not possible to enter + signs

This problem still exists in 4.7.4.

The problem lies within path_set_alias, which calls on urldecode on the given path and translates '+' into ' ' as it's supposed to do.
But in our case when we submit an url, we use + as a plus.. not as a space :(

One quick hack could be to replace the + sign with it's decoded equivalent right before we decode the path
inside path_set_alias.

  else if ($path && $alias) {
    // hack for urls with '+'
    $path = preg_replace("/[\+]/", '%2B', $path);
    $path = urldecode($path);

Other alternative is to submit taxonomy/term/651%2B652%2B653%2B654/0 instead of taxonomy/term/651+652+653+654/0.

Waiting for other suggestions...

Apparently, this problem exists in Drupal 5.0 RC2 ...

I'm not sure why the urldecode() is there... I assume it is so that you can copy/paste the path from a URL. But it's a very dangerous operation, as this problem shows.

rawurldecode() should be safer

It works when urldecode() is replaced to rawurldecode().
However, I think that urldecode() is unnecessary.

Surprisingly this problem still persists as of this writing.

This is still a valid issue (and it's caught me out before), but the patch no longer applies.

Rerolled for 7.x

drawk patch works for me - but it relies on #284899: Drupal url problem with clean urls - when that issue has been solved this patch can be applied.

Should this issue be postponed until then?

The patch submitted above works. If you remove line 90 from node.module, which reads:
$alias = urldecode($alias);
then, you will be able to create aliases with the + sign in them. The problem is that these aliases don't work. After they are created, they show a "Page not found" error.

I wrote a cleaner way then just removing the line, use this function instead of urldecode:

<?php
function urldecode_helper($string){
	$array = explode('+', $string);
	for ($i=0; $i < count($array); $i++) { 
		$array[$i] = urldecode($array[$i]);
	}
	$string = implode('+', $array);
	return $string;
}
?>

Why do these aliases not work? Can someone point out where they fail, after they are already created?

@postrational: I suggest looking at the issue I linked to in #10 - it's a problem with the clean url:s that needs to be fixed prior to this being fixable.

This should probably first be fixed in Drupal 7 and then be backported to Drupal 6 if possible.

I wonder how drupal.org could use + in url (eg http://drupal.org/project/installation+profiles)

It seems to work to use + in aliases in the latest D7 version. Can anyone else confirm?

I can save URL aliases with spaces in them, which work absolutely fine when used with '+' in URLs.

@Dave Reid: That wasn't the problem - the problem was that if you actually wanted the character + in your alias then it wasn't encoded into %2B correctly and even when it was there was a problem in #284899: Drupal url problem with clean urls which prevented that alias to be resolved properly.

#284899: Drupal url problem with clean urls is now solved in D/. Can you confirm that creating aliases with real + has also been resolved and now works as expected so that + are encoded into %2B and that aliases containing such %2B characters can be used and resolved properly?

Changing status until anyone confirms this issue.

Tested in D7 & D8 ... all is well with the world