Treat namespaced names as single token

Namespace names are now lexed as single tokens of type
T_NAME_QUALIFIED, T_NAME_FULLY_QUALIFIED or T_NAME_RELATIVE.

RFC: https://wiki.php.net/rfc/namespaced_names_as_token

Closes GH-5827.

Author: nikic

UPGRADING

@@ -204,6 +204,10 @@ PHP 8.0 UPGRADE NOTES
     numbers and numeric strings continue to work as before. Notably, this means
     that `0 == "not-a-number"` is considered false now.
     RFC: https://wiki.php.net/rfc/string_to_number_comparison
+  . Namespaced names can no longer contain whitespace: While `Foo\Bar` will be
+    recognized as a namespaced name, `Foo \ Bar` will not. Conversely, reserved
+    keywords are now permitted as namespace segments.
+    RFC: https://wiki.php.net/rfc/namespaced_names_as_token
 
 - COM:
   . Removed the ability to import case-insensitive constants from type
@@ -509,6 +513,11 @@ PHP 8.0 UPGRADE NOTES
     instead be part of a following T_WHITESPACE token. It should be noted that
     T_COMMENT is not always followed by whitespace, it may also be followed by
     T_CLOSE_TAG or end-of-file.
+  . Namespaced names are now represented using the T_NAME_QUALIFIED (Foo\Bar),
+    T_NAME_FULLY_QUALIFIED (\Foo\Bar) and T_NAME_RELATIVE (namespace\Foo\Bar)
+    tokens. T_NS_SEPARATOR is only used for standalone namespace separators,
+    and only syntactially valid in conjunction with group use declarations.
+    RFC: https://wiki.php.net/rfc/namespaced_names_as_token
 
 - XML:
   . xml_parser_create(_ns) will now return an XmlParser object rather than a

Zend/tests/attributes/019_variable_attribute_name.phpt

@@ -8,4 +8,4 @@ class A {}
 
 ?>
 --EXPECTF--
-Parse error: syntax error, unexpected variable "$x", expecting identifier or "static" or "namespace" or "\" in %s on line %d
+Parse error: syntax error, unexpected variable "$x" in %s on line %d

Zend/tests/bug43343.phpt

@@ -8,4 +8,4 @@ $foo = 'bar';
 var_dump(new namespace::$foo);
 ?>
 --EXPECTF--
-Parse error: %s error%sexpecting%s"\"%sin %sbug43343.php on line 5
+Parse error: syntax error, unexpected token "namespace" in %s on line %d

Zend/tests/bug55086.phpt

@@ -26,7 +26,7 @@ namespace N2 {
     echo $a->hello(), PHP_EOL;
     echo $a->foo(), PHP_EOL;
     try {
-    } catch(namespace \Foo $e)
+    } catch (namespace\Foo $e)
     {
     }
 }

Zend/tests/grammar/regression_010.phpt

@@ -5,8 +5,11 @@ Test to check regressions on T_IMPLEMENTS followed by a T_NS_SEPARATOR
 
 interface A{}
 
+// No longer considered legal in PHP 8.
 class B implements\A {}
 
 echo "Done", PHP_EOL;
---EXPECT--
-Done
+
+?>
+--EXPECTF--
+Parse error: syntax error, unexpected namespaced name "implements\A", expecting "{" in %s on line %d

Zend/tests/namespace_name_namespace.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Cannot use "namespace" as namespace name, due to conflict with ns-relative names
+--FILE--
+<?php
+
+namespace NAMEspace;
+
+?>
+--EXPECTF--
+Fatal error: Cannot use 'NAMEspace' as namespace name in %s on line %d

Zend/tests/namespace_name_namespace_start.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Cannot use "namespace\xyz" as namespace name, due to conflict with ns-relative names
+--FILE--
+<?php
+
+namespace NAMEspace\xyz;
+
+?>
+--EXPECTF--
+Parse error: syntax error, unexpected namespace-relative name "NAMEspace\xyz", expecting "{" in %s on line %d

Zend/tests/namespace_name_reserved_keywords.phpt

@@ -0,0 +1,37 @@
+--TEST--
+Reserved keywords in namespace name
+--FILE--
+<?php
+
+namespace iter\fn {
+    function test() {
+        echo __FUNCTION__, "\n";
+    }
+}
+
+namespace fn {
+    function test() {
+        echo __FUNCTION__, "\n";
+    }
+}
+
+namespace self {
+    function test() {
+        echo __FUNCTION__, "\n";
+    }
+}
+
+namespace {
+    use iter\fn;
+    use function fn\test as test2;
+    use function self\test as test3;
+    fn\test();
+    test2();
+    test3();
+}
+
+?>
+--EXPECT--
+iter\fn\test
+fn\test
+self\test

Zend/tests/namespaced_name_whitespace.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Whitespace between namespace separators is no longer allowed
+--FILE--
+<?php
+
+Foo \ Bar \ Baz;
+
+?>
+--EXPECTF--
+Parse error: syntax error, unexpected token "\" in %s on line %d

Zend/tests/ns_096.phpt

@@ -7,4 +7,4 @@ use Foo\Bar\{\Baz};
 
 ?>
 --EXPECTF--
-Parse error: syntax error, unexpected token "\", expecting identifier or "function" or "const" in %s on line %d
+Parse error: syntax error, unexpected fully qualified name "\Baz", expecting identifier or namespaced name or "function" or "const" in %s on line %d