
 
-    (qnodes, anodes)
+    Ok((qnodes, anodes))
 }
 
 // Field requirements
@@ -779,7 +766,7 @@ mod test {
         let clozed_text = "{{c1::one}} {{c2::two::hint}}";
         let map: HashMap<_, _> = vec![("Text", clozed_text)].into_iter().collect();
 
-        let (qnodes, anodes) = render_card(fmt, fmt, &map, 0);
+        let (qnodes, anodes) = render_card(fmt, fmt, &map, 0).unwrap();
         assert_eq!(
             strip_html(get_complete_template(&qnodes).unwrap()),
             "[...] two"
@@ -790,11 +777,12 @@ mod test {
         );
 
         // FrontSide should render if only standard modifiers were used
-        let (_qnodes, anodes) = render_card("{{kana:text:Text}}", "{{FrontSide}}", &map, 1);
+        let (_qnodes, anodes) =
+            render_card("{{kana:text:Text}}", "{{FrontSide}}", &map, 1).unwrap();
         assert_eq!(get_complete_template(&anodes).unwrap(), clozed_text);
 
         // But if a custom modifier was used, it's deferred to the Python code
-        let (_qnodes, anodes) = render_card("{{custom:Text}}", "{{FrontSide}}", &map, 1);
+        let (_qnodes, anodes) = render_card("{{custom:Text}}", "{{FrontSide}}", &map, 1).unwrap();
         assert_eq!(get_complete_template(&anodes).is_none(), true)
     }
 }