write_nondefault_variables must take care to write custom_variable_classes

first; otherwise backends reading the file might reject values of custom
variables.  Per experimentation with auto_explain.

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.485 2009/01/02 01:16:02 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.486 2009/01/02 02:02:10 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -6677,43 +6677,19 @@ is_newvalue_equal(struct config_generic * record, const char *newvalue)
 #ifdef EXEC_BACKEND
 
 /*
- *	This routine dumps out all non-default GUC options into a binary
+ *	These routines dump out all non-default GUC options into a binary
  *	file that is read by all exec'ed backends.  The format is:
  *
  *		variable name, string, null terminated
  *		variable value, string, null terminated
  *		variable source, integer
  */
-void
-write_nondefault_variables(GucContext context)
+static void
+write_one_nondefault_variable(FILE *fp, struct config_generic *gconf)
 {
-	int			i;
-	int			elevel;
-	FILE	   *fp;
-
-	Assert(context == PGC_POSTMASTER || context == PGC_SIGHUP);
-
-	elevel = (context == PGC_SIGHUP) ? LOG : ERROR;
-
-	/*
-	 * Open file
-	 */
-	fp = AllocateFile(CONFIG_EXEC_PARAMS_NEW, "w");
-	if (!fp)
-	{
-		ereport(elevel,
-				(errcode_for_file_access(),
-				 errmsg("could not write to file \"%s\": %m",
-						CONFIG_EXEC_PARAMS_NEW)));
+	if (gconf->source == PGC_S_DEFAULT)
 		return;
-	}
-
-	for (i = 0; i < num_guc_variables; i++)
-	{
-		struct config_generic *gconf = guc_variables[i];
 
-		if (gconf->source != PGC_S_DEFAULT)
-		{
 	fprintf(fp, "%s", gconf->name);
 	fputc(0, fp);
 
@@ -6723,10 +6699,10 @@ write_nondefault_variables(GucContext context)
 		{
 			struct config_bool *conf = (struct config_bool *) gconf;
 
-						if (*conf->variable == 0)
-							fprintf(fp, "false");
-						else
+			if (*conf->variable)
 				fprintf(fp, "true");
+			else
+				fprintf(fp, "false");
 		}
 		break;
 
@@ -6759,7 +6735,8 @@ write_nondefault_variables(GucContext context)
 		{
 			struct config_enum *conf = (struct config_enum *) gconf;
 						
-						fprintf(fp, "%s", config_enum_lookup_by_value(conf, *conf->variable));
+			fprintf(fp, "%s",
+					config_enum_lookup_by_value(conf, *conf->variable));
 		}
 		break;
 	}
@@ -6767,7 +6744,47 @@ write_nondefault_variables(GucContext context)
 	fputc(0, fp);
 
 	fwrite(&gconf->source, sizeof(gconf->source), 1, fp);
+}
+
+void
+write_nondefault_variables(GucContext context)
+{
+	int			elevel;
+	FILE	   *fp;
+	struct config_generic *cvc_conf;
+	int			i;
+
+	Assert(context == PGC_POSTMASTER || context == PGC_SIGHUP);
+
+	elevel = (context == PGC_SIGHUP) ? LOG : ERROR;
+
+	/*
+	 * Open file
+	 */
+	fp = AllocateFile(CONFIG_EXEC_PARAMS_NEW, "w");
+	if (!fp)
+	{
+		ereport(elevel,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m",
+						CONFIG_EXEC_PARAMS_NEW)));
+		return;
 	}
+
+	/*
+	 * custom_variable_classes must be written out first; otherwise we might
+	 * reject custom variable values while reading the file.
+	 */
+	cvc_conf = find_option("custom_variable_classes", false, ERROR);
+	if (cvc_conf)
+		write_one_nondefault_variable(fp, cvc_conf);
+
+	for (i = 0; i < num_guc_variables; i++)
+	{
+		struct config_generic *gconf = guc_variables[i];
+
+		if (gconf != cvc_conf)
+			write_one_nondefault_variable(fp, gconf);
 	}
 
 	if (FreeFile(fp))