[clang] [llvm] [clang] Use the VFS in `CrossTranslationUnitContext` (PR #175097)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 updated https://github.com/llvm/llvm-project/pull/175097

>From 3d88763270f0205ed50d024b249f306166518b4a Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Thu, 8 Jan 2026 15:31:32 -0800
Subject: [PATCH 1/2] [clang] Use the VFS in `CrossTranslationUnitContext`

---
 clang/lib/CrossTU/CrossTranslationUnit.cpp | 23 ++++++++++++++++++++--
 llvm/CMakeLists.txt                        |  2 +-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/clang/lib/CrossTU/CrossTranslationUnit.cpp b/clang/lib/CrossTU/CrossTranslationUnit.cpp
index a3fc2cf6bfb3c..ad2defb233a7a 100644
--- a/clang/lib/CrossTU/CrossTranslationUnit.cpp
+++ b/clang/lib/CrossTU/CrossTranslationUnit.cpp
@@ -623,7 +623,26 @@ CrossTranslationUnitContext::ASTLoader::loadFromSource(
   return CreateASTUnitFromCommandLine(
       CommandLineArgs.begin(), (CommandLineArgs.end()),
       CI.getPCHContainerOperations(), DiagOpts, Diags,
-      CI.getHeaderSearchOpts().ResourceDir);
+      CI.getHeaderSearchOpts().ResourceDir,
+      /*StorePreamblesInMemory=*/false,
+      /*PreambleStoragePath=*/StringRef(),
+      /*OnlyLocalDecls=*/false,
+      /*CaptureDiagnostics=*/CaptureDiagsKind::None,
+      /*RemappedFiles=*/{},
+      /*RemappedFilesKeepOriginalName=*/true,
+      /*PrecompilePreambleAfterNParses=*/0,
+      /*TUKind=*/TU_Complete,
+      /*CacheCodeCompletionResults=*/false,
+      /*IncludeBriefCommentsInCodeCompletion=*/false,
+      /*AllowPCHWithCompilerErrors=*/false,
+      /*SkipFunctionBodies=*/SkipFunctionBodiesScope::None,
+      /*SingleFileParse=*/false,
+      /*UserFilesAreVolatile=*/false,
+      /*ForSerialization=*/false,
+      /*RetainExcludedConditionalBlocks=*/false,
+      /*ModuleFormat=*/std::nullopt,
+      /*ErrAST=*/nullptr,
+      /*VFS=*/CI.getVirtualFileSystemPtr());
 }
 
 llvm::Expected<InvocationListTy>
@@ -710,7 +729,7 @@ llvm::Error CrossTranslationUnitContext::ASTLoader::lazyInitInvocationList() {
     return llvm::make_error<IndexError>(PreviousParsingResult);
 
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> FileContent =
-      llvm::MemoryBuffer::getFile(InvocationListFilePath);
+      CI.getVirtualFileSystem().getBufferForFile(InvocationListFilePath);
   if (!FileContent) {
     PreviousParsingResult = index_error_code::invocation_list_file_not_found;
     return llvm::make_error<IndexError>(PreviousParsingResult);
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index f0e4f5d7d6f60..467bc5ebd996c 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -697,7 +697,7 @@ else()
   option(LLVM_ENABLE_ASSERTIONS "Enable assertions" ON)
 endif()
 
-option(LLVM_ENABLE_IO_SANDBOX "Enable IO sandboxing in supported tools" OFF)
+option(LLVM_ENABLE_IO_SANDBOX "Enable IO sandboxing in supported tools" ON) # TODO: Set to OFF before merging.
 option(LLVM_ENABLE_EXPENSIVE_CHECKS "Enable expensive checks" OFF)
 
 set(LLVM_ABI_BREAKING_CHECKS "WITH_ASSERTS" CACHE STRING

>From 522c8686cee66830fe823e11ed4568f4efc255b6 Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Fri, 9 Jan 2026 09:41:16 -0800
Subject: [PATCH 2/2] Fix Linux distro detection earlier

---
 clang/lib/CrossTU/CrossTranslationUnit.cpp | 24 ++++------------------
 1 file changed, 4 insertions(+), 20 deletions(-)

diff --git a/clang/lib/CrossTU/CrossTranslationUnit.cpp b/clang/lib/CrossTU/CrossTranslationUnit.cpp
index ad2defb233a7a..7496deb74cb67 100644
--- a/clang/lib/CrossTU/CrossTranslationUnit.cpp
+++ b/clang/lib/CrossTU/CrossTranslationUnit.cpp
@@ -24,6 +24,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/IOSandbox.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/YAMLParser.h"
@@ -620,29 +621,12 @@ CrossTranslationUnitContext::ASTLoader::loadFromSource(
   auto Diags = llvm::makeIntrusiveRefCnt<DiagnosticsEngine>(DiagID, *DiagOpts,
                                                             DiagClient);
 
+  // This runs the driver which isn't expected to be free of sandbox violations.
+  auto BypassSandbox = llvm::sys::sandbox::scopedDisable();
   return CreateASTUnitFromCommandLine(
       CommandLineArgs.begin(), (CommandLineArgs.end()),
       CI.getPCHContainerOperations(), DiagOpts, Diags,
-      CI.getHeaderSearchOpts().ResourceDir,
-      /*StorePreamblesInMemory=*/false,
-      /*PreambleStoragePath=*/StringRef(),
-      /*OnlyLocalDecls=*/false,
-      /*CaptureDiagnostics=*/CaptureDiagsKind::None,
-      /*RemappedFiles=*/{},
-      /*RemappedFilesKeepOriginalName=*/true,
-      /*PrecompilePreambleAfterNParses=*/0,
-      /*TUKind=*/TU_Complete,
-      /*CacheCodeCompletionResults=*/false,
-      /*IncludeBriefCommentsInCodeCompletion=*/false,
-      /*AllowPCHWithCompilerErrors=*/false,
-      /*SkipFunctionBodies=*/SkipFunctionBodiesScope::None,
-      /*SingleFileParse=*/false,
-      /*UserFilesAreVolatile=*/false,
-      /*ForSerialization=*/false,
-      /*RetainExcludedConditionalBlocks=*/false,
-      /*ModuleFormat=*/std::nullopt,
-      /*ErrAST=*/nullptr,
-      /*VFS=*/CI.getVirtualFileSystemPtr());
+      CI.getHeaderSearchOpts().ResourceDir);
 }
 
 llvm::Expected<InvocationListTy>