Fix leaks in load_domaintype_info().

load_domaintype_info() intentionally leaks some intermediate cruft
into the long-lived DomainConstraintCache's memory context, reasoning
that the amount of leakage will typically not be much so it's not
worth doing a copyObject() of the final tree to avoid that.  But
Valgrind knows nothing of engineering tradeoffs and complains anyway.

On the whole, the copyObject doesn't cost that much and this is
surely not a performance-critical code path, so let's do it the
clean way.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/285483.1746756246@sss.pgh.pa.us

Author: tglsfdc

src/backend/utils/cache/typcache.c

@@ -1171,9 +1171,6 @@ load_domaintype_info(TypeCacheEntry *typentry)
 				elog(ERROR, "domain \"%s\" constraint \"%s\" has NULL conbin",
 					 NameStr(typTup->typname), NameStr(c->conname));
 
-			/* Convert conbin to C string in caller context */
-			constring = TextDatumGetCString(val);
-
 			/* Create the DomainConstraintCache object and context if needed */
 			if (dcc == NULL)
 			{
@@ -1189,9 +1186,8 @@ load_domaintype_info(TypeCacheEntry *typentry)
 				dcc->dccRefCount = 0;
 			}
 
-			/* Create node trees in DomainConstraintCache's context */
-			oldcxt = MemoryContextSwitchTo(dcc->dccContext);
-
+			/* Convert conbin to a node tree, still in caller's context */
+			constring = TextDatumGetCString(val);
 			check_expr = (Expr *) stringToNode(constring);
 
 			/*
@@ -1206,10 +1202,13 @@ load_domaintype_info(TypeCacheEntry *typentry)
 			 */
 			check_expr = expression_planner(check_expr);
 
+			/* Create only the minimally needed stuff in dccContext */
+			oldcxt = MemoryContextSwitchTo(dcc->dccContext);
+
 			r = makeNode(DomainConstraintState);
 			r->constrainttype = DOM_CONSTRAINT_CHECK;
 			r->name = pstrdup(NameStr(c->conname));
-			r->check_expr = check_expr;
+			r->check_expr = copyObject(check_expr);
 			r->check_exprstate = NULL;
 
 			MemoryContextSwitchTo(oldcxt);