sql: no-op SHOW SYNTAX in replication mode

Currently on the CLI, the command must parse on the server for it to
run. For replication related commands, we have not implemented `SHOW
SYNTAX` yet. This is a bit of effort and seems outside the scope of what
we want for now.

For now, handle replication commands by no-oping them.

Release note: None

Author: otan

pkg/cli/interactive_tests/test_replication_protocol.tcl

@@ -0,0 +1,20 @@
+#! /usr/bin/env expect -f
+
+source [file join [file dirname $argv0] common.tcl]
+
+start_server $argv
+
+start_test "Ensure that replication mode works as expected in the sql shell"
+
+# Spawn a sql shell.
+spawn /bin/bash
+
+send "$argv sql --url `cat server_url`'\&replication=database' -e 'IDENTIFY_SYSTEM'\r"
+eexpect "(1 row)"
+
+send_eof
+eexpect eof
+
+end_test
+
+stop_server $argv

pkg/sql/delegate/BUILD.bazel

@@ -53,13 +53,15 @@ go_library(
         "//pkg/sql/oidext",
         "//pkg/sql/opt/cat",
         "//pkg/sql/parser",
+        "//pkg/sql/pgrepl/pgreplparser",
         "//pkg/sql/pgwire/pgcode",
         "//pkg/sql/pgwire/pgerror",
         "//pkg/sql/privilege",
         "//pkg/sql/roleoption",
         "//pkg/sql/sem/catconstants",
         "//pkg/sql/sem/eval",
         "//pkg/sql/sem/tree",
+        "//pkg/sql/sessiondatapb",
         "//pkg/sql/sqlerrors",
         "//pkg/sql/sqltelemetry",
         "//pkg/sql/syntheticprivilege",

pkg/sql/delegate/show_syntax.go

@@ -18,7 +18,9 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/colinfo"
 	"github.com/cockroachdb/cockroach/pkg/sql/lexbase"
 	"github.com/cockroachdb/cockroach/pkg/sql/parser"
+	"github.com/cockroachdb/cockroach/pkg/sql/pgrepl/pgreplparser"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
+	"github.com/cockroachdb/cockroach/pkg/sql/sessiondatapb"
 )
 
 // delegateShowSyntax implements SHOW SYNTAX. This statement is usually handled
@@ -41,6 +43,16 @@ func (d *delegator) delegateShowSyntax(n *tree.ShowSyntax) (tree.Statement, erro
 		colinfo.ShowSyntaxColumns[0].Name, colinfo.ShowSyntaxColumns[1].Name,
 	)
 
+	// For replication based statements, return nothing for now.
+	if d.evalCtx.SessionData().ReplicationMode != sessiondatapb.ReplicationMode_REPLICATION_MODE_DISABLED &&
+		pgreplparser.IsReplicationProtocolCommand(n.Statement) {
+		return d.parse(fmt.Sprintf(
+			`SELECT '' AS %s, '' AS %s FROM generate_series(0, -1) x`,
+			colinfo.ShowSyntaxColumns[0].Name,
+			colinfo.ShowSyntaxColumns[1].Name,
+		))
+	}
+
 	comma := ""
 	// TODO(knz): in the call below, reportErr is nil although we might
 	// want to be able to capture (and report) these errors as well.