YQL-19747: Hack parsing when at an empty id

There was a problem with parsing a query like
`SELECT # FROM t`, as it parsed `FROM` as if it
is an expeceted column name, so we failed to parse
a table name after `FROM` and therefore can not
complete column names, while the are so useful at
this position. Also this hack improved parsing
other queries, according to changed tests.
commit_hash:f5a657022a164d1d4bbf906db4bd2ad67bbcd956

4 files changed, 33 insertions, 3 deletions

diff --git a/yql/essentials/sql/v1/complete/analysis/global/global.cpp b/yql/essentials/sql/v1/complete/analysis/global/global.cpp
index 191814a8e55..555d5283c14 100644
--- a/yql/essentials/sql/v1/complete/analysis/global/global.cpp
+++ b/yql/essentials/sql/v1/complete/analysis/global/global.cpp
@@ -95,6 +95,17 @@ namespace NSQLComplete {
         }
 
         TGlobalContext Analyze(TCompletionInput input, TEnvironment env) override {
+            TString recovered;
+            if (IsRecoverable(input)) {
+                recovered = TString(input.Text);
+
+                // - "_" is to parse `SELECT x._ FROM table`
+                //        instead of `SELECT x.FROM table`
+                recovered.insert(input.CursorPosition, "_");
+
+                input.Text = recovered;
+            }
+
             SQLv1::Sql_queryContext* sqlQuery = Parse(input.Text);
             Y_ENSURE(sqlQuery);
 
@@ -114,6 +125,17 @@ namespace NSQLComplete {
         }
 
     private:
+        bool IsRecoverable(TCompletionInput input) const {
+            static const TStringBuf prev = " ";
+            static const TStringBuf next = " .(";
+
+            TStringBuf s = input.Text;
+            size_t i = input.CursorPosition;
+
+            return (i < s.size() && prev.Contains(s[i]) || i == s.size()) &&
+                   (i > 0 /*  */ && next.Contains(s[i - 1]));
+        }
+
         SQLv1::Sql_queryContext* Parse(TStringBuf input) {
             Chars_.load(input.Data(), input.Size(), /* lenient = */ false);
             Lexer_.reset();
diff --git a/yql/essentials/sql/v1/complete/analysis/global/global_ut.cpp b/yql/essentials/sql/v1/complete/analysis/global/global_ut.cpp
index 5e180fcb431..15aba3ee155 100644
--- a/yql/essentials/sql/v1/complete/analysis/global/global_ut.cpp
+++ b/yql/essentials/sql/v1/complete/analysis/global/global_ut.cpp
@@ -89,7 +89,7 @@ Y_UNIT_TEST_SUITE(GlobalAnalysisTests) {
         {
             TString query = "SELECT * FROM Concat(#";
             TGlobalContext ctx = global->Analyze(SharpedInput(query), {});
-            UNIT_ASSERT_VALUES_EQUAL(ctx.EnclosingFunction, Nothing());
+            UNIT_ASSERT_VALUES_EQUAL(ctx.EnclosingFunction, "Concat");
         }
         {
             TString query = "SELECT * FROM (#)";
diff --git a/yql/essentials/sql/v1/complete/analysis/global/named_node.cpp b/yql/essentials/sql/v1/complete/analysis/global/named_node.cpp
index 14b928c53e5..0896b508432 100644
--- a/yql/essentials/sql/v1/complete/analysis/global/named_node.cpp
+++ b/yql/essentials/sql/v1/complete/analysis/global/named_node.cpp
@@ -84,6 +84,10 @@ namespace NSQLComplete {
             }
 
             std::any visitBind_parameter(SQLv1::Bind_parameterContext* ctx) override {
+                if (IsEnclosing(ctx)) {
+                    return {};
+                }
+
                 TMaybe<std::string> id = GetId(ctx);
                 if (id.Empty() || id == "_") {
                     return {};
diff --git a/yql/essentials/sql/v1/complete/sql_complete_ut.cpp b/yql/essentials/sql/v1/complete/sql_complete_ut.cpp
index 5b99c6a3fe1..aa955bc2cc5 100644
--- a/yql/essentials/sql/v1/complete/sql_complete_ut.cpp
+++ b/yql/essentials/sql/v1/complete/sql_complete_ut.cpp
@@ -905,6 +905,7 @@ Y_UNIT_TEST_SUITE(SqlCompleteTests) {
         auto engine = MakeSqlCompletionEngineUT();
         {
             TVector<TCandidate> expected = {
+                {BindingName, "$udf"},
                 {HintName, "XLOCK"},
             };
             UNIT_ASSERT_VALUES_EQUAL(Complete(engine, "PROCESS my_table USING $udf(TableRows()) WITH "), expected);
@@ -1105,8 +1106,11 @@ Y_UNIT_TEST_SUITE(SqlCompleteTests) {
             };
             UNIT_ASSERT_VALUES_EQUAL(CompleteTop(2, engine, "SELECT # FROM example.`/people` AS x"), expected);
         }
-        { // It is parsed into ``` SELECT x.FROM example.`/people` AS x ```
-            TVector<TCandidate> expected = {};
+        {
+            TVector<TCandidate> expected = {
+                {ColumnName, "Age"},
+                {ColumnName, "Name"},
+            };
             UNIT_ASSERT_VALUES_EQUAL(CompleteTop(2, engine, "SELECT x.# FROM example.`/people` AS x"), expected);
         }
         {