Don't allow use Foo where Foo is already a class

Classes need to take up space in the alias map (according to zend).

Suprisingly, functions and constants don't. When importing a duplicate, zend doesn't do anything and just continues, and we currently overwrite the symbol. Should I match zend on this, or is the fact that we both continue working good enough?

hphp/compiler/parser/parser.cpp

@@ -965,6 +965,7 @@ void Parser::onClass(Token &out, int type, Token &name, Token &base,
   }
   m_clsName.clear();
   m_inTrait = false;
+  registerAlias(name.text());
 }
 
 void Parser::onInterface(Token &out, Token &name, Token &base, Token &stmt,
@@ -1687,11 +1688,6 @@ void Parser::onNamespaceEnd() {
 }
 
 void Parser::onUse(const std::string &ns, const std::string &as) {
-  if (m_aliases.find(as) != m_aliases.end()) {
-    error("Cannot use %s as %s because the name is already in use: %s",
-          ns.c_str(), as.c_str(), getMessage().c_str());
-    return;
-  }
   string key = as;
   if (key.empty()) {
     size_t pos = ns.rfind(NAMESPACE_SEP);
@@ -1701,6 +1697,11 @@ void Parser::onUse(const std::string &ns, const std::string &as) {
       key = ns.substr(pos + 1);
     }
   }
+  if (m_aliases.find(key) != m_aliases.end() && m_aliases[key] != ns) {
+    error("Cannot use %s as %s because the name is already in use: %s",
+          ns.c_str(), key.c_str(), getMessage().c_str());
+    return;
+  }
   m_aliases[key] = ns;
 }
 
@@ -1787,5 +1788,13 @@ bool Parser::hasType(Token &type) {
   return false;
 }
 
+void Parser::registerAlias(std::string name) {
+  size_t pos = name.rfind(NAMESPACE_SEP);
+  if (pos != string::npos) {
+    string key = name.substr(pos + 1);
+    m_aliases[key] = name;
+  }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 }}

hphp/compiler/parser/parser.h

@@ -344,6 +344,7 @@ private:
   bool m_nsFileScope;
   std::string m_namespace; // current namespace
   hphp_string_imap<std::string> m_aliases;
+  void registerAlias(std::string name);
 };
 
 ///////////////////////////////////////////////////////////////////////////////

hphp/test/quick/ns_existing_names.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace A;
+const CO = "a";
+function f() { return "a"; }
+
+namespace B;
+const CO = "b";
+function f() { return "b"; }
+
+use A\f;
+use A\CO;
+var_dump(f());
+var_dump(CO);

hphp/test/quick/ns_existing_names.php.expect

@@ -0,0 +1,2 @@
+string(1) "b"
+string(1) "b"

hphp/test/quick/ns_existing_names_class.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace A;
+class Cl { public function __construct() { return "a"; } }
+
+namespace B;
+class Cl { public function __construct() { return "b"; } }
+use A\Cl;

hphp/test/quick/ns_existing_names_class.php.expectf

@@ -0,0 +1 @@
+HipHop Fatal error: Cannot use A\\Cl as Cl because the name is already in use: (Line: 8, Char: 9) in %s on line 8