The following class will cause Doxygen to hang on "Computing class inheritance relations...". Note the "Foo" namespace and the coexisting "use Foo\Foo;" statement:

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<?php

namespace Foo\Data;

use Foo\Foo;

class DataSet implements IteratorAggregate {

}
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If you either change the namespace, one of the "Foo" in the use statement or move the "use IteratorAggregate" below "Foo\Foo", it works. The problem also disappears as soon as no global import is involved.

Working examples:

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<?php

namespace Foo\Data;

use IteratorAggregate;
use Foo\AnotherFoo;

class DataSet implements IteratorAggregate {

}

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<?php

namespace AnotherFoo\Data;

use IteratorAggregate;
use AnotherFoo\Foo;

class DataSet implements IteratorAggregate {

}

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<?php

namespace Foo\Data;

use Foo\Foo;
use IteratorAggregate;

class DataSet implements IteratorAggregate {

}

-----
<?php

namespace Foo\Data;

use Foo\Foo;

class DataSet {

}
-----


Doxygen output for the first example:

Searching for include files...
Searching for example files...
Searching for images...
Searching for dot files...
Searching for msc files...
Searching for files to exclude
Searching for files to process...
Reading and parsing tag files
Reading [***]/Dataset.php...
Parsing file [***]/Dataset.php...
Building group list...
Building directory list...
Building namespace list...
Building file list...
Building class list...
Associating documentation with classes...
Computing nesting relations for classes...
Building example list...
Searching for enumerations...
Searching for documented typedefs...
Searching for members imported via using declarations...
Searching for included using directives...
Searching for documented variables...
Building member list...
Searching for friends...
Searching for documented defines...
Computing class inheritance relations...