From 20319f797405e0527b39ee8b7edf8dbbac0aae21 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Renault?= <clement@meilisearch.com>
Date: Tue, 5 Nov 2019 12:02:42 +0100
Subject: [PATCH] Allow to introduce attributes only at the end of a schema

---
 meilidb-core/src/error.rs                | 6 +++---
 meilidb-core/src/update/schema_update.rs | 9 +++++++--
 meilidb-schema/src/lib.rs                | 4 ++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/meilidb-core/src/error.rs b/meilidb-core/src/error.rs
index 3fb4d199c..7d58e2756 100644
--- a/meilidb-core/src/error.rs
+++ b/meilidb-core/src/error.rs
@@ -97,7 +97,7 @@ pub enum UnsupportedOperation {
     SchemaAlreadyExists,
     CannotUpdateSchemaIdentifier,
     CannotReorderSchemaAttribute,
-    CannotIntroduceNewSchemaAttribute,
+    CanOnlyIntroduceNewSchemaAttributesAtEnd,
     CannotRemoveSchemaAttribute,
 }
 
@@ -108,8 +108,8 @@ impl fmt::Display for UnsupportedOperation {
             SchemaAlreadyExists => write!(f, "Cannot update index which already have a schema"),
             CannotUpdateSchemaIdentifier => write!(f, "Cannot update the identifier of a schema"),
             CannotReorderSchemaAttribute => write!(f, "Cannot reorder the attributes of a schema"),
-            CannotIntroduceNewSchemaAttribute => {
-                write!(f, "Cannot introduce new attributes in a schema")
+            CanOnlyIntroduceNewSchemaAttributesAtEnd => {
+                write!(f, "Can only introduce new attributes at end of a schema")
             }
             CannotRemoveSchemaAttribute => write!(f, "Cannot remove attributes from a schema"),
         }
diff --git a/meilidb-core/src/update/schema_update.rs b/meilidb-core/src/update/schema_update.rs
index 06f37b617..c033df6cf 100644
--- a/meilidb-core/src/update/schema_update.rs
+++ b/meilidb-core/src/update/schema_update.rs
@@ -14,7 +14,7 @@ pub fn apply_schema_update(
     docs_words_store: store::DocsWords,
 ) -> MResult<()> {
     use UnsupportedOperation::{
-        CannotIntroduceNewSchemaAttribute, CannotRemoveSchemaAttribute,
+        CanOnlyIntroduceNewSchemaAttributesAtEnd, CannotRemoveSchemaAttribute,
         CannotReorderSchemaAttribute, CannotUpdateSchemaIdentifier,
     };
 
@@ -33,7 +33,12 @@ pub fn apply_schema_update(
                         need_full_reindexing = true;
                     }
                 }
-                Diff::NewAttr { .. } => return Err(CannotIntroduceNewSchemaAttribute.into()),
+                Diff::NewAttr { pos, .. } => {
+                    // new attribute not at the end of the schema
+                    if pos < old_schema.number_of_attributes() {
+                        return Err(CanOnlyIntroduceNewSchemaAttributesAtEnd.into());
+                    }
+                }
                 Diff::RemovedAttr { .. } => return Err(CannotRemoveSchemaAttribute.into()),
             }
         }
diff --git a/meilidb-schema/src/lib.rs b/meilidb-schema/src/lib.rs
index 5ec64f3b6..929316d41 100644
--- a/meilidb-schema/src/lib.rs
+++ b/meilidb-schema/src/lib.rs
@@ -169,6 +169,10 @@ impl Schema {
         attributes
     }
 
+    pub fn number_of_attributes(&self) -> usize {
+        self.inner.attrs.len()
+    }
+
     pub fn props(&self, attr: SchemaAttr) -> SchemaProps {
         let (_, props) = self.inner.props[attr.0 as usize];
         props