Use empty parsing context to build view's select in CREATE VIEW state…

…ment (#2049) (#2595)

Based on: #2049

KIKIMR-20891

CREATE VIEW statement parses (and validates) the select statement saved in the view. It should be parsed in a context isolated from the statements executed before the CREATE VIEW statement (we haven't decided yet on the exact scope of the context of the view's select statement, see [KIKIMR-20656](https://st.yandex-team.ru/KIKIMR-20656)). It is pretty obvious that one should be able to execute the following statement in one go ("one go" = one press of a "run" button in YDB UI):
```sql
-- create view NecessaryInnerView with (security_invoker = true) as select 1;
-- create view ContextTestingView with (security_invoker = true) as select * from `/local/NecessaryInnerView`; -- where `/local/...` is your cluster name

drop view ContextTestingView;
create view ContextTestingView with (security_invoker = true) as select * from `/local/NecessaryInnerView`;
```

However, executing both drop view and create view in one go currently produces and error:
```
DropObject is not yet implemented for intent determination transformer
```
which indicates that the context of the inner query:
```sql
select * from `/local/NecessaryInnerView`
```
is polluted by the previous:
```sql
drop view ContextTestingView;
```
statement.

This problem is fixed by using an empty parsing context for parsing view's inner select statement during handling of CREATE VIEW statement.

ydb/core/kqp/ut/view/view_ut.cpp

@@ -316,6 +316,24 @@ Y_UNIT_TEST_SUITE(TKQPViewTest) {
             UNIT_ASSERT(dropResult.GetIssues().ToString().Contains("Error: Path does not exist"));
         }
     }
+
+    Y_UNIT_TEST(ContextPollution) {
+        TKikimrRunner kikimr(TKikimrSettings().SetWithSampleTables(false));
+        EnableViewsFeatureFlag(kikimr);
+        auto session = kikimr.GetTableClient().CreateSession().GetValueSync().GetSession();
+
+        ExecuteDataDefinitionQuery(session, R"(
+            CREATE VIEW InnerView WITH (security_invoker = TRUE) AS SELECT 1;
+        )");
+        ExecuteDataDefinitionQuery(session, R"(
+            CREATE VIEW OuterView WITH (security_invoker = TRUE) AS SELECT * FROM InnerView;
+        )");
+
+        ExecuteDataDefinitionQuery(session, R"(
+            DROP VIEW OuterView;
+            CREATE VIEW OuterView WITH (security_invoker = TRUE) AS SELECT * FROM InnerView;
+        )");
+    }
 }
 
 Y_UNIT_TEST_SUITE(TSelectFromViewTest) {

ydb/library/yql/sql/v1/sql_translation.cpp

@@ -53,6 +53,33 @@ TString CollectTokens(const TRule_select_stmt& selectStatement) {
     return tokenCollector.Tokens;
 }
 
+NSQLTranslation::TTranslationSettings CreateViewTranslationSettings(const NSQLTranslation::TTranslationSettings& base) {
+    NSQLTranslation::TTranslationSettings settings;
+
+    settings.ClusterMapping = base.ClusterMapping;
+    settings.Mode = NSQLTranslation::ESqlMode::LIMITED_VIEW;
+
+    return settings;
+}
+
+TNodePtr BuildViewSelect(const TRule_select_stmt& query, TContext& ctx) {
+    const auto viewTranslationSettings = CreateViewTranslationSettings(ctx.Settings);
+    TContext viewParsingContext(viewTranslationSettings, {}, ctx.Issues);
+    TSqlSelect select(viewParsingContext, viewTranslationSettings.Mode);
+    TPosition pos;
+    auto source = select.Build(query, pos);
+    if (!source) {
+        return nullptr;
+    }
+    return BuildSelectResult(
+        pos,
+        std::move(source),
+        false,
+        false,
+        viewParsingContext.Scoped
+    );
+}
+
 }
 
 namespace NSQLTranslationV1 {
@@ -4484,19 +4511,11 @@ bool TSqlTranslation::ParseViewQuery(std::map<TString, TDeferredAtom>& features,
     const TString queryText = CollectTokens(query);
     features["query_text"] = {Ctx.Pos(), queryText};
 
-    {
-        TSqlSelect select(Ctx, Mode);
-        TPosition pos;
-        auto source = select.Build(query, pos);
-        if (!source) {
-            return false;
-        }
-        features["query_ast"] = {BuildSelectResult(pos,
-                                                   std::move(source),
-                                                   false,
-                                                   false,
-                                                   Ctx.Scoped), Ctx};
+    const auto viewSelect = BuildViewSelect(query, Ctx);
+    if (!viewSelect) {
+        return false;
     }
+    features["query_ast"] = {viewSelect, Ctx};
 
     return true;
 }