Add flag for showing skipped headers in -H / --show-includes output

[hans]

Summary

Consider the following set of files:

a.cc:
#include "a.h"

a.h:
#ifndef A_H
#define A_H

#include "b.h"
#include "c.h"  // This gets "skipped".

#endif

b.h:
#ifndef B_H
#define B_H

#include "c.h"

#endif

c.h:
#ifndef C_H
#define C_H

void c();

#endif

And the output of the -H option:

$ clang -c -H a.cc
. ./a.h
.. ./b.h
... ./c.h

Note that the include of c.h in a.h is not shown in the output. (GCC does the same.) This is because of the include guard optimization: clang knows c.h is covered by an include guard which is already defined, so when it sees the include in a.h, it skips it. The same would have happened if #pragma once were used instead of include guards.

However, a.h *does* include c.h, and it may be useful to show that in the -H output. This patch adds a flag for doing that.

clang/include/clang/Driver/Options.td

 
 //===----------------------------------------------------------------------===//
 // Dependency Output Options
 //===----------------------------------------------------------------------===//
 
 def sys_header_deps : Flag<["-"], "sys-header-deps">,
   HelpText<"Include system headers in dependency output">,
   MarshallingInfoFlag<DependencyOutputOpts<"IncludeSystemHeaders">>;
+def show_skipped_includes : Flag<["-"], "show-skipped-includes">,
+  HelpText<"Show skipped includes in -H output.">,
+  DocBrief<[{#include files may be "skipped" due to include guard optimization
+             or #pragma once. This flag makes -H show also such includes.}]>,
+  MarshallingInfoFlag<DependencyOutputOpts<"ShowSkippedHeaderIncludes">>;
 def module_file_deps : Flag<["-"], "module-file-deps">,
   HelpText<"Include module files in dependency output">,
   MarshallingInfoFlag<DependencyOutputOpts<"IncludeModuleFiles">>;
 def header_include_file : Separate<["-"], "header-include-file">,
   HelpText<"Filename (or -) to write header include output to">,
   MarshallingInfoString<DependencyOutputOpts<"HeaderIncludeOutputFile">>;
 def show_includes : Flag<["--"], "show-includes">,
   HelpText<"Print cl.exe style /showIncludes to stdout">;

clang/include/clang/Frontend/DependencyOutputOptions.h

 public:
   unsigned IncludeSystemHeaders : 1; ///< Include system header dependencies.
   unsigned ShowHeaderIncludes : 1;   ///< Show header inclusions (-H).
   unsigned UsePhonyTargets : 1;      ///< Include phony targets for each
                                      /// dependency, which can avoid some 'make'
                                      /// problems.
   unsigned AddMissingHeaderDeps : 1; ///< Add missing headers to dependency list
   unsigned IncludeModuleFiles : 1; ///< Include module file dependencies.
+  unsigned ShowSkippedHeaderIncludes : 1; ///< With ShowHeaderIncludes, show
+                                          /// also includes that were skipped
+                                          /// due to the "include guard
+                                          /// optimization" or #pragma once.
 
   /// Destination of cl.exe style /showIncludes info.
   ShowIncludesDestination ShowIncludesDest = ShowIncludesDestination::None;
 
   /// The format for the dependency file.
   DependencyOutputFormat OutputFormat = DependencyOutputFormat::Make;
 
   /// The file to write dependency output to.
public:
   std::string DOTOutputFile;
 
   /// The directory to copy module dependencies to when collecting them.
   std::string ModuleDependencyOutputDir;
 
 public:
   DependencyOutputOptions()
       : IncludeSystemHeaders(0), ShowHeaderIncludes(0), UsePhonyTargets(0),
-        AddMissingHeaderDeps(0), IncludeModuleFiles(0) {}
+        AddMissingHeaderDeps(0), IncludeModuleFiles(0),
+        ShowSkippedHeaderIncludes(0) {}
 };
 
 }  // end namespace clang
 
 #endif

clang/lib/Frontend/HeaderIncludeGen.cpp

public:
   ~HeaderIncludesCallback() override {
     if (OwnsOutputFile)
       delete OutputFile;
   }
 
   void FileChanged(SourceLocation Loc, FileChangeReason Reason,
                    SrcMgr::CharacteristicKind FileType,
                    FileID PrevFID) override;
+
+  void FileSkipped(const FileEntryRef &SkippedFile, const Token &FilenameTok,
+                   SrcMgr::CharacteristicKind FileType) override;
 };
 }
 
 static void PrintHeaderInfo(raw_ostream *OutputFile, StringRef Filename,
                             bool ShowDepth, unsigned CurrentIncludeDepth,
                             bool MSStyle) {
   // Write to a temporary string to avoid unnecessary flushing on errs().
   SmallString<512> Pathname(Filename);
void HeaderIncludesCallback::FileChanged(SourceLocation Loc,
   // FIXME: Identify headers in a more robust way than comparing their name to
   // "<command line>" and "<built-in>" in a bunch of places.
   if (ShowHeader && Reason == PPCallbacks::EnterFile &&
       UserLoc.getFilename() != StringRef("<command line>")) {
     PrintHeaderInfo(OutputFile, UserLoc.getFilename(), ShowDepth, IncludeDepth,
                     MSStyle);
   }
 }
+
+void HeaderIncludesCallback::FileSkipped(const FileEntryRef &SkippedFile, const
+                                         Token &FilenameTok,
+                                         SrcMgr::CharacteristicKind FileType) {
+  if (!DepOpts.ShowSkippedHeaderIncludes)
+    return;
+
+  if (!DepOpts.IncludeSystemHeaders && isSystem(FileType))
+    return;
+
+  PrintHeaderInfo(OutputFile, SkippedFile.getName(), ShowDepth,
+                  CurrentIncludeDepth + 1, MSStyle);
+}

clang/test/Frontend/Inputs/test.h

+#ifndef TEST_H
+#define TEST_H
+
 #include "test2.h"
+#include "test2.h"
+
+#endif

clang/test/Frontend/Inputs/test2.h

+#ifndef TEST2_H
+#define TEST2_H
+
 int x;
+
+#endif

clang/test/Frontend/print-header-includes.c

 // RUN: %clang_cc1 -I%S -include Inputs/test3.h -isystem %S/Inputs/SystemHeaderPrefix \
 // RUN:     -E -H -o /dev/null %s 2> %t.stderr
 // RUN: FileCheck < %t.stderr %s
 
 // CHECK-NOT: test3.h
 // CHECK-NOT: . {{.*noline.h}}
 // CHECK: . {{.*test.h}}
 // CHECK: .. {{.*test2.h}}
+// CHECK-NOT: .. {{.*test2.h}}
+
+// RUN: %clang_cc1 -I%S -isystem %S/Inputs/SystemHeaderPrefix \
+// RUN:     -E -H -show-skipped-includes -o /dev/null %s 2> %t.stderr
+// RUN: FileCheck --check-prefix=SKIPPED < %t.stderr %s
+
+// SKIPPED-NOT: . {{.*noline.h}}
+// SKIPPED: . {{.*test.h}}
+// SKIPPED: .. {{.*test2.h}}
+// SKIPPED: .. {{.*test2.h}}
 
 // RUN: %clang_cc1 -I%S -include Inputs/test3.h -isystem %S/Inputs/SystemHeaderPrefix \
 // RUN:     -E -H -sys-header-deps -o /dev/null %s 2> %t.stderr
 // RUN: FileCheck --check-prefix SYSHEADERS < %t.stderr %s
 
 // SYSHEADERS-NOT: test3.h
 // SYSHEADERS: . {{.*noline.h}}
 // SYSHEADERS: . {{.*test.h}}