8 files changed, 51 insertions, 8 deletions
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index b74897c756b..602560ee0c5 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -429,6 +429,8 @@ def fno_cuda_approx_transcendentals : Flag<["-"], "fno-cuda-approx-transcendenta
 def dA : Flag<["-"], "dA">, Group<d_Group>;
 def dD : Flag<["-"], "dD">, Group<d_Group>, Flags<[CC1Option]>,
   HelpText<"Print macro definitions in -E mode in addition to normal output">;
+def dI : Flag<["-"], "dI">, Group<d_Group>, Flags<[CC1Option]>,
+  HelpText<"Print include directives in -E mode in addition to normal output">;
 def dM : Flag<["-"], "dM">, Group<d_Group>, Flags<[CC1Option]>,
   HelpText<"Print macro definitions in -E mode instead of normal output">;
 def dead__strip : Flag<["-"], "dead_strip">;
diff --git a/clang/include/clang/Frontend/PreprocessorOutputOptions.h b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
index f86c49039ed..3261b665380 100644
--- a/clang/include/clang/Frontend/PreprocessorOutputOptions.h
+++ b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
@@ -22,6 +22,7 @@ public:
   unsigned UseLineDirectives : 1;   ///< Use \#line instead of GCC-style \# N.
   unsigned ShowMacroComments : 1;  ///< Show comments, even in macros.
   unsigned ShowMacros : 1;         ///< Print macro definitions.
+  unsigned ShowIncludeDirectives : 1;  ///< Print includes, imports etc. within preprocessed output.
   unsigned RewriteIncludes : 1;    ///< Preprocess include directives only.
 
 public:
@@ -32,6 +33,7 @@ public:
     UseLineDirectives = 0;
     ShowMacroComments = 0;
     ShowMacros = 0;
+    ShowIncludeDirectives = 0;
     RewriteIncludes = 0;
   }
 };
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 8588fa37810..571327b806f 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2353,6 +2353,7 @@ static void ParsePreprocessorOutputArgs(PreprocessorOutputOptions &Opts,
   Opts.ShowLineMarkers = !Args.hasArg(OPT_P);
   Opts.ShowMacroComments = Args.hasArg(OPT_CC);
   Opts.ShowMacros = Args.hasArg(OPT_dM) || Args.hasArg(OPT_dD);
+  Opts.ShowIncludeDirectives = Args.hasArg(OPT_dI);
   Opts.RewriteIncludes = Args.hasArg(OPT_frewrite_includes);
   Opts.UseLineDirectives = Args.hasArg(OPT_fuse_line_directives);
 }
diff --git a/clang/lib/Frontend/PrintPreprocessedOutput.cpp b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
index 77b80e612fb..d48b952ef20 100644
--- a/clang/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -93,13 +93,16 @@ private:
   bool Initialized;
   bool DisableLineMarkers;
   bool DumpDefines;
+  bool DumpIncludeDirectives;
   bool UseLineDirectives;
   bool IsFirstFileEntered;
 public:
   PrintPPOutputPPCallbacks(Preprocessor &pp, raw_ostream &os, bool lineMarkers,
-                           bool defines, bool UseLineDirectives)
+                           bool defines, bool DumpIncludeDirectives,
+                           bool UseLineDirectives)
       : PP(pp), SM(PP.getSourceManager()), ConcatInfo(PP), OS(os),
         DisableLineMarkers(lineMarkers), DumpDefines(defines),
+        DumpIncludeDirectives(DumpIncludeDirectives),
         UseLineDirectives(UseLineDirectives) {
     CurLine = 0;
     CurFilename += "<uninit>";
@@ -320,10 +323,10 @@ void PrintPPOutputPPCallbacks::InclusionDirective(SourceLocation HashLoc,
                                                   StringRef SearchPath,
                                                   StringRef RelativePath,
                                                   const Module *Imported) {
-  // When preprocessing, turn implicit imports into @imports.
-  // FIXME: This is a stop-gap until a more comprehensive "preprocessing with
-  // modules" solution is introduced.
   if (Imported) {
+    // When preprocessing, turn implicit imports into @imports.
+    // FIXME: This is a stop-gap until a more comprehensive "preprocessing with
+    // modules" solution is introduced.
     startNewLineIfNeeded();
     MoveToLine(HashLoc);
     if (PP.getLangOpts().ObjC2) {
@@ -331,9 +334,9 @@ void PrintPPOutputPPCallbacks::InclusionDirective(SourceLocation HashLoc,
          << " /* clang -E: implicit import for \"" << File->getName()
          << "\" */";
     } else {
-      // FIXME: Preseve whether this was a
-      // #include/#include_next/#include_macros/#import.
-      OS << "#include "
+      const std::string TokenText = PP.getSpelling(IncludeTok);
+      assert(!TokenText.empty());
+      OS << "#" << TokenText << " "
          << (IsAngled ? '<' : '"')
          << FileName
          << (IsAngled ? '>' : '"')
@@ -344,6 +347,20 @@ void PrintPPOutputPPCallbacks::InclusionDirective(SourceLocation HashLoc,
     // line immediately.
     EmittedTokensOnThisLine = true;
     startNewLineIfNeeded();
+  } else {
+    // Not a module import; it's a more vanilla inclusion of some file using one
+    // of: #include, #import, #include_next, #include_macros.
+    if (DumpIncludeDirectives) {
+      startNewLineIfNeeded();
+      MoveToLine(HashLoc);
+      const std::string TokenText = PP.getSpelling(IncludeTok);
+      assert(!TokenText.empty());
+      OS << "#" << TokenText << " "
+         << (IsAngled ? '<' : '"') << FileName << (IsAngled ? '>' : '"')
+         << " /* clang -E -dI */";
+      setEmittedDirectiveOnThisLine();
+      startNewLineIfNeeded();
+    }
   }
 }
 
@@ -751,7 +768,8 @@ void clang::DoPrintPreprocessedInput(Preprocessor &PP, raw_ostream *OS,
   PP.SetCommentRetentionState(Opts.ShowComments, Opts.ShowMacroComments);
 
   PrintPPOutputPPCallbacks *Callbacks = new PrintPPOutputPPCallbacks(
-      PP, *OS, !Opts.ShowLineMarkers, Opts.ShowMacros, Opts.UseLineDirectives);
+      PP, *OS, !Opts.ShowLineMarkers, Opts.ShowMacros,
+      Opts.ShowIncludeDirectives, Opts.UseLineDirectives);
 
   // Expand macros in pragmas with -fms-extensions.  The assumption is that
   // the majority of pragmas in such a file will be Microsoft pragmas.
diff --git a/clang/test/Preprocessor/dump_import.h b/clang/test/Preprocessor/dump_import.h
new file mode 100644
index 00000000000..fded1e52cbb
--- /dev/null
+++ b/clang/test/Preprocessor/dump_import.h
@@ -0,0 +1 @@
+#define DUMP_IMPORT_TESTVAL 1
diff --git a/clang/test/Preprocessor/dump_import.m b/clang/test/Preprocessor/dump_import.m
new file mode 100644
index 00000000000..20424ad507b
--- /dev/null
+++ b/clang/test/Preprocessor/dump_import.m
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -E -dI %s -o - | FileCheck %s
+// CHECK: {{^}}#import "dump_
+
+// See also `dump_include.c` which tests other inclusion cases with `-dI`.
+
+#import "dump_import.h"
diff --git a/clang/test/Preprocessor/dump_include.c b/clang/test/Preprocessor/dump_include.c
new file mode 100644
index 00000000000..b98b5df7b77
--- /dev/null
+++ b/clang/test/Preprocessor/dump_include.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -w -E -dI -isystem %S -imacros %S/dump_include.h %s -o - | FileCheck %s
+// CHECK: {{^}}#__include_macros "/{{([^/]+/)+}}dump_
+// CHECK: {{^}}#include <dump_
+// CHECK: {{^}}#include "dump_
+// CHECK: {{^}}#include_next "dump_
+
+// See also `dump_import.m` which tests the `#import` directive with `-dI`.
+
+#include <dump_include.h>
+#include "dump_include.h"
+#include_next "dump_include.h"
diff --git a/clang/test/Preprocessor/dump_include.h b/clang/test/Preprocessor/dump_include.h
new file mode 100644
index 00000000000..9dafaa50b5c
--- /dev/null
+++ b/clang/test/Preprocessor/dump_include.h
@@ -0,0 +1,2 @@
+#pragma once
+#define DUMP_INCLUDE_TESTVAL 1