Cherry-pick da594ae with conflicts

go/vt/vtgate/planbuilder/testdata/other_read_cases.json

@@ -87,5 +87,26 @@
         "SingleShardOnly": true
       }
     }
+  },
+  {
+    "comment": "describe info_schema table",
+    "query": "describe information_schema.administrable_role_authorizations",
+    "plan": {
+      "QueryType": "EXPLAIN",
+      "Original": "describe information_schema.administrable_role_authorizations",
+      "Instructions": {
+        "OperatorType": "Send",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": "AnyShard()",
+        "Query": "explain information_schema.administrable_role_authorizations",
+        "SingleShardOnly": true
+      },
+      "TablesUsed": [
+        "main.administrable_role_authorizations"
+      ]
+    }
   }
 ]

go/vt/vtgate/planbuilder/vexplain.go

@@ -23,6 +23,8 @@ import (
 
 	"vitess.io/vitess/go/vt/vtgate/planbuilder/plancontext"
 
+	"vitess.io/vitess/go/vt/vtgate/vindexes"
+
 	"vitess.io/vitess/go/sqltypes"
 	"vitess.io/vitess/go/vt/key"
 	querypb "vitess.io/vitess/go/vt/proto/query"
@@ -63,24 +65,37 @@ func buildVExplainPlan(ctx context.Context, vexplainStmt *sqlparser.VExplainStmt
 }
 
 func explainTabPlan(explain *sqlparser.ExplainTab, vschema plancontext.VSchema) (*planResult, error) {
-	_, _, ks, _, destination, err := vschema.FindTableOrVindex(explain.Table)
-	if err != nil {
-		return nil, err
+	var keyspace *vindexes.Keyspace
+	var destination key.Destination
+
+	if sqlparser.SystemSchema(explain.Table.Qualifier.String()) {
+		var err error
+		keyspace, err = vschema.AnyKeyspace()
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		var err error
+		var ks string
+		_, _, ks, _, destination, err = vschema.FindTableOrVindex(explain.Table)
+		if err != nil {
+			return nil, err
+		}
+		explain.Table.Qualifier = sqlparser.NewIdentifierCS("")
+
+		keyspace, err = vschema.FindKeyspace(ks)
+		if err != nil {
+			return nil, err
+		}
+		if keyspace == nil {
+			return nil, vterrors.VT14004(ks)
+		}
 	}
-	explain.Table.Qualifier = sqlparser.NewIdentifierCS("")
 
 	if destination == nil {
 		destination = key.DestinationAnyShard{}
 	}
 
-	keyspace, err := vschema.FindKeyspace(ks)
-	if err != nil {
-		return nil, err
-	}
-	if keyspace == nil {
-		return nil, vterrors.VT14004(ks)
-	}
-
 	return newPlanResult(&engine.Send{
 		Keyspace:          keyspace,
 		TargetDestination: destination,
@@ -126,3 +141,54 @@ func buildVExplainLoggingPlan(ctx context.Context, explain *sqlparser.VExplainSt
 
 	return &planResult{primitive: &engine.VExplain{Input: input.primitive, Type: explain.Type}, tables: input.tables}, nil
 }
+<<<<<<< HEAD
+=======
+
+// buildExplainStmtPlan takes an EXPLAIN query and if possible sends the whole query to a single shard
+func buildExplainStmtPlan(stmt sqlparser.Statement, reservedVars *sqlparser.ReservedVars, vschema plancontext.VSchema) (*planResult, error) {
+	explain := stmt.(*sqlparser.ExplainStmt)
+	switch explain.Statement.(type) {
+	case sqlparser.SelectStatement, *sqlparser.Update, *sqlparser.Delete, *sqlparser.Insert:
+		return explainPlan(explain, reservedVars, vschema)
+	default:
+		return buildOtherReadAndAdmin(sqlparser.String(explain), vschema)
+	}
+}
+
+func explainPlan(explain *sqlparser.ExplainStmt, reservedVars *sqlparser.ReservedVars, vschema plancontext.VSchema) (*planResult, error) {
+	ctx, err := plancontext.CreatePlanningContext(explain.Statement, reservedVars, vschema, Gen4)
+	if err != nil {
+		return nil, err
+	}
+
+	ks := ctx.SemTable.SingleKeyspace()
+	if ks == nil {
+		return nil, vterrors.VT03031()
+	}
+
+	if err = queryRewrite(ctx, explain.Statement); err != nil {
+		return nil, err
+	}
+
+	// Remove keyspace qualifier from columns and tables.
+	sqlparser.RemoveKeyspace(explain.Statement)
+
+	var tables []string
+	for _, table := range ctx.SemTable.Tables {
+		name, err := table.Name()
+		if err != nil {
+			// this is just for reporting which tables we are touching
+			// it's OK to ignore errors here
+			continue
+		}
+		tables = append(tables, operators.QualifiedString(ks, name.Name.String()))
+	}
+
+	return newPlanResult(&engine.Send{
+		Keyspace:          ks,
+		TargetDestination: key.DestinationAnyShard{},
+		Query:             sqlparser.String(explain),
+		SingleShardOnly:   true,
+	}, tables...), nil
+}
+>>>>>>> da594ae738 (fix: handle info_schema routing (#15899))