Index: clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
===================================================================
--- clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
+++ clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
@@ -45,6 +45,7 @@
 #include "StringIntegerAssignmentCheck.h"
 #include "StringLiteralWithEmbeddedNulCheck.h"
 #include "SuspiciousEnumUsageCheck.h"
+#include "SuspiciousIncludeCheck.h"
 #include "SuspiciousMemsetUsageCheck.h"
 #include "SuspiciousMissingCommaCheck.h"
 #include "SuspiciousSemicolonCheck.h"
@@ -140,6 +141,8 @@
         "bugprone-string-literal-with-embedded-nul");
     CheckFactories.registerCheck<SuspiciousEnumUsageCheck>(
         "bugprone-suspicious-enum-usage");
+    CheckFactories.registerCheck<SuspiciousIncludeCheck>(
+        "bugprone-suspicious-include");
     CheckFactories.registerCheck<SuspiciousMemsetUsageCheck>(
         "bugprone-suspicious-memset-usage");
     CheckFactories.registerCheck<SuspiciousMissingCommaCheck>(
Index: clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
===================================================================
--- clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
+++ clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
@@ -37,6 +37,7 @@
   StringIntegerAssignmentCheck.cpp
   StringLiteralWithEmbeddedNulCheck.cpp
   SuspiciousEnumUsageCheck.cpp
+  SuspiciousIncludeCheck.cpp
   SuspiciousMemsetUsageCheck.cpp
   SuspiciousMissingCommaCheck.cpp
   SuspiciousSemicolonCheck.cpp
Index: clang-tools-extra/clang-tidy/bugprone/SuspiciousIncludeCheck.h
===================================================================
--- /dev/null
+++ clang-tools-extra/clang-tidy/bugprone/SuspiciousIncludeCheck.h
@@ -0,0 +1,39 @@
+//===--- SuspiciousIncludeCheck.h - clang-tidy ------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSINCLUDECHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSINCLUDECHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace bugprone {
+
+/// Warns on inclusion of files whose names suggest that they're implementation
+/// files, instead of headers. E.g:
+///
+///     #include "foo.cpp"  // warning
+///     #include "bar.c"    // warning
+///     #include "baz.h"    // no diagnostic
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/bugprone-suspicious-include.html
+class SuspiciousIncludeCheck : public ClangTidyCheck {
+public:
+  SuspiciousIncludeCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+                           Preprocessor *ModuleExpanderPP) override;
+};
+
+} // namespace bugprone
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSINCLUDECHECK_H
Index: clang-tools-extra/clang-tidy/bugprone/SuspiciousIncludeCheck.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/clang-tidy/bugprone/SuspiciousIncludeCheck.cpp
@@ -0,0 +1,75 @@
+//===--- SuspiciousIncludeCheck.cpp - clang-tidy --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "SuspiciousIncludeCheck.h"
+#include "clang/AST/ASTContext.h"
+
+namespace clang {
+namespace tidy {
+namespace bugprone {
+
+namespace {
+class SuspiciousIncludePPCallbacks : public PPCallbacks {
+public:
+  explicit SuspiciousIncludePPCallbacks(ClangTidyCheck &Check,
+                                        const SourceManager &SM,
+                                        Preprocessor *PP)
+      : Check(Check), PP(PP) {}
+
+  void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,
+                          StringRef FileName, bool IsAngled,
+                          CharSourceRange FilenameRange, const FileEntry *File,
+                          StringRef SearchPath, StringRef RelativePath,
+                          const Module *Imported,
+                          SrcMgr::CharacteristicKind FileType) override;
+
+private:
+  ClangTidyCheck &Check;
+  Preprocessor *PP;
+};
+} // namespace
+
+void SuspiciousIncludeCheck::registerPPCallbacks(
+    const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
+  PP->addPPCallbacks(
+      ::std::make_unique<SuspiciousIncludePPCallbacks>(*this, SM, PP));
+}
+
+void SuspiciousIncludePPCallbacks::InclusionDirective(
+    SourceLocation HashLoc, const Token &IncludeTok, StringRef FileName,
+    bool IsAngled, CharSourceRange FilenameRange, const FileEntry *File,
+    StringRef SearchPath, StringRef RelativePath, const Module *Imported,
+    SrcMgr::CharacteristicKind FileType) {
+  SourceLocation DiagLoc = FilenameRange.getBegin().getLocWithOffset(1);
+
+  const char *const SuspiciousExtensions[] = {".c", ".cpp", ".cxx", ".cc"};
+  const char *const RecommendedExtensions[] = {"", ".h", ".hpp", ".hh"};
+
+  for (const char *SE : SuspiciousExtensions) {
+    if (FileName.consume_back(SE)) {
+      Check.diag(DiagLoc, "suspicious #%0 of file with %1 extension")
+          << IncludeTok.getIdentifierInfo()->getName() << SE;
+
+      for (const char *RE : RecommendedExtensions) {
+        const DirectoryLookup *CurDir;
+        Optional<FileEntryRef> File = PP->LookupFile(
+            DiagLoc, (FileName + RE).str(), IsAngled, nullptr, nullptr, CurDir,
+            nullptr, nullptr, nullptr, nullptr, nullptr);
+        if (File) {
+          Check.diag(DiagLoc, "did you mean to include '%0'?",
+                     DiagnosticIDs::Note)
+              << (FileName + RE).str();
+        }
+      }
+    }
+  }
+}
+
+} // namespace bugprone
+} // namespace tidy
+} // namespace clang
Index: clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-include.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-include.cpp
@@ -0,0 +1,21 @@
+// RUN: %check_clang_tidy %s bugprone-suspicious-include %t -- -- -isystem %S/Inputs/Headers -fmodules
+
+// CHECK-MESSAGES: [[@LINE+4]]:11: warning: suspicious #include of file with .cpp extension
+// CHECK-MESSAGES: [[@LINE+3]]:11: note: did you mean to include 'a'?
+// CHECK-MESSAGES: [[@LINE+2]]:11: note: did you mean to include 'a.h'?
+// CHECK-MESSAGES: [[@LINE+1]]:11: note: did you mean to include 'a.hpp'?
+#include "a.cpp"
+
+#include "b.h"
+
+// CHECK-MESSAGES: [[@LINE+1]]:10: warning: suspicious #import of file with .c extension
+#import "c.c"
+
+// CHECK-MESSAGES: [[@LINE+1]]:16: warning: suspicious #include_next of file with .c extension
+#include_next <c.c>
+
+// CHECK-MESSAGES: [[@LINE+1]]:13: warning: suspicious #include of file with .cc extension
+# include  <c.cc>
+
+// CHECK-MESSAGES: [[@LINE+1]]:14: warning: suspicious #include of file with .cxx extension
+#  include  <c.cxx>