Make the locale comparison in pg_upgrade more lenient

If the locale names are not equal, try to canonicalize both of them by
passing them to setlocale(). Before, we only canonicalized the old cluster's
locale if upgrading from a 8.4-9.2 server, but we also need to canonicalize
when upgrading from a pre-8.4 server. That was an oversight in the code. But
we should also canonicalize on newer server versions, so that we cope if the
canonical form changes from one release to another. I'm about to do just
that to fix bug #11431, by mapping a locale name that contains non-ASCII
characters to a pure-ASCII alias of the same locale.

This is partial backpatch of commit 33755e8
in master. Apply to 9.2, 9.3 and 9.4. The canonicalization code didn't exist
before 9.2. In 9.2 and 9.3, this effectively also back-patches the changes
from commit 5827472, to be more lax about
the spelling of the encoding in the locale names.

Author: hlinnaka

contrib/pg_upgrade/check.c

@@ -17,7 +17,7 @@ static void set_locale_and_encoding(ClusterInfo *cluster);
 static void check_new_cluster_is_empty(void);
 static void check_locale_and_encoding(ControlData *oldctrl,
 						  ControlData *newctrl);
-static bool equivalent_locale(const char *loca, const char *locb);
+static bool equivalent_locale(int category, const char *loca, const char *locb);
 static bool equivalent_encoding(const char *chara, const char *charb);
 static void check_is_super_user(ClusterInfo *cluster);
 static void check_for_prepared_transactions(ClusterInfo *cluster);
@@ -370,23 +370,8 @@ set_locale_and_encoding(ClusterInfo *cluster)
 		i_datcollate = PQfnumber(res, "datcollate");
 		i_datctype = PQfnumber(res, "datctype");
 
-		if (GET_MAJOR_VERSION(cluster->major_version) < 902)
-		{
-			/*
-			 * Pre-9.2 did not canonicalize the supplied locale names to match
-			 * what the system returns, while 9.2+ does, so convert pre-9.2 to
-			 * match.
-			 */
-			ctrl->lc_collate = get_canonical_locale_name(LC_COLLATE,
-								pg_strdup(PQgetvalue(res, 0, i_datcollate)));
-			ctrl->lc_ctype = get_canonical_locale_name(LC_CTYPE,
-								  pg_strdup(PQgetvalue(res, 0, i_datctype)));
-		}
-		else
-		{
-			ctrl->lc_collate = pg_strdup(PQgetvalue(res, 0, i_datcollate));
-			ctrl->lc_ctype = pg_strdup(PQgetvalue(res, 0, i_datctype));
-		}
+		ctrl->lc_collate = pg_strdup(PQgetvalue(res, 0, i_datcollate));
+		ctrl->lc_ctype = pg_strdup(PQgetvalue(res, 0, i_datctype));
 
 		PQclear(res);
 	}
@@ -418,10 +403,10 @@ static void
 check_locale_and_encoding(ControlData *oldctrl,
 						  ControlData *newctrl)
 {
-	if (!equivalent_locale(oldctrl->lc_collate, newctrl->lc_collate))
+	if (!equivalent_locale(LC_COLLATE, oldctrl->lc_collate, newctrl->lc_collate))
 		pg_fatal("lc_collate cluster values do not match:  old \"%s\", new \"%s\"\n",
 				 oldctrl->lc_collate, newctrl->lc_collate);
-	if (!equivalent_locale(oldctrl->lc_ctype, newctrl->lc_ctype))
+	if (!equivalent_locale(LC_CTYPE, oldctrl->lc_ctype, newctrl->lc_ctype))
 		pg_fatal("lc_ctype cluster values do not match:  old \"%s\", new \"%s\"\n",
 				 oldctrl->lc_ctype, newctrl->lc_ctype);
 	if (!equivalent_encoding(oldctrl->encoding, newctrl->encoding))
@@ -434,39 +419,46 @@ check_locale_and_encoding(ControlData *oldctrl,
  *
  * Best effort locale-name comparison.  Return false if we are not 100% sure
  * the locales are equivalent.
+ *
+ * Note: The encoding parts of the names are ignored. This function is
+ * currently used to compare locale names stored in pg_database, and
+ * pg_database contains a separate encoding field. That's compared directly
+ * in check_locale_and_encoding().
  */
 static bool
-equivalent_locale(const char *loca, const char *locb)
+equivalent_locale(int category, const char *loca, const char *locb)
 {
-	const char *chara = strrchr(loca, '.');
-	const char *charb = strrchr(locb, '.');
-	int			lencmp;
-
-	/* If they don't both contain an encoding part, just do strcasecmp(). */
-	if (!chara || !charb)
-		return (pg_strcasecmp(loca, locb) == 0);
+	const char *chara;
+	const char *charb;
+	char	   *canona;
+	char	   *canonb;
+	int			lena;
+	int			lenb;
 
 	/*
-	 * Compare the encoding parts.  Windows tends to use code page numbers for
-	 * the encoding part, which equivalent_encoding() won't like, so accept if
-	 * the strings are case-insensitive equal; otherwise use
-	 * equivalent_encoding() to compare.
+	 * If the names are equal, the locales are equivalent. Checking this
+	 * first avoids calling setlocale() in the common case that the names
+	 * are equal. That's a good thing, if setlocale() is buggy, for example.
 	 */
-	if (pg_strcasecmp(chara + 1, charb + 1) != 0 &&
-		!equivalent_encoding(chara + 1, charb + 1))
-		return false;
+	if (pg_strcasecmp(loca, locb) == 0)
+		return true;
 
 	/*
-	 * OK, compare the locale identifiers (e.g. en_US part of en_US.utf8).
-	 *
-	 * It's tempting to ignore non-alphanumeric chars here, but for now it's
-	 * not clear that that's necessary; just do case-insensitive comparison.
+	 * Not identical. Canonicalize both names, remove the encoding parts,
+	 * and try again.
 	 */
-	lencmp = chara - loca;
-	if (lencmp != charb - locb)
-		return false;
+	canona = get_canonical_locale_name(category, loca);
+	chara = strrchr(canona, '.');
+	lena = chara ? (chara - canona) : strlen(canona);
+
+	canonb = get_canonical_locale_name(category, locb);
+	charb = strrchr(canonb, '.');
+	lenb = charb ? (charb - canonb) : strlen(canonb);
+
+	if (lena == lenb && pg_strncasecmp(canona, canonb, lena) == 0)
+		return true;
 
-	return (pg_strncasecmp(loca, locb, lencmp) == 0);
+	return false;
 }
 
 /*