clearer error when closing tags transposed

rslib/src/err.rs

@@ -25,8 +25,14 @@ impl AnkiError {
 pub enum TemplateError {
     NoClosingBrackets(String),
     ConditionalNotClosed(String),
-    ConditionalNotOpen(String),
+    ConditionalNotOpen {
-    FieldNotFound { filters: String, field: String },
+        closed: String,
+        currently_open: Option<String>,
+    },
+    FieldNotFound {
+        filters: String,
+        field: String,
+    },
 }
 
 impl From<TemplateError> for AnkiError {
@@ -37,8 +43,18 @@ impl From<TemplateError> for AnkiError {
                     format!("missing '}}}}' in '{}'", context)
                 }
                 TemplateError::ConditionalNotClosed(tag) => format!("missing '{{{{/{}}}}}'", tag),
-                TemplateError::ConditionalNotOpen(tag) => {
+                TemplateError::ConditionalNotOpen {
-                    format!("missing '{{{{#{}}}}}' or '{{{{^{}}}}}'", tag, tag)
+                    closed,
+                    currently_open,
+                } => {
+                    if let Some(open) = currently_open {
+                        format!("Found {{{{/{}}}}}, but expected {{{{/{}}}}}", closed, open)
+                    } else {
+                        format!(
+                            "Found {{{{/{}}}}}, but missing '{{{{#{}}}}}' or '{{{{^{}}}}}'",
+                            closed, closed, closed
+                        )
+                    }
                 }
                 TemplateError::FieldNotFound { field, filters } => format!(
                     "found '{{{{{}{}}}}}', but there is no field called '{}'",

rslib/src/template.rs

@@ -164,13 +164,20 @@ fn parse_inner<'a, I: Iterator<Item = TemplateResult<Token<'a>>>>(
                 children: parse_inner(iter, Some(t))?,
             },
             CloseConditional(t) => {
-                if let Some(open) = open_tag {
+                let currently_open = if let Some(open) = open_tag {
                     if open == t {
                         // matching closing tag, move back to parent
                         return Ok(nodes);
+                    } else {
+                        Some(open.to_string())
                     }
-                }
+                } else {
-                return Err(TemplateError::ConditionalNotOpen(t.to_string()));
+                    None
+                };
+                return Err(TemplateError::ConditionalNotOpen {
+                    closed: t.to_string(),
+                    currently_open,
+                });
             }
         });
     }