$is_nginx global not defined in vars.php

[johnjamesjacoby]

vars.php defines environmental globals used throughout WordPress. When $is_nginx was added in r25456, it was not added to the global definitions at the top of vars.php.

See #18852, #25098.

[johnjamesjacoby]

Because vars.php is included in the global scope and the only place that references the $is_nginx global directly (options-permalink.php) is also included in the global scope, this does not cause any problems. got_url_rewrite uses $GLOBALS['is_nginx'] rather than define the global, which is how it gets around it also.

Arguably, we could delete the definitions completely at the top of the file, since vars.php is only included directly via wp-settings.php in the global scope, meaning all variables in vars.php are considered global anyways.

Striving for consistency, would be nice to see it added. Additionally, the doc-block at the top of vars.php should be updated to include the nginx check.

[nacin]

The definitions exist for when WordPress isn't loaded in global scope, like during unit tests.

[nacin]

In 25996:

Explicitly globalize $is_nginx in vars.php.

props johnjamesjacoby.
fixes #25776.