Rejecting redundant options in Create Collation

[Daniel Verite]

  Hi,

Currently, it's not an error for CREATE COLLATION to be invoked
with options repeated several times. The last (rightmost) value is kept
and the others are lost.
For instance CREATE COLLATION x (lc_ctype='en_US.UTF8',
lc_collate='en_US.UTF8', lc_ctype='C')
silently ignores lc_ctype='en_US.UTF8'. But that kind of invocation
isn't likely to be legit. It's more plausible that it's the result of
some mistake or confusion.
The same goes for the other options:

CREATE COLLATION [ IF NOT EXISTS ] name (
    [ LOCALE = locale, ]
    [ LC_COLLATE = lc_collate, ]
    [ LC_CTYPE = lc_ctype, ]
    [ PROVIDER = provider, ]
    [ DETERMINISTIC = boolean, ]
    [ VERSION = version ]
)

I suggest the attached simple patch to raise an error when any of
these options is specified multiple times.


Best regards,
-- 
Daniel Vérité
PostgreSQL-powered mailer: https://www.manitou-mail.org
Twitter: @DanielVerite

diff --git a/src/backend/commands/collationcmds.c 
b/src/backend/commands/collationcmds.c
index 9f6582c530..7dfd544396 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -108,6 +108,19 @@ DefineCollation(ParseState *pstate, List *names, List 
*parameters, bool if_not_e
                        break;
                }
 
+               if (*defelp != NULL)
+               {
+                       /*
+                        * If the option was previously set, it means that it 
occurs
+                        * several times in the list, which is not allowed.
+                        */
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_SYNTAX_ERROR),
+                                        errmsg("conflicting or redundant 
options",
+                                                       defel->defname),
+                                        parser_errposition(pstate, 
defel->location)));
+                       break;
+               }
                *defelp = defel;
        }