Emit better error messages when parsing vectors

crates/milli/src/vector/parsed_vectors.rs

@@ -19,10 +19,54 @@ pub enum RawVectors<'doc> {
     ImplicitlyUserProvided(#[serde(borrow)] Option<&'doc RawValue>),
 }
 
+pub enum RawVectorsError {
+    DeserializeSeq { index: usize, error: String },
+    DeserializeKey { error: String },
+    DeserializeRegenerate { error: String },
+    DeserializeEmbeddings { error: String },
+    UnknownField { field: String },
+    MissingRegenerate,
+    WrongKind { kind: &'static str, value: String },
+    Parsing(serde_json::Error),
+}
+
+impl RawVectorsError {
+    pub fn msg(self, embedder_name: &str) -> String {
+        match self {
+            RawVectorsError::DeserializeSeq { index, error } => format!(
+                "Could not parse `._vectors.{embedder_name}[{index}]`: {error}"
+            ),
+            RawVectorsError::DeserializeKey { error } => format!(
+                "Could not parse a field at `._vectors.{embedder_name}`: {error}"
+            ),
+            RawVectorsError::DeserializeRegenerate { error } => format!(
+                "Could not parse `._vectors.{embedder_name}.regenerate`: {error}"
+            ),
+            RawVectorsError::DeserializeEmbeddings { error } => format!(
+                "Could not parse `._vectors.{embedder_name}.embeddings`: {error}"
+            ),
+            RawVectorsError::UnknownField { field } => format!(
+                "Unexpected field `._vectors.{embedder_name}.{field}`\n \
+                \t - note: the allowed fields are `regenerate` and `embeddings`"
+            ),
+            RawVectorsError::MissingRegenerate => format!(
+                "Missing field `._vectors.{embedder_name}.regenerate`\n \
+                \t - note: `._vectors.{embedder_name}` must be an array of floats, an array of arrays of floats, or an object with field `regenerate`"
+            ),
+            RawVectorsError::WrongKind { kind, value } => format!(
+                "Expected `._vectors.{embedder_name}` to be an array of floats, an array of arrays of floats, or an object with at least the field `regenerate`, but got the {kind} `{value}`"
+            ),
+            RawVectorsError::Parsing(error) => format!(
+                "Could not parse `._vectors.{embedder_name}`: {error}"
+            ),
+        }
+    }
+}
+
 impl<'doc> RawVectors<'doc> {
-    pub fn from_raw_value(raw: &'doc RawValue) -> Result<Self, serde_json::Error> {
+    pub fn from_raw_value(raw: &'doc RawValue) -> Result<Self, RawVectorsError> {
         use serde::de::Deserializer as _;
-        Ok(match raw.deserialize_any(RawVectorsVisitor)? {
+        Ok(match raw.deserialize_any(RawVectorsVisitor).map_err(RawVectorsError::Parsing)?? {
             RawVectorsVisitorValue::ImplicitNone => RawVectors::ImplicitlyUserProvided(None),
             RawVectorsVisitorValue::Implicit => RawVectors::ImplicitlyUserProvided(Some(raw)),
             RawVectorsVisitorValue::Explicit { regenerate, embeddings } => {
@@ -41,7 +85,7 @@ enum RawVectorsVisitorValue<'doc> {
 }
 
 impl<'doc> serde::de::Visitor<'doc> for RawVectorsVisitor {
-    type Value = RawVectorsVisitorValue<'doc>;
+    type Value = std::result::Result<RawVectorsVisitorValue<'doc>, RawVectorsError>;
 
     fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
         write!(formatter, "a map containing at least `regenerate`, or an array of floats`")
@@ -51,7 +95,7 @@ impl<'doc> serde::de::Visitor<'doc> for RawVectorsVisitor {
     where
         E: serde::de::Error,
     {
-        Ok(RawVectorsVisitorValue::ImplicitNone)
+        Ok(Ok(RawVectorsVisitorValue::ImplicitNone))
     }
 
     fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
@@ -65,42 +109,150 @@ impl<'doc> serde::de::Visitor<'doc> for RawVectorsVisitor {
     where
         E: serde::de::Error,
     {
-        Ok(RawVectorsVisitorValue::ImplicitNone)
+        Ok(Ok(RawVectorsVisitorValue::ImplicitNone))
     }
 
     fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
     where
         A: serde::de::SeqAccess<'doc>,
     {
+        let mut index = 0;
         // must consume all elements or parsing fails
-        while let Some(_) = seq.next_element::<&RawValue>()? {}
-        Ok(RawVectorsVisitorValue::Implicit)
+        loop {
+            match seq.next_element::<&RawValue>() {
+                Ok(Some(_)) => index += 1,
+                Err(error) => {
+                    return Ok(Err(RawVectorsError::DeserializeSeq {
+                        index,
+                        error: error.to_string(),
+                    }))
+                }
+                Ok(None) => break,
+            };
+        }
+        Ok(Ok(RawVectorsVisitorValue::Implicit))
     }
 
     fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
     where
         A: serde::de::MapAccess<'doc>,
     {
-        use serde::de::Error as _;
         let mut regenerate = None;
         let mut embeddings = None;
-        while let Some(s) = map.next_key()? {
-            match s {
-                "regenerate" => {
-                    let value: bool = map.next_value()?;
+        loop {
+            match map.next_key::<&str>() {
+                Ok(Some("regenerate")) => {
+                    let value: bool = match map.next_value() {
+                        Ok(value) => value,
+                        Err(error) => {
+                            return Ok(Err(RawVectorsError::DeserializeRegenerate {
+                                error: error.to_string(),
+                            }))
+                        }
+                    };
                     regenerate = Some(value);
                 }
-                "embeddings" => {
-                    let value: &RawValue = map.next_value()?;
+                Ok(Some("embeddings")) => {
+                    let value: &RawValue = match map.next_value() {
+                        Ok(value) => value,
+                        Err(error) => {
+                            return Ok(Err(RawVectorsError::DeserializeEmbeddings {
+                                error: error.to_string(),
+                            }))
+                        }
+                    };
                     embeddings = Some(value);
                 }
-                other => return Err(A::Error::unknown_field(other, &["regenerate", "embeddings"])),
+                Ok(Some(other)) => {
+                    return Ok(Err(RawVectorsError::UnknownField { field: other.to_string() }))
+                }
+                Ok(None) => break,
+                Err(error) => {
+                    return Ok(Err(RawVectorsError::DeserializeKey { error: error.to_string() }))
+                }
             }
         }
         let Some(regenerate) = regenerate else {
-            return Err(A::Error::missing_field("regenerate"));
+            return Ok(Err(RawVectorsError::MissingRegenerate));
         };
-        Ok(RawVectorsVisitorValue::Explicit { regenerate, embeddings })
+        Ok(Ok(RawVectorsVisitorValue::Explicit { regenerate, embeddings }))
+    }
+
+    fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "boolean", value: v.to_string() }))
+    }
+
+    fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "integer", value: v.to_string() }))
+    }
+
+    fn visit_i128<E>(self, v: i128) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "integer", value: v.to_string() }))
+    }
+
+    fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "integer", value: v.to_string() }))
+    }
+
+    fn visit_u128<E>(self, v: u128) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "integer", value: v.to_string() }))
+    }
+
+    fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "number", value: v.to_string() }))
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "string", value: v.to_string() }))
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "string", value: v }))
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "bytes", value: format!("{v:?}") }))
+    }
+
+    fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: serde::Deserializer<'doc>,
+    {
+        deserializer.deserialize_any(self)
+    }
+
+    fn visit_enum<A>(self, _data: A) -> Result<Self::Value, A::Error>
+    where
+        A: serde::de::EnumAccess<'doc>,
+    {
+        Ok(Err(RawVectorsError::WrongKind { kind: "enum", value: "a variant".to_string() }))
     }
 }