refactor(server): map Lance errors by typed variant, not Display text

crates/lance-context-core/src/lib.rs

@@ -57,3 +57,7 @@ pub use store::{
 
 // Re-export CompactionMetrics from lance for Python bindings
 pub use lance::dataset::optimize::CompactionMetrics;
+
+// Re-export the Lance error type so downstream crates (e.g. the server) can
+// match on its typed variants instead of string-matching `Display` output.
+pub use lance::Error as LanceError;

crates/lance-context-server/src/error.rs

@@ -2,6 +2,7 @@ use axum::http::StatusCode;
 use axum::response::{IntoResponse, Response};
 use axum::Json;
 use lance_context_api::{ErrorBody, ErrorResponse};
+use lance_context_core::LanceError;
 
 #[derive(Debug)]
 pub enum AppError {
@@ -13,16 +14,31 @@ pub enum AppError {
 }
 
 impl AppError {
-    pub fn from_lance(err: impl std::fmt::Display) -> Self {
-        let msg = err.to_string();
-        if msg.contains("already in progress") {
-            AppError::CompactionInProgress
-        } else if msg.contains("not found") || msg.contains("DatasetNotFound") {
-            AppError::NotFound(msg)
-        } else if msg.contains("Invalid") {
-            AppError::InvalidRequest(msg)
-        } else {
-            AppError::Internal(msg)
+    /// Map a Lance error onto the API's error taxonomy.
+    ///
+    /// Prefers Lance's **typed** variants over string matching: `DatasetNotFound`
+    /// / `NotFound` → 404, `DatasetAlreadyExists` → 409, `InvalidInput` /
+    /// `SchemaMismatch` → 400. The one unavoidable string match is the
+    /// "compaction already in progress" signal, which the core raises as an
+    /// `ArrowError::InvalidArgumentError` that Lance folds into its generic
+    /// `Arrow` variant (no dedicated variant, see `store.rs`); it is checked
+    /// first so it still maps to 409 `COMPACTION_IN_PROGRESS`.
+    pub fn from_lance(err: LanceError) -> Self {
+        // Checked before the typed match: the compaction-in-progress signal is an
+        // Arrow-wrapped error with no dedicated variant, so only its text
+        // distinguishes it.
+        if err.to_string().contains("already in progress") {
+            return AppError::CompactionInProgress;
+        }
+        match err {
+            LanceError::DatasetNotFound { .. } | LanceError::NotFound { .. } => {
+                AppError::NotFound(err.to_string())
+            }
+            LanceError::DatasetAlreadyExists { .. } => AppError::AlreadyExists(err.to_string()),
+            LanceError::InvalidInput { .. } | LanceError::SchemaMismatch { .. } => {
+                AppError::InvalidRequest(err.to_string())
+            }
+            other => AppError::Internal(other.to_string()),
         }
     }
 }
@@ -51,3 +67,41 @@ impl IntoResponse for AppError {
         (status, Json(body)).into_response()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn maps_typed_variants_to_taxonomy() {
+        assert!(matches!(
+            AppError::from_lance(LanceError::dataset_not_found("db/x", "missing".into())),
+            AppError::NotFound(_)
+        ));
+        assert!(matches!(
+            AppError::from_lance(LanceError::dataset_already_exists("db/x")),
+            AppError::AlreadyExists(_)
+        ));
+        assert!(matches!(
+            AppError::from_lance(LanceError::invalid_input("bad field")),
+            AppError::InvalidRequest(_)
+        ));
+        assert!(matches!(
+            AppError::from_lance(LanceError::io("disk gone".to_string())),
+            AppError::Internal(_)
+        ));
+    }
+
+    #[test]
+    fn compaction_in_progress_is_detected_from_arrow_variant() {
+        // Reproduce how the core raises it: an ArrowError folded into Lance's
+        // generic `Arrow` variant (NOT `InvalidInput`), so only the text
+        // identifies it. `LanceError::arrow` is exactly what `From<ArrowError>`
+        // produces for a non-external ArrowError.
+        let err = LanceError::arrow("Compaction already in progress");
+        assert!(matches!(
+            AppError::from_lance(err),
+            AppError::CompactionInProgress
+        ));
+    }
+}