Index: clang-tidy/CMakeLists.txt
===================================================================
--- clang-tidy/CMakeLists.txt
+++ clang-tidy/CMakeLists.txt
@@ -26,6 +26,7 @@
   )
 
 add_subdirectory(tool)
+add_subdirectory(boost)
 add_subdirectory(cert)
 add_subdirectory(llvm)
 add_subdirectory(cppcoreguidelines)
Index: clang-tidy/boost/BoostTidyModule.cpp
===================================================================
--- /dev/null
+++ clang-tidy/boost/BoostTidyModule.cpp
@@ -0,0 +1,44 @@
+//===------- BoostTidyModule.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 "../ClangTidy.h"
+#include "../ClangTidyModule.h"
+#include "../ClangTidyModuleRegistry.h"
+#include "LexicalCastRedundantTypeCheck.h"
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace boost {
+
+class ModernizeModule : public ClangTidyModule {
+public:
+  void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<LexicalCastRedundantTypeCheck>(
+        "boost-lexical-cast-redundant-type");
+  }
+
+  ClangTidyOptions getModuleOptions() override {
+    ClangTidyOptions Options;
+    return Options;
+  }
+};
+
+// Register the ModernizeTidyModule using this statically initialized variable.
+static ClangTidyModuleRegistry::Add<ModernizeModule> X("boost-module",
+                                                       "Add boost checks.");
+
+} // namespace boost
+
+// This anchor is used to force the linker to link in the generated object file
+// and thus register the BoostModule.
+volatile int BoostModuleAnchorSource = 0;
+
+} // namespace tidy
+} // namespace clang
Index: clang-tidy/boost/CMakeLists.txt
===================================================================
--- /dev/null
+++ clang-tidy/boost/CMakeLists.txt
@@ -0,0 +1,14 @@
+set(LLVM_LINK_COMPONENTS support)
+
+add_clang_library(clangTidyBoostModule
+  BoostTidyModule.cpp
+  LexicalCastRedundantTypeCheck.cpp
+
+  LINK_LIBS
+  clangAST
+  clangASTMatchers
+  clangBasic
+  clangLex
+  clangTidy
+  clangTidyUtils
+  )
Index: clang-tidy/boost/LexicalCastRedundantTypeCheck.h
===================================================================
--- /dev/null
+++ clang-tidy/boost/LexicalCastRedundantTypeCheck.h
@@ -0,0 +1,45 @@
+//===--- LexicalcastredundanttypeCheck.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_BOOST_LEXICALCASTREDUNDANTTYPE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BOOST_LEXICALCASTREDUNDANTTYPE_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace boost {
+
+/// Checks for reduntand, or different type using boost::lexical_cast
+///
+/// Given:
+/// \code
+///   int a = boost::lexical_cast<int>("42");
+///   =>
+///   auto a = boost::lexical_cast<int>("42");
+/// \code
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/boost-LexicalCastRedundantType.html
+class LexicalCastRedundantTypeCheck : public ClangTidyCheck {
+public:
+  LexicalCastRedundantTypeCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
+  void apply(const DeclStmt *D, const std::string &warning);
+};
+
+} // namespace boost
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BOOST_LEXICALCASTREDUNDANTTYPE_H
Index: clang-tidy/boost/LexicalCastRedundantTypeCheck.cpp
===================================================================
--- /dev/null
+++ clang-tidy/boost/LexicalCastRedundantTypeCheck.cpp
@@ -0,0 +1,72 @@
+//===--- LexicalcastredundanttypeCheck.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 "LexicalCastRedundantTypeCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace boost {
+
+static const std::string LEXICAL_CAST_NAME = "boost::lexical_cast";
+void LexicalCastRedundantTypeCheck::registerMatchers(MatchFinder *Finder) {
+
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(
+      declStmt(has(varDecl(hasInitializer(callExpr(callee(
+                               functionDecl(hasName(LEXICAL_CAST_NAME))))),
+                           unless(hasType(autoType())))))
+          .bind("same_type"),
+      this);
+
+  Finder->addMatcher(
+      declStmt(has(varDecl(hasInitializer(implicitCastExpr(has(callExpr(
+                   callee(functionDecl(hasName(LEXICAL_CAST_NAME))))))))))
+          .bind("different_type"),
+      this);
+}
+
+void LexicalCastRedundantTypeCheck::apply(const DeclStmt *D,
+                                          const std::string &warning) {
+  const auto *Matched = dyn_cast<VarDecl>(*D->decl_begin());
+  if (!Matched)
+    return;
+
+  Matched->getType().dump();
+  SourceRange Range(
+      Matched->getTypeSourceInfo()->getTypeLoc().getSourceRange());
+  // FIXIT: this replace doesnt work
+  diag(Range.getBegin(), warning)
+      << FixItHint::CreateReplacement(Range, "auto ");
+}
+
+void LexicalCastRedundantTypeCheck::check(
+    const MatchFinder::MatchResult &Result) {
+
+  const auto *MatchedSameType = Result.Nodes.getNodeAs<DeclStmt>("same_type");
+  const auto *MatchedDifferentType =
+      Result.Nodes.getNodeAs<DeclStmt>("different_type");
+
+  if (MatchedSameType) {
+    apply(MatchedSameType, "redundant type for lexical_cast. Use auto instead");
+  }
+  if (MatchedDifferentType) {
+    apply(MatchedDifferentType,
+          "different types for lexical_cast. Use auto instead");
+  }
+}
+
+} // namespace boost
+} // namespace tidy
+} // namespace clang
Index: clang-tidy/tool/CMakeLists.txt
===================================================================
--- clang-tidy/tool/CMakeLists.txt
+++ clang-tidy/tool/CMakeLists.txt
@@ -10,6 +10,7 @@
   clangASTMatchers
   clangBasic
   clangTidy
+  clangTidyBoostModule
   clangTidyCERTModule
   clangTidyCppCoreGuidelinesModule
   clangTidyGoogleModule
Index: clang-tidy/tool/ClangTidyMain.cpp
===================================================================
--- clang-tidy/tool/ClangTidyMain.cpp
+++ clang-tidy/tool/ClangTidyMain.cpp
@@ -393,6 +393,11 @@
 static int LLVM_ATTRIBUTE_UNUSED CERTModuleAnchorDestination =
     CERTModuleAnchorSource;
 
+// This anchor is used to force the linker to link the BoostModule.
+extern volatile int BoostModuleAnchorSource;
+static int LLVM_ATTRIBUTE_UNUSED BoostModuleAnchorDestination =
+    BoostModuleAnchorSource;
+
 // This anchor is used to force the linker to link the LLVMModule.
 extern volatile int LLVMModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED LLVMModuleAnchorDestination =
Index: docs/clang-tidy/checks/boost-LexicalCastRedundantType.rst
===================================================================
--- /dev/null
+++ docs/clang-tidy/checks/boost-LexicalCastRedundantType.rst
@@ -0,0 +1,6 @@
+.. title:: clang-tidy - boost-LexicalCastRedundantType
+
+boost-LexicalCastRedundantType
+==============================
+
+FIXME: Describe what patterns does the check detect and why. Give examples.
Index: docs/clang-tidy/checks/list.rst
===================================================================
--- docs/clang-tidy/checks/list.rst
+++ docs/clang-tidy/checks/list.rst
@@ -4,6 +4,7 @@
 =========================
 
 .. toctree::   
+   boost-LexicalCastRedundantType
    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>
Index: test/clang-tidy/boost-LexicalCastRedundantType.cpp
===================================================================
--- /dev/null
+++ test/clang-tidy/boost-LexicalCastRedundantType.cpp
@@ -0,0 +1,88 @@
+// RUN: %check_clang_tidy %s boost-lexical-cast-redundant-type %t
+
+namespace boost {
+template <typename T, typename U>
+T lexical_cast(const U &) { return T(); }
+}
+
+void same_type() {
+  // FIXME: Add something that triggers the check here.
+  int a1 = boost::lexical_cast<int>("42");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a1 = boost::lexical_cast<int>("42");
+
+  long long a2 = boost::lexical_cast<long long>("42");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a2 = boost::lexical_cast<long long>("42");
+
+  using MyType = unsigned long long;
+  MyType a3 = boost::lexical_cast<MyType>("42");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: MyType a3 = boost::lexical_cast<MyType>("42");
+
+  unsigned long long a4 = boost::lexical_cast<MyType>("2137");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a4 = boost::lexical_cast<MyType>("2137");
+
+  // multiple decls
+  int a9 = boost::lexical_cast<int>("42"), a10 = boost::lexical_cast<int>("24");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: a9 = boost::lexical_cast<int>("42"), a10 = boost::lexical_cast<int>("24");
+
+
+  MyType a11 = boost::lexical_cast<MyType>("42"), a12 = boost::lexical_cast<unsigned long long>("24");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: redundant type for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a11 = boost::lexical_cast<MyType>("42"), a12 = boost::lexical_cast<unsigned long long>("24");
+
+  unsigned long long a13 = boost::lexical_cast<unsigned long long>("42"), a14 = boost::lexical_cast<MyType>("24");
+  // CHECK-FIXES: auto a13 = boost::lexical_cast<unsigned long long>("42"), a14 = boost::lexical_cast<MyType>("24");
+
+  a13 = boost::lexical_cast<unsigned long long>("42");
+
+  int a15 = boost::lexical_cast<int>("42"), a16 = 15;
+  // CHECK-FIXES: auto a13 = boost::lexical_cast<unsigned long long>("42"), a14 = boost::lexical_cast<MyType>("24");
+
+  long long *p = boost::lexical_cast<long long*>("fdas");
+
+}
+
+void different_type() {
+  int a5 = boost::lexical_cast<long long>("1488");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: different types for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a5 = boost::lexical_cast<long long>("1488");
+
+  long long a6 = boost::lexical_cast<int>("2137");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: different types for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a6 = boost::lexical_cast<int>("2137");
+
+  using MyType = unsigned long long;
+  long long a7 = boost::lexical_cast<MyType>("42");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: different types for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a7 = boost::lexical_cast<MyType>("42");
+
+  MyType a8 = boost::lexical_cast<int>("42");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: different types for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+  // CHECK-FIXES: auto a8 = boost::lexical_cast<int>("42");
+
+  // multiple decls with different types - no fixit
+  int a9 = boost::lexical_cast<long long>("42"), a10 = boost::lexical_cast<int>("24");
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: different types for lexical_cast. Use auto instead [boost-lexical-cast-redundant-type]
+
+}
+
+// This should not generate any warnings.
+void no_warnings(int x) {
+
+  auto a4 = boost::lexical_cast<unsigned>("-42");
+  auto a5 = boost::lexical_cast<unsigned>(x);
+  auto a6 = boost::lexical_cast<int>("42"), a7 = boost::lexical_cast<int>("24");
+
+  boost::lexical_cast<int>("32");
+  no_warnings(boost::lexical_cast<unsigned>(32));
+}
+
+// FIXME: Verify the applied fix.
+//   * Make the CHECK patterns specific enough and try to make verified lines
+//     unique to avoid incorrect matches.
+
+// FIXME: Add something that doesn't trigger the check here.