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5 months ago

Note some undocumented details about exceptions thrown from 'finally' blocks. 

When exception is thrown from 'finally' block, it overrides the original not-caught (or re-thrown) exception. So the behavior is similar to 'return': value returned from 'finally' overrides the one returned earlier. And the original exception is automatically appended to the exceptions chain, i.e. becomes 'previous' for the new one. Example:
<?php
try {
    try {
        throw new Exception('thrown from try');
    } finally {
        throw new Exception('thrown from finally');
    }
} catch(Exception $e) {
    echo $e->getMessage();
    echo PHP_EOL;
    echo $e->getPrevious()->getMessage();
} 

// will output:
// thrown from finally
// thrown from try
?>

Example with re-throwing:
<?php
try {
    try {
        throw new Exception('thrown from try');
    } catch (Exception $e) {
        throw new Exception('thrown from catch');
    } finally {
        throw new Exception('thrown from finally');
    }
} catch(Exception $e) {
    echo $e->getMessage();
    echo PHP_EOL;
    echo $e->getPrevious()->getMessage();
} 

// will output:
// thrown from finally
// thrown from catch
?>

The same happens even if explicitly pass null as previous exception:
<?php
try {
    try {
        throw new Exception('thrown from try');
    } finally {
        throw new Exception('thrown from finally', null, null);
    }
} catch(Exception $e) {
    echo $e->getMessage();
    echo PHP_EOL;
    echo $e->getPrevious()->getMessage();
} 

// will output:
// thrown from finally
// thrown from try
?>

Also it is possible to pass previous exception explicitly, the 'original' one will be still appended to the chain, e.g.:
<?php
try {
    try {
        throw new Exception('thrown from try');
    } finally {
        throw new Exception(
            'thrown from finally',
            null, 
            new Exception('Explicitly set previous!')
        );
    }
} catch(Exception $e) {
    echo $e->getMessage();
    echo PHP_EOL;
    echo $e->getPrevious()->getMessage();
    echo PHP_EOL;
    echo $e->getPrevious()->getPrevious()->getMessage();
} 

// will output:
// thrown from finally
// Explicitly set previous!
// thrown from try
?>

This seems to be true for versions 5.6-8.2.
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