[Driver] Fix libcxx detection on Darwin with clang run as ./clang

[ilya-biryukov]

Summary

By using '..' instead of fs::parent_path.

The intention of the code was to go from 'path/to/clang/bin' to
'path/to/clang/include'. In most cases parent_path works, however it
would fail when clang is run as './clang'.

This was noticed in Chromium's bug tracker, see
https://bugs.chromium.org/p/chromium/issues/detail?id=919761

[arphaman]

That makes sense, LGTM. Thanks!

[thakis]

…can you land this? :-)

[ilya-biryukov]

Sorry about the delay.

lib/Driver/ToolChains/Darwin.cpp

void DarwinClang::AddClangCXXStdlibIncludeArgs(
 
   switch (GetCXXStdlibType(DriverArgs)) {
   case ToolChain::CST_Libcxx: {
     llvm::StringRef InstallDir = getDriver().getInstalledDir();
     if (InstallDir.empty())
       break;
     // On Darwin, libc++ may be installed alongside the compiler in
     // include/c++/v1.
-    // Get from 'foo/bin' to 'foo'.
-    SmallString<128> P = llvm::sys::path::parent_path(InstallDir);
-    // Get to 'foo/include/c++/v1'.
-    llvm::sys::path::append(P, "include", "c++", "v1");
+    // Get from 'foo/bin' to 'foo/include/c++/v1'.
+    SmallString<128> P = InstallDir;
+    // Note that InstallDir can be relative, so we have to '..' and not
+    // parent_path.
+    llvm::sys::path::append(P, "..", "include", "c++", "v1");
     addSystemInclude(DriverArgs, CC1Args, P);
     break;
   }
   case ToolChain::CST_Libstdcxx:
     // FIXME: should we do something about it?
     break;
   }
 }

test/Driver/darwin-stdlib.cpp

 // This test will fail if CLANG_DEFAULT_CXX_STDLIB is set to anything different
 // than the platform default. (see https://llvm.org/bugs/show_bug.cgi?id=30548)
 // XFAIL: default-cxx-stdlib-set
 
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch arm64 -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.8 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -mmacosx-version-min=10.9 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=6.1 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBSTDCXX
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7s -miphoneos-version-min=7.0 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
 // RUN: %clang -target x86_64-apple-darwin -ccc-install-dir %S/Inputs/darwin_toolchain_tree/bin/ -arch armv7k %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LIBCXX
 
 // The purpose of this test is that the libc++ headers should be found
 // properly. We also pass -stdlib=libc++ to make sure the logic to add the
 // optional absolute include for libc++ from InitHeaderSearch.cpp also fires.
 
 // CHECK-LIBCXX: "-stdlib=libc++"
-// CHECK-LIBCXX: "-internal-isystem" "{{[^"]*}}{{/|\\\\}}Inputs{{/|\\\\}}darwin_toolchain_tree{{/|\\\\}}bin{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}v1"
+// CHECK-LIBCXX: "-internal-isystem" "{{[^"]*}}{{/|\\\\}}Inputs{{/|\\\\}}darwin_toolchain_tree{{/|\\\\}}bin{{/|\\\\}}..{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}v1"
 
 // CHECK-LIBSTDCXX-NOT: -stdlib=libc++
 // CHECK-LIBSTDCXX-NOT: -stdlib=libstdc++
 // CHECK-LIBSTDCXX-NOT: -internal-isystem

test/Tooling/Inputs/mock-libcxx/bin/clang

+This file is a placeholder to keep its parent directory in git.