Explicitly check if a file has already been required before requiring it

[jeskew]

This would address #3003 by assigning an identifier to each included file during AutoloadGenerator::dump. Currently, this identifier is the value returned by md5_file (to address the concern raised in guzzle/guzzle#676 (comment)), but it could also be a logical file address such as $packageName::$relativePath, e.g. guzzlehttp/guzzle::src/functions.php.

This is preferable to simple changing require to require_once because it prevents two copies of the same file from being loaded, as would happen if a globally installed package loads project's autoloader and both rely on the same package. A known example of this is using a globally installed copy of CodeCeption on a project requiring Guzzle.

Would also address:
guzzle/guzzle#1146
guzzle/psr7#22

[alcohol]

Wouldn't it be easier instead if perhaps the Composer autoloader defined a constant (e.g. COMPOSER_AUTOLOADER_LOADED), and people could use that to check if the autoloader has been loaded already or not?

Basically approaching the situation from a different angle. Just trying to add more ideas. :-)

[jeskew]

@alcohol The two autoloaders might load different files (e.g., if you install PHPUnit globally and Guzzle locally), so I'm not sure a simple flag would be useful.

[alcohol]

What if the value of it was the resolved path to the autoloader? For
comparison values.
On Jun 28, 2015 10:45 PM, "Jonathan Eskew" notifications@github.com wrote:

@alcohol https://github.com/alcohol The two autoloaders might load
different files (e.g., if you install PHPUnit globally and Guzzle locally),
so I'm not sure a simple flag would be useful.

—
Reply to this email directly or view it on GitHub
#4186 (comment).

[jeskew]

I don't believe that would solve the issue reported in #3003, which was that the same file, existing in two locations on disk, could be included by two separate autoloaders.

[alcohol]

as would happen if a package is installed globally and in a project

I don't understand how this is relevant? Globally installed doesn't mean it is always loaded. You would still have to explicitly include ~/.composer/vendor/autoloader.php first if I am not mistaken?

[jeskew]

That's correct, and that is the issue that was reported. #3003 (comment)

[stof]

@alcohol the problem occurs when a tool installed globally (PHPUnit for instance) also loads the autoloading of your project after loading the global one

[jeskew]

@stof Do you think this is a good way to solve the problem? I used file checksums instead of logical identifiers so that accidentally loading two versions of the same package would continue to cause a failure, but using something like $packageName::$pathRelativeToVendorDir => $absolutePath would also be viable.

[Seldaek]

Thanks!