In COPY FROM, fail cleanly when unsupported encoding conversion is needed.

In recent releases, such cases fail with "cache lookup failed for
function 0" rather than complaining that the conversion function
doesn't exist as prior versions did.  Seems to be a consequence of
sloppy refactoring in commit f82de5c46.  Add the missing error check.

Per report from Pierre Fortin.  Back-patch to v14 where the
oversight crept in.

Discussion: https://postgr.es/m/20230929163739.3bea46e5.pfortin@pfortin.com

diff --git a/src/backend/commands/copyfrom.c b/src/backend/commands/copyfrom.c
index 65b3e56cd49c6429c7806061cbcb32a39aa1ec0d..81aef4aca8a6fb729441b5bdbddd584bacf52c3e 100644 (file)
--- a/src/backend/commands/copyfrom.c
+++ b/src/backend/commands/copyfrom.c
@@ -1481,6 +1481,12 @@ BeginCopyFrom(ParseState *pstate,
                cstate->need_transcoding = true;
                cstate->conversion_proc = FindDefaultConversionProc(cstate->file_encoding,
                                                                                                                        GetDatabaseEncoding());
+               if (!OidIsValid(cstate->conversion_proc))
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_UNDEFINED_FUNCTION),
+                                        errmsg("default conversion function for encoding \"%s\" to \"%s\" does not exist",
+                                                       pg_encoding_to_char(cstate->file_encoding),
+                                                       pg_encoding_to_char(GetDatabaseEncoding()))));
        }
 
        cstate->copy_src = COPY_FILE;   /* default */