Allow NULL version for individual collations.

Remove the documented restriction that collation providers must either
return NULL for all collations or non-NULL for all collations.

Use NULL for glibc collations like "C.UTF-8", which might otherwise lead
future proposed commits to force unnecessary index rebuilds.

Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Discussion: https://postgr.es/m/CA%2BhUKGJvqup3s%2BJowVTcacZADO6dOhfdBmvOPHLS3KXUJu41Jw%40mail.gmail.com

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 64fd3ae18a8dd27ccf4be185bab449ed4c261077..b42122f9ceaf22cd966af93d4c3831d106767b34 100644 (file)
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1505,10 +1505,6 @@ pg_newlocale_from_collation(Oid collid)
 /*
  * Get provider-specific collation version string for the given collation from
  * the operating system/library.
- *
- * A particular provider must always either return a non-NULL string or return
- * NULL (if it doesn't support versions).  It must not return NULL for some
- * collcollate and not NULL for others.
  */
 char *
 get_collation_actual_version(char collprovider, const char *collcollate)
@@ -1540,6 +1536,23 @@ get_collation_actual_version(char collprovider, const char *collcollate)
    if (collprovider == COLLPROVIDER_LIBC)
    {
 #if defined(__GLIBC__)
+       char       *copy = pstrdup(collcollate);
+       char       *copy_suffix = strstr(copy, ".");
+       bool        need_version = true;
+
+       /*
+        * Check for names like C.UTF-8 by chopping off the encoding suffix on
+        * our temporary copy, so we can skip the version.
+        */
+       if (copy_suffix)
+           *copy_suffix = '\0';
+       if (pg_strcasecmp("c", copy) == 0 ||
+           pg_strcasecmp("posix", copy) == 0)
+           need_version = false;
+       pfree(copy);
+       if (!need_version)
+           return NULL;
+
        /* Use the glibc version because we don't have anything better. */
        collversion = pstrdup(gnu_get_libc_version());
 #endif