[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2023-09-19 Thread Louis Dionne via Phabricator via cfe-commits 
ldionne added a comment.

I just did some digging. We completed the transition to the 
libcxx-headers-in-the-SDK already, and now upstream and downstream Clang are 
the same with respect to those search paths. I think it might just be the case 
that you need the very latest AppleClang for that to be reflected (as you know 
AppleClang always lags a bit behind). So I think there's nothing special to do 
here, upstream behaves properly and downstream will catch up automatically.


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[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2023-08-07 Thread Duncan P. N. Exon Smith via Phabricator via cfe-commits 
dexonsmith added a comment.

SGTM.


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[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2023-08-07 Thread Dmitry Polukhin via Phabricator via cfe-commits 
DmitryPolukhin added a comment.

@dexonsmith thank you for quick response. I think we need to update upstream 
behaviour to match system compiler behaviour otherwise clang-tools that uses 
path to compiler binary form CDB will not work as expected and extra options 
won't help much because it is not easy to inject in some cases. I sent 
https://reviews.llvm.org/D157283 for review. I got this change by running test 
agains system compiler and fixing it to match the real behaviour, after that I 
guessed how exactly this behaviour could be achieved.


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[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2023-08-04 Thread Duncan P. N. Exon Smith via Phabricator via cfe-commits 
dexonsmith added a comment.

I don't have access to rdar these days to look into the current state or to 
refresh my memory.

My memory is that the high-level goal was to move the libc++ headers from the 
toolchain to the SDK. For the transition, this was staged in such a way that 
they were in both locations for some period of time (internally, the transition 
may be ongoing, for all I know).

Apple clang needed to prefer the SDK, since that was the "new" place. I don't 
remember the reasoning for inverting this behaviour for LLVM clang.

- Maybe, because this way an LLVM toolchain could still override the C++ 
headers, like it could previously?
- Maybe, there was a plan to eventually switch the default in LLVM clang, but 
that got dropped/forgotten?
- Maybe, there was a plan to eventually switch the default in Apple clang, but 
that was dropped/forgotten, or the internal transition is ongoing? (This rings 
a bell. "Change LLVM clang to the desired end state, and we'll flip the 
direction temporarily in Apple clang for the duration of the transition...")

Anyway, I'm not sure the best way forward here. Perhaps clang should have a 
flag to decide which is preferred. Or perhaps LLVM clang should just change to 
match Apple clang for now.

@ldionne, thoughts?


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[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2023-08-04 Thread Dmitry Polukhin via Phabricator via cfe-commits 
DmitryPolukhin added a comment.
Herald added a subscriber: MaskRay.
Herald added a project: All.

@ldionne and @dexonsmith, it seems that this diff breaks clang-tools like 
clang-tidy and clangd if `-isysroot` is specified in the compilation database. 
Moreover, clang from Xcode 14 and 15 uses paths specified in `-sysroot` and 
ignores headers alongside the clang binary. I don’t know if it is new behavior 
or it was this way when this diff was committed. Minimal reproducer is 
following:

  $ cat compile_commands.json
  [
  {
  "directory": "/Users/test/test",
  "file": "test.cpp",
  "arguments": [
  
"/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++",
  "-isysroot",
  
"/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk",
  "-c",
  "test.cpp",
  "-v"
  ]
  }
  ]
  
  $ /build/bin/clang-tidy -p compile_commands.json test.cpp
  ...
  #include <...> search starts here:
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
   /build/lib/clang/18/include
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks
 (framework directory)
  End of search list.
  1 error generated.
  Error while processing test.cpp.
  test.cpp:1:10: error: 'cxxabi.h' file not found [clang-diagnostic-error]
  1 | #include 
|  ^~
  Found compiler error(s).
  
  $ 
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++
 -isysroot 
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk
 -c test.cpp -v
  ...
  #include <...> search starts here:
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.3/include
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
   
/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks
 (framework directory)
  End of search list.

So upstream clang-tools uses a path to the compiler binary specified in CDB as 
an installation dir and searches in 
".../XcodeDefault.xctoolchain/usr/bin/../include/c++/v1" but the Apple compiler 
from CDB searches in the path specified in sysroot 
".../MacOSX.sdk/usr/include/c++/v1". I also checked clangd from Apple 
toolchain, it also uses path species in `-sysroot`. I have a local patch that 
honors `-isysroot` if it is explicitly specified in the command line but 
prefers headers alongside the binary in other cases and it seems that it 
matches the behavior of Apple compiler.  But it breaks all tests that 
specifically test that `-isysroot` is ignored. Should I change the test and 
send the patch for review?


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[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2020-10-09 Thread Louis Dionne via Phabricator via cfe-commits 
This revision was automatically updated to reflect the committed changes.
Closed by commit rGa3a24316087d: [clang] Don't look into  
for C++ headers if they are found alongside… (authored by ldionne).

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Files:
  clang/lib/Driver/ToolChains/Darwin.cpp
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/include/c++/v1/.keep
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/lib/.keep
  clang/test/Driver/darwin-header-search-libcxx.cpp

Index: clang/test/Driver/darwin-header-search-libcxx.cpp
===
--- clang/test/Driver/darwin-header-search-libcxx.cpp
+++ clang/test/Driver/darwin-header-search-libcxx.cpp
@@ -13,39 +13,57 @@
 // RUN:   | FileCheck --check-prefix=CHECK-LIBCXX-NONE %s
 // CHECK-LIBCXX-NONE: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 
-// Check with only headers alongside the installation (those should be used,
-// but we should still add /usr/include/c++/v1 after to preserve legacy).
+// Check with only headers alongside the installation (those should be used).
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: --sysroot="" \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
 // CHECK-LIBCXX-TOOLCHAIN-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
-// CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "/usr/include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-1-NOT: "-internal-isystem" "/usr/include/c++/v1"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -isysroot %S/Inputs/basic_darwin_sdk_no_libcxx \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   -DSYSROOT=%S/Inputs/basic_darwin_sdk_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
 // CHECK-LIBCXX-TOOLCHAIN-2: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-2: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-2-NOT: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+
+// Check with only headers in the sysroot (those should be used).
+//
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN: -target x86_64-apple-darwin \
+// RUN: -stdlib=libc++ \
+// RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain_no_libcxx/usr/bin \
+// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-SYSROOT-1 %s
+// CHECK-LIBCXX-SYSROOT-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
+// CHECK-LIBCXX-SYSROOT-1: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+// CHECK-LIBCXX-SYSROOT-1-NOT: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
 
 // Check with both headers in the sysroot and headers alongside the installation
-// (the headers in  should be added after the toolchain headers).
-// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence.
+// (the headers in the toolchain should be preferred over the  headers).
+// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence
+// over --sysroot.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -resource-dir=%S/Inputs/resource_dir \
-// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr \
-// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr \
+// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
 // RUN:   -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
 // RUN:   --check-prefix=CHECK-LIBCXX-SYSROOT_AND_TOOLCHAIN-1 %s
 //
@@ -54,8 +72,8 @@
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -resource-dir=%S/Inputs/resource_dir \
-// RUN: --sysroot %S/Inputs/basic_darwin_sdk_usr \
-// RUN:   | FileCheck -D

[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2020-10-08 Thread Louis Dionne via Phabricator via cfe-commits 
ldionne updated this revision to Diff 297000.
ldionne added a comment.

Try to fix test failure on Linux


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Files:
  clang/lib/Driver/ToolChains/Darwin.cpp
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/include/c++/v1/.keep
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/lib/.keep
  clang/test/Driver/darwin-header-search-libcxx.cpp

Index: clang/test/Driver/darwin-header-search-libcxx.cpp
===
--- clang/test/Driver/darwin-header-search-libcxx.cpp
+++ clang/test/Driver/darwin-header-search-libcxx.cpp
@@ -13,39 +13,57 @@
 // RUN:   | FileCheck --check-prefix=CHECK-LIBCXX-NONE %s
 // CHECK-LIBCXX-NONE: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 
-// Check with only headers alongside the installation (those should be used,
-// but we should still add /usr/include/c++/v1 after to preserve legacy).
+// Check with only headers alongside the installation (those should be used).
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: --sysroot="" \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
 // CHECK-LIBCXX-TOOLCHAIN-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
-// CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "/usr/include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-1-NOT: "-internal-isystem" "/usr/include/c++/v1"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -isysroot %S/Inputs/basic_darwin_sdk_no_libcxx \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   -DSYSROOT=%S/Inputs/basic_darwin_sdk_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
 // CHECK-LIBCXX-TOOLCHAIN-2: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-2: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-2-NOT: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+
+// Check with only headers in the sysroot (those should be used).
+//
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN: -target x86_64-apple-darwin \
+// RUN: -stdlib=libc++ \
+// RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain_no_libcxx/usr/bin \
+// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-SYSROOT-1 %s
+// CHECK-LIBCXX-SYSROOT-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
+// CHECK-LIBCXX-SYSROOT-1: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+// CHECK-LIBCXX-SYSROOT-1-NOT: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
 
 // Check with both headers in the sysroot and headers alongside the installation
-// (the headers in  should be added after the toolchain headers).
-// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence.
+// (the headers in the toolchain should be preferred over the  headers).
+// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence
+// over --sysroot.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -resource-dir=%S/Inputs/resource_dir \
-// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr \
-// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr \
+// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
 // RUN:   -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
 // RUN:   --check-prefix=CHECK-LIBCXX-SYSROOT_AND_TOOLCHAIN-1 %s
 //
@@ -54,8 +72,8 @@
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -resource-dir=%S/Inputs/resource_dir \
-// RUN: --sysroot %S/Inputs/basic_darwin_sdk_usr \
-// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr \
+// RUN: --sysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \

[PATCH] D89001: [clang] Don't look into for C++ headers if they are found alongside the toolchain

2020-10-07 Thread Louis Dionne via Phabricator via cfe-commits 
ldionne created this revision.
ldionne added reviewers: arphaman, dexonsmith.
Herald added subscribers: cfe-commits, jkorous.
Herald added a project: clang.
ldionne requested review of this revision.

Currently, Clang looks for libc++ headers alongside the installation
directory of Clang, and it also adds a search path for headers in the
-isysroot. This is problematic if headers are found in both the toolchain
and in the sysroot, since #include_next will end up finding the libc++
headers in the sysroot instead of the intended system headers.

This patch changes the logic such that if the toolchain contains libc++
headers, no C++ header paths are added in the sysroot. However, if the
toolchain does *not* contain libc++ headers, the sysroot is searched as
usual.

This should not be a breaking change, since any code that previously
relied on some libc++ headers being found in the sysroot suffered from
the #include_next issue described above, which renders any libc++ header
basically useless.


Repository:
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https://reviews.llvm.org/D89001

Files:
  clang/lib/Driver/ToolChains/Darwin.cpp
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/include/c++/v1/.keep
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/lib/.keep
  clang/test/Driver/darwin-header-search-libcxx.cpp

Index: clang/test/Driver/darwin-header-search-libcxx.cpp
===
--- clang/test/Driver/darwin-header-search-libcxx.cpp
+++ clang/test/Driver/darwin-header-search-libcxx.cpp
@@ -13,39 +13,57 @@
 // RUN:   | FileCheck --check-prefix=CHECK-LIBCXX-NONE %s
 // CHECK-LIBCXX-NONE: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 
-// Check with only headers alongside the installation (those should be used,
-// but we should still add /usr/include/c++/v1 after to preserve legacy).
+// Check with only headers alongside the installation (those should be used).
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: --sysroot="" \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-1 %s
 // CHECK-LIBCXX-TOOLCHAIN-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
-// CHECK-LIBCXX-TOOLCHAIN-1: "-internal-isystem" "/usr/include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-1-NOT: "-internal-isystem" "/usr/include/c++/v1"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain/usr/bin \
 // RUN: -isysroot %S/Inputs/basic_darwin_sdk_no_libcxx \
-// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
+// RUN:   | FileCheck -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain \
+// RUN:   -DSYSROOT=%S/Inputs/basic_darwin_sdk_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-TOOLCHAIN-2 %s
 // CHECK-LIBCXX-TOOLCHAIN-2: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
 // CHECK-LIBCXX-TOOLCHAIN-2: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
+// CHECK-LIBCXX-TOOLCHAIN-2-NOT: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+
+// Check with only headers in the sysroot (those should be used).
+//
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN: -target x86_64-apple-darwin \
+// RUN: -stdlib=libc++ \
+// RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolchain_no_libcxx/usr/bin \
+// RUN: -isysroot %S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   | FileCheck -DSYSROOT=%S/Inputs/basic_darwin_sdk_usr_cxx_v1 \
+// RUN:   -DTOOLCHAIN=%S/Inputs/basic_darwin_toolchain_no_libcxx \
+// RUN:   --check-prefix=CHECK-LIBCXX-SYSROOT-1 %s
+// CHECK-LIBCXX-SYSROOT-1: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
+// CHECK-LIBCXX-SYSROOT-1: "-internal-isystem" "[[SYSROOT]]/usr/include/c++/v1"
+// CHECK-LIBCXX-SYSROOT-1-NOT: "-internal-isystem" "[[TOOLCHAIN]]/usr/bin/../include/c++/v1"
 
 // Check with both headers in the sysroot and headers alongside the installation
-// (the headers in  should be added after the toolchain headers).
-// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence.
+// (the headers in the toolchain should be preferred over the  headers).
+// Ensure that both -isysroot and --sysroot work, and that isysroot has precedence
+// over --sysroot.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN: -target x86_64-apple-darwin \
 // RUN: -stdlib=libc++ \
 // RUN: -ccc-install-dir %S/Inputs/basic_darwin_toolcha