sql: enable_replacement_materialized_views feature flag

This commit adds a feature flag to gate the creation and application of
replacement materialized views. It's disabled by default and enabled in
CI.

Author: teskje

misc/python/materialize/mzcompose/__init__.py

@@ -106,6 +106,7 @@ def get_minimal_system_parameters(
         "enable_rbac_checks": "true",
         "enable_reduce_mfp_fusion": "true",
         "enable_refresh_every_mvs": "true",
+        "enable_replacement_materialized_views": "true",
         "enable_repr_typecheck": "true",
         "enable_cluster_schedule_refresh": "true",
         "enable_sql_server_source": "true",

src/sql/src/plan/statement/ddl.rs

@@ -2735,6 +2735,8 @@ pub fn plan_create_materialized_view(
 
     // Validate the replacement target, if one is given.
     let replacement_target = if let Some(target_name) = &stmt.replacing {
+        scx.require_feature_flag(&vars::ENABLE_REPLACEMENT_MATERIALIZED_VIEWS)?;
+
         let target = scx.get_item_by_resolved_name(target_name)?;
         if target.item_type() != CatalogItemType::MaterializedView {
             return Err(PlanError::InvalidReplacement {
@@ -7373,6 +7375,8 @@ pub fn plan_alter_materialized_view_apply_replacement(
         replacement_name,
     } = stmt;
 
+    scx.require_feature_flag(&vars::ENABLE_REPLACEMENT_MATERIALIZED_VIEWS)?;
+
     let object_type = ObjectType::MaterializedView;
     let Some(mv) = resolve_item_or_type(scx, object_type, name.clone(), if_exists)? else {
         scx.catalog.add_notice(PlanNotice::ObjectDoesNotExist {

src/sql/src/session/vars/definitions.rs

@@ -2230,6 +2230,12 @@ feature_flags!(
         default: false,
         enable_for_item_parsing: false,
     },
+    {
+        name: enable_replacement_materialized_views,
+        desc: "Whether to enable replacement materialized views.",
+        default: false,
+        enable_for_item_parsing: true,
+    },
 );
 
 impl From<&super::SystemVars> for OptimizerFeatures {