Notice undefined variable $user when posting comment without cookies set

[c3mdigital]

Just noticed this in 3.5 (21468).
Theme: Twentytweleve
No Plugins active

Notice: Undefined variable: user in /Users/chris/Sites/newpatch/wp-includes/comment.php on line 658
Call Stack
#	Time	Memory	Function	Location
1	0.0025	268152	{main}( )	../wp-comments-post.php:0
2	0.2503	15399872 wp_new_comment( )	../wp-comments-post.php:90
3	0.2522	15414424	 wp_allow_comment( )	../comment.php:1358

Which also causes multiple cannot modify headers warnings:

Warning: Cannot modify header information - headers already sent by (output started at /Users/chris/Sites/newpatch/wp-includes/comment.php:658) in /Users/chris/Sites/newpatch/wp-includes/comment.php on line 586
Call Stack
#	Time	Memory	Function	Location
1	0.0025	268152	{main}( )../wp-comments-post.php:0
2	0.3219	16238192	  do_action( )	../wp-comments-post.php:93
3	0.3219	16239784	  call_user_func_array ( )	../plugin.php:406
4	0.3219	16239816	  wp_set_comment_cookies( )	../plugin.php:406
5	0.3219	16240416	  setcookie ( )	../comment.php:586

Warning: Cannot modify header information - headers already sent by (output started at /Users/chris/Sites/newpatch/wp-includes/comment.php:658) in /Users/chris/Sites/newpatch/wp-includes/pluggable.php on line 884
Call Stack
#	Time	Memory	Function	Location
1	0.0025	268152	{main}( )	../wp-comments-post.php:0
2	0.3246	16239184	wp_safe_redirect( )	../wp-comments-post.php:98
3	0.3250	16239512	wp_redirect( )	../pluggable.php:931
4	0.3254	16251096	header ( )	../pluggable.php:884

Steps to reproduce:

1. Update to latest version
2. Clear cookies and logout or start a new private browsing session.
3. Post comment

Wrapping the $user variable with isset() fixes the problem.

[nacin]

Looks good. It's meant to be a truth check, so ! empty() is proper.

[SergeyBiryukov]

Introduced in [21413].

[ryan]

In [21506]:

Add isset() check to avoid notice. Props c3mdigital. fixes #21512