Index: clang-tools-extra/trunk/clang-tidy/cert/CERTTidyModule.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/cert/CERTTidyModule.cpp
+++ clang-tools-extra/trunk/clang-tidy/cert/CERTTidyModule.cpp
@@ -17,6 +17,7 @@
 #include "../misc/StaticAssertCheck.h"
 #include "../misc/ThrowByValueCatchByReferenceCheck.h"
 #include "CommandProcessorCheck.h"
+#include "DontModifyStdNamespaceCheck.h"
 #include "FloatLoopCounter.h"
 #include "LimitedRandomnessCheck.h"
 #include "SetLongJmpCheck.h"
@@ -37,6 +38,8 @@
     CheckFactories.registerCheck<VariadicFunctionDefCheck>("cert-dcl50-cpp");
     CheckFactories.registerCheck<misc::NewDeleteOverloadsCheck>(
         "cert-dcl54-cpp");
+    CheckFactories.registerCheck<DontModifyStdNamespaceCheck>(
+        "cert-dcl58-cpp");
     CheckFactories.registerCheck<google::build::UnnamedNamespaceInHeaderCheck>(
         "cert-dcl59-cpp");
     // OOP
Index: clang-tools-extra/trunk/clang-tidy/cert/CMakeLists.txt
===================================================================
--- clang-tools-extra/trunk/clang-tidy/cert/CMakeLists.txt
+++ clang-tools-extra/trunk/clang-tidy/cert/CMakeLists.txt
@@ -3,6 +3,7 @@
 add_clang_library(clangTidyCERTModule
   CERTTidyModule.cpp
   CommandProcessorCheck.cpp
+  DontModifyStdNamespaceCheck.cpp
   FloatLoopCounter.cpp
   LimitedRandomnessCheck.cpp
   SetLongJmpCheck.cpp
Index: clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.h
===================================================================
--- clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.h
+++ clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.h
@@ -0,0 +1,36 @@
+//===--- DontModifyStdNamespaceCheck.h - clang-tidy--------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CERT_DONT_MODIFY_STD_NAMESPACE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CERT_DONT_MODIFY_STD_NAMESPACE_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace cert {
+
+/// Modification of the std or posix namespace can result in undefined behavior.
+/// This check warns for such modifications.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/cert-msc53-cpp.html
+class DontModifyStdNamespaceCheck : public ClangTidyCheck {
+public:
+  DontModifyStdNamespaceCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace cert
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CERT_DONT_MODIFY_STD_NAMESPACE_H
Index: clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.cpp
+++ clang-tools-extra/trunk/clang-tidy/cert/DontModifyStdNamespaceCheck.cpp
@@ -0,0 +1,49 @@
+//===--- DontModifyStdNamespaceCheck.cpp - clang-tidy----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DontModifyStdNamespaceCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace cert {
+
+void DontModifyStdNamespaceCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(
+      namespaceDecl(unless(isExpansionInSystemHeader()),
+                    anyOf(hasName("std"), hasName("posix")),
+                    has(decl(unless(anyOf(
+                        functionDecl(isExplicitTemplateSpecialization()),
+                        cxxRecordDecl(isExplicitTemplateSpecialization()))))))
+          .bind("nmspc"),
+      this);
+}
+
+void DontModifyStdNamespaceCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *N = Result.Nodes.getNodeAs<NamespaceDecl>("nmspc");
+
+  // Only consider top level namespaces.
+  if (N->getParent() != Result.Context->getTranslationUnitDecl())
+    return;
+
+  diag(N->getLocation(),
+       "modification of %0 namespace can result in undefined behavior")
+      << N;
+}
+
+} // namespace cert
+} // namespace tidy
+} // namespace clang
Index: clang-tools-extra/trunk/docs/ReleaseNotes.rst
===================================================================
--- clang-tools-extra/trunk/docs/ReleaseNotes.rst
+++ clang-tools-extra/trunk/docs/ReleaseNotes.rst
@@ -57,6 +57,11 @@
 Improvements to clang-tidy
 --------------------------
 
+- New `cert-dcl58-cpp
+  <http://clang.llvm.org/extra/clang-tidy/checks/cert-dcl58-cpp.html>`_ check
+
+  Finds modification of the ``std`` or ``posix`` namespace.
+
 - New `readability-misleading-indentation
   <http://clang.llvm.org/extra/clang-tidy/checks/readability-misleading-indentation.html>`_ check
 
Index: clang-tools-extra/trunk/docs/clang-tidy/checks/cert-dcl58-cpp.rst
===================================================================
--- clang-tools-extra/trunk/docs/clang-tidy/checks/cert-dcl58-cpp.rst
+++ clang-tools-extra/trunk/docs/clang-tidy/checks/cert-dcl58-cpp.rst
@@ -0,0 +1,21 @@
+.. title:: clang-tidy - cert-dcl58-cpp
+
+cert-dcl58-cpp
+==============
+
+Modification of the ``std`` or ``posix`` namespace can result in undefined
+behavior.
+This check warns for such modifications.
+
+Examples:
+
+.. code-block:: c++
+
+  namespace std {
+    int x; // May cause undefined behavior.
+  }
+
+
+This check corresponds to the CERT C++ Coding Standard rule
+`DCL58-CPP. Do not modify the standard namespaces
+<https://www.securecoding.cert.org/confluence/display/cplusplus/DCL58-CPP.+Do+not+modify+the+standard+namespaces>`_.
Index: clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst
===================================================================
--- clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst
+++ clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst
@@ -8,6 +8,7 @@
    cert-dcl03-c (redirects to misc-static-assert) <cert-dcl03-c>
    cert-dcl50-cpp
    cert-dcl54-cpp (redirects to misc-new-delete-overloads) <cert-dcl54-cpp>
+   cert-dcl58-cpp
    cert-dcl59-cpp (redirects to google-build-namespaces) <cert-dcl59-cpp>
    cert-env33-c
    cert-err09-cpp (redirects to misc-throw-by-value-catch-by-reference) <cert-err09-cpp>
Index: clang-tools-extra/trunk/test/clang-tidy/Inputs/Headers/system-header-simulation.h
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/Inputs/Headers/system-header-simulation.h
+++ clang-tools-extra/trunk/test/clang-tidy/Inputs/Headers/system-header-simulation.h
@@ -0,0 +1,24 @@
+#pragma clang system_header
+
+namespace std {
+
+template<class T, T v>
+struct integral_constant {
+    static constexpr T value = v;
+    typedef T value_type;
+    typedef integral_constant type;
+    constexpr operator value_type() const noexcept { return value; }
+};
+
+template <bool B>
+using bool_constant = integral_constant<bool, B>;
+using true_type = bool_constant<true>;
+using false_type = bool_constant<false>;
+
+template<class T>
+struct is_error_code_enum : false_type {};
+
+template<class T>
+void swap(T &a, T &b);
+}
+
Index: clang-tools-extra/trunk/test/clang-tidy/cert-dcl58-cpp.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/cert-dcl58-cpp.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/cert-dcl58-cpp.cpp
@@ -0,0 +1,67 @@
+// RUN: %check_clang_tidy %s cert-dcl58-cpp %t -- -- -std=c++1z -I %S/Inputs/Headers
+
+#include "system-header-simulation.h"
+
+namespace A {
+  namespace B {
+    int b;
+  }
+}
+
+namespace A {
+  namespace B {
+    int c;
+  }
+}
+
+namespace posix {
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: modification of 'posix' namespace can result in undefined behavior [cert-dcl58-cpp]
+  namespace vmi {
+  }
+}
+
+namespace std {
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: modification of 'std' namespace can
+  int stdInt;
+}
+
+namespace foobar {
+  namespace std {
+    int bar;
+  }
+}
+
+namespace posix::a {
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: modification of 'posix' namespace 
+}
+
+enum class MyError {
+  ErrorA,
+  ErrorB
+};
+
+namespace std {
+template <>
+struct is_error_code_enum<MyError> : std::true_type {};
+
+template<>
+void swap<MyError>(MyError &a, MyError &b);
+}
+
+enum class MyError2 {
+  Error2A,
+  Error2B
+};
+
+namespace std {
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: modification of 'std' namespace 
+template <>
+struct is_error_code_enum<MyError2> : std::true_type {};
+
+int foobar;
+}
+
+using namespace std;
+
+int x;
+