[clang] [ToolChains/NetBSD] Support relative libc++ header path

Support locating the libc++ header files relatively to the clang
executable, in addition to the default system path.  This is meant
to cover two use cases: running just-built clang from the install
directory, and running installed clang from non-standard location
(e.g. /usr/local).

This is the first step towards ensuring that tests of more LLVM projects
can work out-of-the-box within the build tree, and use the correct set
of headers (rather than e.g. mixing just-built clang+libcxx with system
install of libcxx).  It avoids requiring the user to hack around missing
include paths, or LLVM build system to replicate system-specific C++
library defaults in order to append appropriate paths implicitly.

Differential Revision: https://reviews.llvm.org/D58592

llvm-svn: 355282

1 files changed, 18 insertions, 2 deletions

diff --git a/clang/lib/Driver/ToolChains/NetBSD.cpp b/clang/lib/Driver/ToolChains/NetBSD.cpp
index ae9564b817c..53587e27853 100644
--- a/clang/lib/Driver/ToolChains/NetBSD.cpp
+++ b/clang/lib/Driver/ToolChains/NetBSD.cpp
@@ -16,6 +16,7 @@
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
@@ -422,8 +423,23 @@ ToolChain::CXXStdlibType NetBSD::GetDefaultCXXStdlibType() const {
 
 void NetBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                    llvm::opt::ArgStringList &CC1Args) const {
-  addSystemInclude(DriverArgs, CC1Args,
-                   getDriver().SysRoot + "/usr/include/c++/");
+  const std::string Candidates[] = {
+    // directory relative to build tree
+    getDriver().Dir + "/../include/c++/v1",
+    // system install with full upstream path
+    getDriver().SysRoot + "/usr/include/c++/v1",
+    // system install from src
+    getDriver().SysRoot + "/usr/include/c++",
+  };
+
+  for (const auto &IncludePath : Candidates) {
+    if (!getVFS().exists(IncludePath + "/__config"))
+      continue;
+
+    // Use the first candidate that looks valid.
+    addSystemInclude(DriverArgs, CC1Args, IncludePath);
+    return;
+  }
 }
 
 void NetBSD::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,