PHP currently treats namespaced names like Foo\Bar as a sequence of identifiers and namespace separator tokens. This RFC proposes to treat namespaced names as a single token, and as such allow reserved keywords to appear inside them.
There are two motivations: The first is to reduce the backwards compatibility impact of new reserved keyword additions in future versions of PHP. To give a specific example, PHP 7.4 added the fn keyword as part of arrow function support. This broke my iter library, because it was using fn as part of a namespace name. However, this breakage was entirely unnecessary! Here is a typical usage example:
// In the library: namespace iter\fn; function operator($operator, $operand = null) { ... } // In the using code: use iter\fn; iter\map(fn\operator('*', 2), $nums);
As you can see, both references of fn are part of a namespaced name: iter\fn and fn\operator. Under this proposal, these are considered perfectly legal names, and the backwards compatibility break would not have occurred.
Additionally, treating namespaced names as a single token avoids certain syntactical ambiguities. For example, the shorter attribute syntax has the following ambiguity:
function test(@@A \ B $param) {} // Can be interpreted as: function test( @@A\B $param ) {} // Or: function test( @@A \B $param ) {}
This RFC resolves this by making the first variant a syntax error, and requiring you to write whichever interpretation was intended. This proposal is a prerequisite for the implementation of the “shorter attribute syntax” in PHP 8.
PHP distinguishes four kinds of namespaced names:
Foo, which coincide with identifiers.Foo\Bar.\Foo.namespace\Foo.Each of these kinds will be represented by a distinct token:
Foo; // Before: T_STRING // After: T_STRING // Rule: {LABEL} Foo\Bar; // Before: T_STRING T_NS_SEPARATOR T_STRING // After: T_NAME_QUALIFIED // Rule: {LABEL}("\\"{LABEL})+ \Foo; // Before: T_NS_SEPARATOR T_STRING // After: T_NAME_FULLY_QUALIFIED // Rule: ("\\"{LABEL})+ namespace\Foo; // Before: T_NAMESPACE T_NS_SEPARATOR T_STRING // After: T_NAME_RELATIVE // Rule: "namespace"("\\"{LABEL})+
Individual namespace segments may contain reserved keywords:
// This is interpreted as T_LIST (i.e., as a reserved keyword): List // All of the following are interpreted as legal namespaced names: \List FooBar\List namespace\List
Whitespace is not permitted between namespace separators. If it occurs, the namespace separator will be parsed as T_NS_SEPARATOR, which will subsequently lead to a parse error. It is not possible to allow whitespace, because namespaced names commonly occur next to keywords:
class Foo implements \Bar {}
If we permitted whitespace, implements \Bar would end up being interpreted as a namespaced name. It should be noted that while this change has the potential to break some code, it also prevents programming mistakes I have seen in the wild:
// This would have previously been interpreted as a namespace-relative name, // which is an obscure PHP feature that few people know about. Now it will // result in a parse error. namespace \Foo; // This would have previously been interpreted as $foo = Foo\call($bar), // now it will result in a parse error. $foo = Foo // <- Missing semicolon \call($bar);
In the interest of consistency, the namespace declaration will accept any name, including isolated reserved keywords:
namespace iter\fn; // Legal namespace fn; // Legal
This is to avoid a discrepancy where defining symbols like iter\fn\operator is allowed, but fn\operator is not. The only restriction is that the namespace name cannot start with a namespace segment:
namespace namespace; // Illegal namespace namespace\x; // Illegal
This avoids introducing an ambiguity with namespace-relative names.
Existing code using whitespace (or comments) between namespace separators of namespaced names will now produce a parse error. An analysis of the top 2000 composer packages has found five occurrences of this issue:
sylius/sylius/src/Sylius/Bundle/ApiBundle/ApiPlatform/Metadata/Property/Factory/ExtractorPropertyMetadataFactory.php:109
\ RuntimeException
api-platform/core/src/Metadata/Extractor/AbstractExtractor.php:121
\ RuntimeException
mck89/peast/lib/Peast/Syntax/Node/JSX/JSXFragment.php:13
Peast \Syntax\Node\Expression
mck89/peast/lib/Peast/Syntax/Node/JSX/JSXOpeningElement.php:13
Peast \Syntax\Node\Expression
mck89/peast/lib/Peast/Syntax/Node/JSX/JSXElement.php:13
Peast \Syntax\Node\Expression
As such, the practical impact is very limited, and any issues are trivial to fix. On the other hand, this change will reduce the backwards-compatibility impact from any future keyword additions.
Additionally tooling based on token_get_all() will need to be adjusted to handle the new T_NAME_* tokens. In practice, this will be the main negative impact of this proposal.
Voting started 2020-07-17 and ends 2020-07-31. A 2/3 majority is required.
An earlier version of this RFC also relaxed various reserved keyword restrictions for class, function and constant declarations. Because these have to deal with more perceived ambiguities, I have dropped them from this proposal. Reserved keyword restrictions can always be lifted later on, while the change in this RFC contains a backwards-compatibility break that is best done in PHP 8.0.