Why are PHP and Stash variables not set as expected within EE conditionals?

Question

I boiled my problem down to this template code on a template with "Allow PHP" set to "YES" and "PHP Parsing Stage" set to "Output":

{if 1 == 1}
  First block
  <?php echo '1 == 1 is true'; ?>
  <?php $test = 'hello'; ?>
{if:else}
  Second block
  <?php echo '1 == 1 is false'; ?>
  <?php $test = 'goodbye'; ?>
{/if}
<?php echo $test; ?>

The output is:

First block
1 == 1 is true
goodbye

But I would expect the output to be:

First block
1 == 1 is true
hello

I don't understand how the 1 == 1 is true line could get echoed while the variable $test gets set to "goodbye". It seems like my PHP variable assignments statements all get executed whether or not the conditional block they are in should get executed or not.

Update

This is apparently still a problem even when I eliminate the PHP from the template:

{if 1 == 1}
  1 == 1 is true
  {exp:stash:set name="test"}hello{/exp:stash:set}
{if:else}
  1 == 1 is false
  {exp:stash:set name="test"}goodbye{/exp:stash:set}
{/if}
{exp:stash:test}

The output is:

1 == 1 is true
goodbye

Answer 1

That's Parse Order. Advanced conditionals, like the one in your example, are parsed after PHP is parsed. In fact, it doesn't even matter if PHP is set on Output or Input. So, think of this step by step. First, your PHP is executed, echoing both 1 == 1 is true and 1 == 1 is false. And the var $test is first set to hello, then to goodbye, after which the latter is echoed out.

Then the advanced conditional is parsed, hiding the first block. But the setting and echoing of $test has already been done, hence goodbye remains as is.

'Tis the nature of EE's Parse Order Beast.

Answer 2

Following on from @Low's answer and your comment, it doesn't mean that you can't still use PHP successfully in templates. You just need to be mindful of the parse order when mixing PHP with EE tags.

For instance in your example if you used PHP for the full if statement then it would work as it would all be parsed at the same time from top to bottom.

Alternatively use something like Stash to set variables and then call them later in your template in among regular EE tags. You'll then be on par with the parse order again.

You can see a couple of examples of mixing PHP with EE tags on both input and output here.

As a good rule of thumb though try to keep PHP use in your templates down as much as possible for security...and sanity in regards to parse order. ;)

Answer 3

You can easily resolve parse issues like these with Switchee or Ifelse. These addons will completely remove any non-matching conditions before they are parsed. Here's how you'd fix the code sample from your post:

{exp:ifelse parse="inward"}
    {if 1 == 1}
        1 == 1 is true
        {exp:stash:set name="test"}hello{/exp:stash:set}
    {if:else}
        1 == 1 is false
        {exp:stash:set name="test"}goodbye{/exp:stash:set}
    {/if}
    {exp:stash:test}
{/exp:ifelse}

This template will output 1 == 1 is true hello as expected.

The parse="inward" parameter is key - it tells EE to parse the outer tag (the IfElse plugin) before processing the inner ones (the stash:set calls). See the EE docs for further info.