Reapplying r246209, which exposed language options to the checkers. This time disable UseNullptrCheck when not compiling in C++ mode, but still allow in C++11 mode since it's likely the user wishes to modernize their code.

llvm-svn: 246298
diff --git a/clang-tools-extra/clang-tidy/ClangTidy.h b/clang-tools-extra/clang-tidy/ClangTidy.h
index 2df17c2..a2dbcbc 100644
--- a/clang-tools-extra/clang-tidy/ClangTidy.h
+++ b/clang-tools-extra/clang-tidy/ClangTidy.h
@@ -158,6 +158,8 @@
   OptionsView Options;
   /// \brief Returns the main file name of the current translation unit.
   StringRef getCurrentMainFile() const { return Context->getCurrentFile(); }
+  /// \brief Returns the language options from the context.
+  LangOptions getLangOpts() const { return Context->getLangOpts(); }
 };
 
 class ClangTidyCheckFactories;
diff --git a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
index c383440..e19011b 100644
--- a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
+++ b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
@@ -212,6 +212,7 @@
 
 void ClangTidyContext::setASTContext(ASTContext *Context) {
   DiagEngine->SetArgToStringFn(&FormatASTNodeDiagnosticArgument, Context);
+  LangOpts = Context->getLangOpts();
 }
 
 const ClangTidyGlobalOptions &ClangTidyContext::getGlobalOptions() const {
diff --git a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
index f1ab494..a452d68 100644
--- a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
+++ b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
@@ -149,6 +149,9 @@
   /// \brief Sets ASTContext for the current translation unit.
   void setASTContext(ASTContext *Context);
 
+  /// \brief Gets the language options from the AST context
+  LangOptions getLangOpts() const { return LangOpts; }
+
   /// \brief Returns the name of the clang-tidy check which produced this
   /// diagnostic ID.
   StringRef getCheckName(unsigned DiagnosticID) const;
@@ -198,6 +201,8 @@
   ClangTidyOptions CurrentOptions;
   std::unique_ptr<GlobList> CheckFilter;
 
+  LangOptions LangOpts;
+
   ClangTidyStats Stats;
 
   llvm::DenseMap<unsigned, std::string> CheckNamesByDiagnosticID;
diff --git a/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
index ea3bd950..08d6c98 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
@@ -453,7 +453,11 @@
 }
 
 void UseNullptrCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(makeCastSequenceMatcher(), this);
+  // Only register the matcher for C++. Because this checker is used for
+  // modernization, it is reasonable to run it on any C++ standard with the
+  // assumption the user is trying to modernize their codebase.
+  if (getLangOpts().CPlusPlus)
+    Finder->addMatcher(makeCastSequenceMatcher(), this);
 }
 
 void UseNullptrCheck::check(const MatchFinder::MatchResult &Result) {