Enable pg_collation_actual_version() to work on the default collation.

Previously, it would simply return NULL, which was less useful.

Discussion: https://postgr.es/m/51fb77507cafd43fc1a2e733c23045873d93ae60.camel%40j-davis.com
Reviewed-by: Thomas Munro

diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index fcfc02d2aede9ba053450defa1e92a2d8ceaa9a5..23468cf79da55129230e5128918d6adb00ac8d63 100644 (file)
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -22,6 +22,7 @@
 #include "catalog/namespace.h"
 #include "catalog/objectaccess.h"
 #include "catalog/pg_collation.h"
+#include "catalog/pg_database.h"
 #include "commands/alter.h"
 #include "commands/collationcmds.h"
 #include "commands/comment.h"
@@ -425,33 +426,61 @@ AlterCollation(AlterCollationStmt *stmt)
 Datum
 pg_collation_actual_version(PG_FUNCTION_ARGS)
 {
-   Oid         collid = PG_GETARG_OID(0);
-   HeapTuple   tp;
-   char        collprovider;
-   Datum       datum;
-   bool        isnull;
-   char       *version;
+   Oid      collid = PG_GETARG_OID(0);
+   char     provider;
+   char    *locale;
+   char    *version;
+   Datum    datum;
+   bool     isnull;
+
+   if (collid == DEFAULT_COLLATION_OID)
+   {
+       /* retrieve from pg_database */
 
-   tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
-   if (!HeapTupleIsValid(tp))
-       ereport(ERROR,
-               (errcode(ERRCODE_UNDEFINED_OBJECT),
-                errmsg("collation with OID %u does not exist", collid)));
+       HeapTuple   dbtup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
+       if (!HeapTupleIsValid(dbtup))
+           ereport(ERROR,
+                   (errcode(ERRCODE_UNDEFINED_OBJECT),
+                    errmsg("database with OID %u does not exist", MyDatabaseId)));
 
-   collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
+       provider = ((Form_pg_database) GETSTRUCT(dbtup))->datlocprovider;
 
-   if (collprovider != COLLPROVIDER_DEFAULT)
-   {
-       datum = SysCacheGetAttr(COLLOID, tp, collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate, &isnull);
+       datum = SysCacheGetAttr(DATABASEOID, dbtup,
+                               provider == COLLPROVIDER_ICU ?
+                               Anum_pg_database_daticulocale : Anum_pg_database_datcollate,
+                               &isnull);
        if (isnull)
-           elog(ERROR, "unexpected null in pg_collation");
-       version = get_collation_actual_version(collprovider, TextDatumGetCString(datum));
+           elog(ERROR, "unexpected null in pg_database");
+
+       locale = TextDatumGetCString(datum);
+
+       ReleaseSysCache(dbtup);
    }
    else
-       version = NULL;
+   {
+       /* retrieve from pg_collation */
+
+       HeapTuple   colltp      = SearchSysCache1(COLLOID, ObjectIdGetDatum(collid));
+       if (!HeapTupleIsValid(colltp))
+           ereport(ERROR,
+                   (errcode(ERRCODE_UNDEFINED_OBJECT),
+                    errmsg("collation with OID %u does not exist", collid)));
+
+       provider = ((Form_pg_collation) GETSTRUCT(colltp))->collprovider;
+       Assert(provider != COLLPROVIDER_DEFAULT);
+       datum = SysCacheGetAttr(COLLOID, colltp,
+                               provider == COLLPROVIDER_ICU ?
+                               Anum_pg_collation_colliculocale : Anum_pg_collation_collcollate,
+                               &isnull);
+       if (isnull)
+           elog(ERROR, "unexpected null in pg_collation");
 
-   ReleaseSysCache(tp);
+       locale = TextDatumGetCString(datum);
+
+       ReleaseSysCache(colltp);
+   }
 
+   version = get_collation_actual_version(provider, locale);
    if (version)
        PG_RETURN_TEXT_P(cstring_to_text(version));
    else