Return docid in case of errors while rendering the document template

crates/milli/src/prompt/error.rs

@@ -38,6 +38,16 @@ pub struct RenderPromptError {
     pub fault: FaultSource,
 }
 impl RenderPromptError {
+    pub(crate) fn missing_context_with_external_docid(
+        external_docid: String,
+        inner: liquid::Error,
+    ) -> RenderPromptError {
+        Self {
+            kind: RenderPromptErrorKind::MissingContextWithExternalDocid(external_docid, inner),
+            fault: FaultSource::User,
+        }
+    }
+
     pub(crate) fn missing_context(inner: liquid::Error) -> RenderPromptError {
         Self { kind: RenderPromptErrorKind::MissingContext(inner), fault: FaultSource::User }
     }
@@ -47,6 +57,8 @@ impl RenderPromptError {
 pub enum RenderPromptErrorKind {
     #[error("missing field in document: {0}")]
     MissingContext(liquid::Error),
+    #[error("missing field in document `{0}`: {1}")]
+    MissingContextWithExternalDocid(String, liquid::Error),
 }
 
 impl From<RenderPromptError> for crate::Error {

crates/milli/src/prompt/mod.rs

@@ -119,6 +119,7 @@ impl Prompt {
         'doc: 'a, // lifetime of the allocator, will live for an entire chunk of documents
     >(
         &self,
+        external_docid: &str,
         document: impl crate::update::new::document::Document<'a> + Debug,
         field_id_map: &RefCell<GlobalFieldsIdsMap>,
         doc_alloc: &'doc Bump,
@@ -130,9 +131,12 @@ impl Prompt {
             self.max_bytes.unwrap_or_else(default_max_bytes).get(),
             doc_alloc,
         );
-        self.template
-            .render_to(&mut rendered, &context)
-            .map_err(RenderPromptError::missing_context)?;
+        self.template.render_to(&mut rendered, &context).map_err(|liquid_error| {
+            RenderPromptError::missing_context_with_external_docid(
+                external_docid.to_owned(),
+                liquid_error,
+            )
+        })?;
         Ok(std::str::from_utf8(rendered.into_bump_slice())
             .expect("render can only write UTF-8 because all inputs and processing preserve utf-8"))
     }