Try to shorten system header paths when using -MD depfiles

GCC tries to shorten system headers in depfiles using its real path
(resolving components like ".." and following symlinks). Mimic this
feature to ensure that the Ninja build tool detects the correct
dependencies when a symlink changes directory levels, see
https://github.com/ninja-build/ninja/issues/1330

An option to disable this feature is added in case "these changed header
paths may conflict with some compilation environments", see
https://gcc.gnu.org/ml/gcc-patches/2012-09/msg00287.html

Note that the original feature request for GCC
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52974) also included paths
preprocessed output (-E) and diagnostics. That is not implemented now
since I am not sure if it breaks something else.

Differential Revision: https://reviews.llvm.org/D37954

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316193 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Driver/Options.td

@@ -384,6 +384,11 @@ def MT : JoinedOrSeparate<["-"], "MT">, Group<M_Group>, Flags<[CC1Option]>,
     HelpText<"Specify name of main file output in depfile">;
 def MV : Flag<["-"], "MV">, Group<M_Group>, Flags<[CC1Option]>,
     HelpText<"Use NMake/Jom format for the depfile">;
+def fno_canonical_system_headers : Flag<["-"], "fno-canonical-system-headers">,
+    Group<M_Group>, Flags<[CC1Option]>,
+    HelpText<"Do not shorten system header paths in depfiles">;
+def fcanonical_system_headers : Flag<["-"], "fcanonical-system-headers">,
+    Group<M_Group>;
 def Mach : Flag<["-"], "Mach">, Group<Link_Group>;
 def O0 : Flag<["-"], "O0">, Group<O_Group>, Flags<[CC1Option, HelpHidden]>;
 def O4 : Flag<["-"], "O4">, Group<O_Group>, Flags<[CC1Option, HelpHidden]>;

include/clang/Frontend/DependencyOutputOptions.h

@@ -30,6 +30,8 @@ public:
   unsigned AddMissingHeaderDeps : 1; ///< Add missing headers to dependency list
   unsigned PrintShowIncludes : 1; ///< Print cl.exe style /showIncludes info.
   unsigned IncludeModuleFiles : 1; ///< Include module file dependencies.
+  unsigned CanonicalSystemHeaders : 1; ///< Try to output a shorter path for
+                                       /// system header dependencies.
 
   /// The format for the dependency file.
   DependencyOutputFormat OutputFormat;
@@ -67,6 +69,7 @@ public:
     AddMissingHeaderDeps = 0;
     PrintShowIncludes = 0;
     IncludeModuleFiles = 0;
+    CanonicalSystemHeaders = 1;
     OutputFormat = DependencyOutputFormat::Make;
   }
 };

lib/Driver/Job.cpp

@@ -73,8 +73,8 @@ static bool skipArgs(const char *Flag, bool HaveCrashVFS, int &SkipNum,
 
   // These flags are all of the form -Flag and have no second argument.
   ShouldSkip = llvm::StringSwitch<bool>(Flag)
-    .Cases("-M", "-MM", "-MG", "-MP", "-MD", true)
-    .Case("-MMD", true)
+    .Cases("-M", "-MM", "-MG", "-MP", "-MD", "-MMD", true)
+    .Cases("-fno-canonical-system-headers", "-fcanonical-system-headers", true)
     .Default(false);
 
   // Match found.

lib/Driver/ToolChains/Clang.cpp

@@ -964,6 +964,13 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_C);
   Args.AddLastArg(CmdArgs, options::OPT_CC);
 
+  if (Arg *A = Args.getLastArg(options::OPT_fno_canonical_system_headers,
+                               options::OPT_fcanonical_system_headers)) {
+    if (A->getOption().matches(options::OPT_fno_canonical_system_headers)) {
+      CmdArgs.push_back("-fno-canonical-system-headers");
+    }
+  }
+
   // Handle dependency file generation.
   if ((A = Args.getLastArg(options::OPT_M, options::OPT_MM)) ||
       (A = Args.getLastArg(options::OPT_MD)) ||

lib/Frontend/CompilerInvocation.cpp

@@ -1002,6 +1002,7 @@ static void ParseDependencyOutputArgs(DependencyOutputOptions &Opts,
   Opts.Targets = Args.getAllArgValues(OPT_MT);
   Opts.IncludeSystemHeaders = Args.hasArg(OPT_sys_header_deps);
   Opts.IncludeModuleFiles = Args.hasArg(OPT_module_file_deps);
+  Opts.CanonicalSystemHeaders = !Args.hasArg(OPT_fno_canonical_system_headers);
   Opts.UsePhonyTargets = Args.hasArg(OPT_MP);
   Opts.ShowHeaderIncludes = Args.hasArg(OPT_H);
   Opts.HeaderIncludeOutputFile = Args.getLastArgValue(OPT_header_include_file);

lib/Frontend/DependencyFile.cpp

@@ -161,6 +161,7 @@ class DFGImpl : public PPCallbacks {
   bool AddMissingHeaderDeps;
   bool SeenMissingHeader;
   bool IncludeModuleFiles;
+  bool CanonicalSystemHeaders;
   DependencyOutputFormat OutputFormat;
 
 private:
@@ -176,6 +177,7 @@ public:
       AddMissingHeaderDeps(Opts.AddMissingHeaderDeps),
       SeenMissingHeader(false),
       IncludeModuleFiles(Opts.IncludeModuleFiles),
+      CanonicalSystemHeaders(Opts.CanonicalSystemHeaders),
       OutputFormat(Opts.OutputFormat) {
     for (const auto &ExtraDep : Opts.ExtraDeps) {
       AddFilename(ExtraDep);
@@ -288,6 +290,15 @@ void DFGImpl::FileChanged(SourceLocation Loc,
   if (!FileMatchesDepCriteria(Filename.data(), FileType))
     return;
 
+  // Try to shorten system header paths like GCC does (unless
+  // -fno-canonical-system-headers is given).
+  if (CanonicalSystemHeaders && isSystem(FileType)) {
+    StringRef RealPath = FE->tryGetRealPathName();
+    if (!RealPath.empty() && RealPath.size() < Filename.size()) {
+      Filename = RealPath;
+    }
+  }
+
   AddFilename(llvm::sys::path::remove_leading_dotslash(Filename));
 }
 

lib/Tooling/ArgumentsAdjusters.cpp

@@ -58,7 +58,9 @@ ArgumentsAdjuster getClangStripDependencyFileAdjuster() {
       StringRef Arg = Args[i];
       // All dependency-file options begin with -M. These include -MM,
       // -MF, -MG, -MP, -MT, -MQ, -MD, and -MMD.
-      if (!Arg.startswith("-M"))
+      // The exception is -f[no-]canonical-system-headers.
+      if (!Arg.startswith("-M") && Arg != "-fno-canonical-system-headers" &&
+          Arg != "-fcanonical-system-headers")
         AdjustedArgs.push_back(Args[i]);
 
       if ((Arg == "-MF") || (Arg == "-MT") || (Arg == "-MQ") ||

test/Preprocessor/dependencies-realpath.c

@@ -0,0 +1,33 @@
+// RUN: mkdir -p %t/sub/dir
+// RUN: echo > %t/sub/empty.h
+
+// Test that system header paths are expanded
+//
+// RUN: %clang -fsyntax-only -MD -MF %t.d -MT foo %s -isystem %t/sub/dir/..
+// RUN: FileCheck -check-prefix=TEST1 %s < %t.d
+// TEST1: foo:
+// TEST1: sub{{/|\\}}empty.h
+
+// Test that system header paths are not expanded to a longer form
+//
+// RUN: cd %t && %clang -fsyntax-only -MD -MF %t.d -MT foo %s -isystem sub/dir/..
+// RUN: FileCheck -check-prefix=TEST2 %s < %t.d
+// TEST2: foo:
+// TEST2: sub/dir/..{{/|\\}}empty.h
+
+// Test that user header paths are not expanded
+//
+// RUN: %clang -fsyntax-only -MD -MF %t.d -MT foo %s -I %t/sub/dir/..
+// RUN: FileCheck -check-prefix=TEST3 %s < %t.d
+// TEST3: foo:
+// TEST3: sub/dir/..{{/|\\}}empty.h
+
+// Test that system header paths are not expanded with -fno-canonical-system-headers
+// (and also that the -fsystem-system-headers option is accepted)
+//
+// RUN: %clang -fsyntax-only -MD -MF %t.d -MT foo %s -I %t/sub/dir/.. -fcanonical-system-headers -fno-canonical-system-headers
+// RUN: FileCheck -check-prefix=TEST4 %s < %t.d
+// TEST4: foo:
+// TEST4: sub/dir/..{{/|\\}}empty.h
+
+#include <empty.h>