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Doc Bug #74257 "namespace \X" does not work to declare a namespace
Submitted: 2017-03-16 12:47 UTC Modified: 2019-01-31 01:30 UTC
From: david at grudl dot com Assigned:
Status: Open Package: Scripting Engine problem
PHP Version: 7.1.2 OS:
Private report: No CVE-ID: None
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 [2017-03-16 12:47 UTC] david at grudl dot com
Leading slash in namespace declaration can cause silent ignorance of namespace declaration.

Test script:

define('X', 'Y');

namespace \X;

class Test

echo Test::class;

Expected result:
Fatal error: Namespace declaration statement has to be the very first statement or after any declare call in the script

Actual result:


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 [2017-03-16 16:46 UTC]
This is not a bug, but rather a feature in namespaces known as relative names.

In short, the following line:
namespace \X;

is not a namespace *declaration*, but rather an *expression* that resolves to the symbol X of the current namespace. The "namespace \" part (where space is optional) is either evaluated to the currently defined namespace (it is simply ignored for the global namespace).

When utilising this feature, symbols that are not found in the current namespace will not fallback to the globally defined functions or constants.

So, the following works:

But the following will error (due to an undefined PHP_ZTS constant in the current namespace):
namespace test;

Whilst obviously the following will work as expected (by falling back to the globally defined PHP_ZTS constant):
namespace test;

See the manual for further information:
 [2017-03-16 16:46 UTC]
-Status: Open +Status: Not a bug
 [2017-03-16 16:46 UTC]
^ See above comment...
 [2019-01-31 01:16 UTC] roy-orbison at devo dot net dot au
This is definitely a bug. If PHP devs really think it's a feature, why isn't it documented in "Defining Namespaces"? There is no way anyone would expect the following to be anything other than a definition.

namespace \Foo\Bar;

Accessing members of a namespace relative to global is done with a leading backslash, so why not the same for defining? It should at least be a syntax error rather than evaluate and cause a fatal error or silently fail. That type of expression could only read a constant without doing any assignment, thus have no effect on other userspace state, right? So what's the point of allowing it without even a warning?
 [2019-01-31 01:30 UTC]
-Summary: Leading slash in namespace declaration +Summary: "namespace \X" does not work to declare a namespace -Status: Not a bug +Status: Open -Type: Bug +Type: Documentation Problem -Package: Compile Failure +Package: Scripting Engine problem
 [2019-01-31 01:30 UTC]
Keep in mind OP had to define X as a constant. In the real world namespaces have more meaningful names and it's unlikely there will be a constant by the same name, so code would create an error.

Additionally, "namespace\" is documented in "namespace keyword and __NAMESPACE__ constant"
 [2019-01-31 22:51 UTC] roy-orbison at devo dot net dot au
Indeed, but that error is not picked up by linting, and the message is for an undefined constant.
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