[clang] [clang][driver] Add \<executable\>/../include/c++/v1 to include path on Darwin (PR #70817)

[Liviu Ionescu via cfe-commits]

https://github.com/ilg-ul created https://github.com/llvm/llvm-project/pull/70817

On macOS, when clang is invoked via a symlink, since the InstalledDir is where the link is located, the C++ headers are not identified and the default system headers are used.

```console
% ln -s /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/bin/clang++ ~/tmp/clang++
%  ~/tmp/clang++ -v hello.cpp -stdlib=libc++
xPack x86_64 clang version 15.0.7 (https://github.com/xpack-dev-tools/clang-xpack 9b1ff65945b1aaddfe7c0c4d99001ebca5d67b03)
Target: x86_64-apple-darwin21.6.0
Thread model: posix

InstalledDir: /Users/ilg/tmp/. <--- !!!
ignoring nonexistent directory "/Users/ilg/tmp/./../include/c++/v1" <--- !!!

 "/Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/bin/clang-15" -cc1 -triple x86_64-apple-macosx12.0.0 -Wundef-prefix=TARGET_OS_ -Werror=undef-prefix -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name hello.cpp -mrelocation-model pic -pic-level 2 -mframe-pointer=all -ffp-contract=on -fno-rounding-math -funwind-tables=2 -fcompatibility-qualified-id-block-type-checking -fvisibility-inlines-hidden-static-local-var -target-cpu penryn -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=lldb -target-linker-version 409.12 -v -fcoverage-compilation-dir=/Users/ilg/tmp -resource-dir /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/lib/clang/15.0.7 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -stdlib=libc++ -internal-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1 -internal-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include -internal-isystem /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/lib/clang/15.0.7/include -internal-externc-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -fdeprecated-macro -fdebug-compilation-dir=/Users/ilg/tmp -ferror-limit 19 -stack-protector 1 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fmax-type-align=16 -fcolor-diagnostics -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /var/folders/gr/13tt3vcd7m1gnbhwtkmf5cnw0000gn/T/hello-a87934.o -x c++ hello.cpp
clang -cc1 version 15.0.7 based upon LLVM 15.0.7 default target x86_64-apple-darwin21.6.0
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include"
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:

 /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1 <--- Wrong!

 /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/lib/clang/15.0.7/include
 /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include
 /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
End of search list.
 "/usr/bin/ld" -demangle -lto_library /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 12.0.0 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -o a.out /var/folders/gr/13tt3vcd7m1gnbhwtkmf5cnw0000gn/T/hello-a87934.o -lc++ -lSystem /Users/ilg/Library/xPacks/@xpack-dev-tools/clang/15.0.7-3.1/.content/lib/clang/15.0.7/lib/darwin/libclang_rt.osx.a
```

Using the system headers instead of the toolchain headers may have very subtle consequences, sometimes leading to compile errors which are hard to diagnose.

This fix adds a second check using the folder where the executable is located.

>From 7fbc229ee7316d826517480ee7896c91dad941f3 Mon Sep 17 00:00:00 2001
From: Liviu Ionescu <ilg at livius.net>
Date: Tue, 31 Oct 2023 17:09:04 +0200
Subject: [PATCH] Add \<executable\>/../include/c++/v1 to include path

On macOS, when clang is invoked via a symlink, since the InstalledDir is
where the link is located, the C++ headers are not identified and the
default system headers are used.

This fix adds a second check using the folder where the executable is
located.
---
 clang/lib/Driver/ToolChains/Darwin.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index f28e08d81bf29b4..de55307385966cf 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -2494,6 +2494,19 @@ void DarwinClang::AddClangCXXStdlibIncludeArgs(
                    << "\"\n";
     }
 
+    // Check for the folder where the executable is located, if different.
+    if (getDriver().getInstalledDir() != getDriver().Dir) {
+      InstallBin = llvm::StringRef(getDriver().Dir.c_str());
+      llvm::sys::path::append(InstallBin, "..", "include", "c++", "v1");
+      if (getVFS().exists(InstallBin)) {
+        addSystemInclude(DriverArgs, CC1Args, InstallBin);
+        return;
+      } else if (DriverArgs.hasArg(options::OPT_v)) {
+        llvm::errs() << "ignoring nonexistent directory \"" << InstallBin
+                     << "\"\n";
+      }
+    }
+
     // Otherwise, check for (2)
     llvm::SmallString<128> SysrootUsr = Sysroot;
     llvm::sys::path::append(SysrootUsr, "usr", "include", "c++", "v1");