Early mysql queries generate notices when query logging is enabled

Problem/Motivation

With the $conf['dev_query'] = 1;specified in settings.php, the following errors are generated at the top of the page, logged in as admin user (non-user 1).

Notice: Trying to get property of non-object in includes/database.mysqli.inc on line 108
Notice: Trying to get property of non-object in includes/database.mysqli.inc on line 108
Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at includes/database.mysqli.inc:108) in includes/bootstrap.inc on line 1172
Warning: Cannot modify header information - headers already sent by (output started at includes/database.mysqli.inc:108) in includes/bootstrap.inc on line 736
Warning: Cannot modify header information - headers already sent by (output started at includes/database.mysqli.inc:108) in includes/bootstrap.inc on line 737
Warning: Cannot modify header information - headers already sent by (output started at includes/database.mysqli.inc:108) in includes/bootstrap.inc on line 738
Warning: Cannot modify header information - headers already sent by (output started at includes/database.mysqli.inc:108) in includes/bootstrap.inc on line 739

The initial "trying to get property of non-object" error message appears twice because there are two queries that are executed before the session is created and the $user object is initialized. The reason is that drupal_is_denied() is invoked before $user is populated, which happens on the next bootstrap phase. ie. DRUPAL_BOOTSTRAP_ACCESS is executed before DRUPAL_BOOTSTRAP_SESSION.

I placed the following code snippet at the top of the _db_query() function:

  if (!is_object($user)) {
    print '<div>'. $query . '</div>';
  }

It found that the following two queries are run before the $user global is initialized as an object:

SELECT 1 FROM access WHERE type = 'host' AND LOWER('127.0.0.1') LIKE LOWER(mask) AND status = 0 LIMIT 0, 1
SELECT u.*, s.* FROM users u INNER JOIN sessions s ON u.uid = s.uid WHERE s.sid = '12345678901234567890'

This problem only affects MySQL. PGSQL is not affected because database.pgsql.inc does not contain this query comment functionality as database.mysql.inc and database.mysqli.inc do

Proposed resolution

Wrap the $user->uid part of the if statement in a !empty().

Failing the !empty($user->uid) would imply that either the $user is not an object, or that the $user->uid is false or zero (in the case of anonymous) which is precisely what this code is testing for to use the $user->name inside the query comment functionality inside the _db_query() functions.

The attached patch fixes this for both mysql drivers. The pgsql driver is not affected.

Remaining tasks

• Write patch.
• Determine if D7 or D8 are affected.
• Review patch.
• Commit.

User interface changes

Some early database query calls (that may be displayed by devel module in onscreen logs) will show as 'Anonymous' instead of the current user's name in the query's comment.

API changes

None.

Data model changes

None.