Replace run-time error check with assertion

[Peter Eisentraut]

In the attached patch, the error message was checking that the 
structures returned from the parser matched expectations.  That's 
something we usually use assertions for, not a full user-facing error 
message.  So I replaced that with an assertion (hidden inside 
lfirst_node()).
From a30697758c475db2f4333cedbe6aad1e1acd0ee8 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Tue, 25 May 2021 11:27:04 +0200
Subject: [PATCH] Replace run-time error check with assertion
The error message was checking that the structures returned from the
parser matched expectations.  That's something we usually use
assertions for, not a full user-facing error message.
---
 src/backend/commands/statscmds.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
index acae19176c..b244a0fbd7 100644
--- a/src/backend/commands/statscmds.c
+++ b/src/backend/commands/statscmds.c
@@ -220,26 +220,14 @@ CreateStatistics(CreateStatsStmt *stmt)
         */
        foreach(cell, stmt->exprs)
        {
-               Node       *expr = (Node *) lfirst(cell);
-               StatsElem  *selem;
-               HeapTuple       atttuple;
-               Form_pg_attribute attForm;
-               TypeCacheEntry *type;
-
-               /*
-                * We should not get anything else than StatsElem, given the 
grammar.
-                * But let's keep it as a safety.
-                */
-               if (!IsA(expr, StatsElem))
-                       ereport(ERROR,
-                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-                                        errmsg("only simple column references 
and expressions are allowed in CREATE STATISTICS")));
-
-               selem = (StatsElem *) expr;
+               StatsElem  *selem = lfirst_node(StatsElem, cell);
 
                if (selem->name)                /* column reference */
                {
                        char       *attname;
+                       HeapTuple       atttuple;
+                       Form_pg_attribute attForm;
+                       TypeCacheEntry *type;
 
                        attname = selem->name;
 
@@ -273,6 +261,7 @@ CreateStatistics(CreateStatsStmt *stmt)
                {
                        Node       *expr = selem->expr;
                        Oid                     atttype;
+                       TypeCacheEntry *type;
 
                        Assert(expr != NULL);
 
-- 
2.31.1