PHP: rfc:heredoc-scanner-loosening

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====== PHP RFC: Loosening heredoc/nowdoc scanner ======
  * Version: 0.9
  * Date: 2014-08-29
  * Author: Tjerk Meesters, datibbaw@php.net
  * Status: Obsolete
  * First Published at: http://wiki.php.net/rfc/heredoc-scanner-loosening


===== Introduction =====
Currently the rules for ending a heredoc or nowdoc are quite restrictive, requiring a newline after the closing identifier; this makes it more awkward to combine multiple quotations, such as in array declarations or with other operators. The [[http://php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc|manual entry]] for heredocs has a big pink box to explain those intricate details.

For instance, this is how you would declare an array comprising a heredoc and regular string:

<code php>
$strings = [<<<EOS
hello
EOS
, ' world'];
</code>

The comma that you would normally put on the same line as the previous element must now be put on the next line.

Currently, this restriction also causes a parse error with code such as this:

<code php>
return <<<EOS
Foo!
EOS; // <-- file ends here
</code>

===== Proposal =====
This proposal aims to lift the current newline restriction and make it less awkward to use heredocs and nowdocs within constructs, such as array declarations:

<code php>
$strings = [<<<EOS
a
EOS, <<<EOS
b
EOS];
</code>

Or with other operators (e.g. concatenation):

<code php>
class Test
{
    const A = <<<EOS
ab
EOS . <<<EOS
cd
EOS;
}
</code>

The proposal suggests two distinct ways in which this can be achieved:

==== Loosened restrictions ====
Ends a quotation when the closing identifier is followed by something that can't be part of an identifier.

==== Removed restrictions ====
Ends a quotation as soon as the closing identifier is encountered.

===== Backward Incompatible Changes =====
Depending on whether we choose to loosen the restrictions (defined above) or completely remove it, the following behaviour will be changed:

==== Loosened restrictions ====
The following test code (taken from the aptly called "torture the T_END_HEREDOC rules") will not work as expected:

<code php>
print <<<ENDOFHEREDOC
ENDOFHEREDOC    ;
    ENDOFHEREDOC;
ENDOFHEREDOC   
    ENDOFHEREDOC
$ENDOFHEREDOC;

ENDOFHEREDOC;
</code>

It emits "ENDOFHEREDOC    ;\nENDOFHEREDOC;" and then stop scanning, leading to a parse error on the next line.

This is a rather extreme example of trying to break the scanner; while not entirely impossible, it's most likely not based on anything one would encounter in the wild.

==== Removed restrictions ====
Removing the restrictions altogether will cause issues in code such as this:

<code php>
$s = <<<EOS
Foo bar
EOSBLA
EOS;
</code>

It emits "Foo bar" and then stops scanning, leading to a parse error at "BLA".

Although this may seem undesirable behaviour, it should be noted that the developer is in complete control of choosing the name for their enclosures; it's important to choose an enclosure that doesn't occur naturally inside the quotation.

===== Proposed PHP Version(s) =====
PHP 7

===== Unaffected PHP Functionality =====
It doesn't impact the rules that govern the contents inside the heredoc or nowdoc.

===== Proposed Voting Choices =====

Should the heredoc and nowdoc scanner be changed?

Voting choices will be:
  - No, leave the scanner as it is.
  - Yes, loosen the newline restriction with characters that can't be part of an identifier.
  - Yes, remove the newline restriction altogether.

This proposal requires a 2/3 majority as it affects the language. 

**Note:** Both "Yes" options count towards changing the current behaviour; if a single majority for  the last option can't be reached, the "loosened restrictions" will be applied.

===== Patches and Tests =====
The RFC author will provide the patches.
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