Fix type inference for ZendParamMode

Parameters of ZendParamMode functions aren't converted to the
destination type, so don't try to apply a type.

hphp/compiler/analysis/function_scope.cpp

@@ -279,6 +279,10 @@ void FunctionScope::setParamSpecs(AnalysisResultPtr ar) {
   }
 }
 
+bool FunctionScope::isZendParamMode() const {
+  return m_attributeClassInfo & ClassInfo::ZendParamMode;
+}
+
 bool FunctionScope::isPublic() const {
   return m_modifiers && m_modifiers->isPublic();
 }
@@ -652,7 +656,8 @@ int FunctionScope::inferParamTypes(AnalysisResultPtr ar, ConstructPtr exp,
     /**
      * Duplicate the logic of getParamType(i), w/o the mutation
      */
-    TypePtr paramType(i < m_maxParam ? m_paramTypes[i] : TypePtr());
+    TypePtr paramType(i < m_maxParam && !isZendParamMode() ?
+                      m_paramTypes[i] : TypePtr());
     if (!paramType) paramType = Type::Some;
     if (valid && !canSetParamType && i < m_maxParam &&
         (!Option::HardTypeHints || !m_paramTypeSpecs[i])) {
@@ -664,8 +669,8 @@ int FunctionScope::inferParamTypes(AnalysisResultPtr ar, ConstructPtr exp,
        * expression since it'll just get converted anyways. Doing it this way
        * allows us to generate less temporaries along the way.
        */
-      TypePtr optParamType(
-          paramType->is(Type::KindOfVariant) ? Type::Some : paramType);
+      TypePtr optParamType(paramType->is(Type::KindOfVariant) ?
+                           Type::Some : paramType);
       expType = param->inferAndCheck(ar, optParamType, false);
     } else {
       expType = param->inferAndCheck(ar, Type::Some, false);

hphp/compiler/analysis/function_scope.h

@@ -109,6 +109,7 @@ public:
   bool hasImpl() const;
   void setDirectInvoke() { m_directInvoke = true; }
   bool hasDirectInvoke() const { return m_directInvoke; }
+  bool isZendParamMode() const;
   bool mayContainThis();
   bool isClosure() const;
   bool isGenerator() const;

hphp/system/idl/math.idl.json

@@ -788,7 +788,8 @@
             "name": "sqrt",
             "desc": "Returns the square root of arg.",
             "flags": [
-                "HasDocComment"
+                "HasDocComment",
+                "ZendParamMode"
             ],
             "return": {
                 "type": "Double",

hphp/test/slow/ext_math/sqrt.php

@@ -0,0 +1,6 @@
+<?php
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+var_dump(sqrt('foo'));
+var_dump(sqrt('16'));
+var_dump(sqrt(array()));

hphp/test/slow/ext_math/sqrt.php.expect

@@ -0,0 +1,3 @@
+NULL
+float(4)
+NULL