[clangd] Use TargetOpts from preamble when building ASTs (#88381)

Building ASTs with compile flags that are incompatible to the ones used
for the Preamble are not really supported by clang and can trigger
crashes.

In an ideal world, we should be re-using not only TargetOpts, but the
full ParseInputs from the Preamble to prevent such failures.

Unfortunately current contracts of ThreadSafeFS makes this a non-safe
change for certain implementations. As there are no guarantees that the
same ThreadSafeFS is going to be valid in the Context::current() we're
building the AST in.

clang-tools-extra/clangd/Preamble.cpp

@@ -700,6 +700,7 @@ buildPreamble(PathRef FileName, CompilerInvocation CI,
     Result->Marks = CapturedInfo.takeMarks();
     Result->StatCache = StatCache;
     Result->MainIsIncludeGuarded = CapturedInfo.isMainFileIncludeGuarded();
+    Result->TargetOpts = CI.TargetOpts;
     if (PreambleCallback) {
       trace::Span Tracer("Running PreambleCallback");
       auto Ctx = CapturedInfo.takeLife();
@@ -913,6 +914,12 @@ PreamblePatch PreamblePatch::createMacroPatch(llvm::StringRef FileName,
 }
 
 void PreamblePatch::apply(CompilerInvocation &CI) const {
+  // Make sure the compilation uses same target opts as the preamble. Clang has
+  // no guarantees around using arbitrary options when reusing PCHs, and
+  // different target opts can result in crashes, see
+  // ParsedASTTest.PreambleWithDifferentTarget.
+  CI.TargetOpts = Baseline->TargetOpts;
+
   // No need to map an empty file.
   if (PatchContents.empty())
     return;

clang-tools-extra/clangd/Preamble.h

@@ -30,6 +30,7 @@
 #include "clang-include-cleaner/Record.h"
 #include "support/Path.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/TargetOptions.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/PrecompiledPreamble.h"
 #include "clang/Lex/Lexer.h"
@@ -97,6 +98,10 @@ struct PreambleData {
   // Version of the ParseInputs this preamble was built from.
   std::string Version;
   tooling::CompileCommand CompileCommand;
+  // Target options used when building the preamble. Changes in target can cause
+  // crashes when deserializing preamble, this enables consumers to use the
+  // same target (without reparsing CompileCommand).
+  std::shared_ptr<TargetOptions> TargetOpts = nullptr;
   PrecompiledPreamble Preamble;
   std::vector<Diag> Diags;
   // Processes like code completions and go-to-definitions will need #include

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

@@ -4160,7 +4160,32 @@ TEST(CompletionTest, DoNotCrash) {
     auto Completions = completions(Case);
   }
 }
+TEST(CompletionTest, PreambleFromDifferentTarget) {
+  constexpr std::string_view PreambleTarget = "x86_64";
+  constexpr std::string_view Contents =
+      "int foo(int); int num; int num2 = foo(n^";
 
+  Annotations Test(Contents);
+  auto TU = TestTU::withCode(Test.code());
+  TU.ExtraArgs.emplace_back("-target");
+  TU.ExtraArgs.emplace_back(PreambleTarget);
+  auto Preamble = TU.preamble();
+  ASSERT_TRUE(Preamble);
+  // Switch target to wasm.
+  TU.ExtraArgs.pop_back();
+  TU.ExtraArgs.emplace_back("wasm32");
+
+  MockFS FS;
+  auto Inputs = TU.inputs(FS);
+  auto Result = codeComplete(testPath(TU.Filename), Test.point(),
+                             Preamble.get(), Inputs, {});
+  auto Signatures =
+      signatureHelp(testPath(TU.Filename), Test.point(), *Preamble, Inputs, {});
+
+  // Make sure we don't crash.
+  EXPECT_THAT(Result.Completions, Not(testing::IsEmpty()));
+  EXPECT_THAT(Signatures.signatures, Not(testing::IsEmpty()));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang

clang-tools-extra/clangd/unittests/ParsedASTTests.cpp

@@ -12,10 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "../../clang-tidy/ClangTidyCheck.h"
-#include "../../clang-tidy/ClangTidyModule.h"
-#include "../../clang-tidy/ClangTidyModuleRegistry.h"
 #include "AST.h"
-#include "CompileCommands.h"
 #include "Compiler.h"
 #include "Config.h"
 #include "Diagnostics.h"
@@ -32,7 +29,6 @@
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TokenKinds.h"
-#include "clang/Lex/PPCallbacks.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Testing/Annotations/Annotations.h"
@@ -41,6 +37,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <memory>
+#include <string_view>
 #include <utility>
 #include <vector>
 
@@ -347,9 +344,8 @@ TEST(ParsedASTTest, CollectsMainFileMacroExpansions) {
   }
   for (const auto &R : AST.getMacros().UnknownMacros)
     MacroExpansionPositions.push_back(R.StartOffset);
-  EXPECT_THAT(
-      MacroExpansionPositions,
-      testing::UnorderedElementsAreArray(TestCase.points()));
+  EXPECT_THAT(MacroExpansionPositions,
+              testing::UnorderedElementsAreArray(TestCase.points()));
 }
 
 MATCHER_P(withFileName, Inc, "") { return arg.FileName == Inc; }
@@ -768,6 +764,35 @@ main:
       << "Should not try to build AST for assembly source file";
 }
 
+TEST(ParsedASTTest, PreambleWithDifferentTarget) {
+  constexpr std::string_view kPreambleTarget = "x86_64";
+  // Specifically picking __builtin_va_list as it triggers crashes when
+  // switching to wasm.
+  // It's due to different predefined types in different targets.
+  auto TU = TestTU::withHeaderCode("void foo(__builtin_va_list);");
+  TU.Code = "void bar() { foo(2); }";
+  TU.ExtraArgs.emplace_back("-target");
+  TU.ExtraArgs.emplace_back(kPreambleTarget);
+  const auto Preamble = TU.preamble();
+
+  // Switch target to wasm.
+  TU.ExtraArgs.pop_back();
+  TU.ExtraArgs.emplace_back("wasm32");
+
+  IgnoreDiagnostics Diags;
+  MockFS FS;
+  auto Inputs = TU.inputs(FS);
+  auto CI = buildCompilerInvocation(Inputs, Diags);
+  ASSERT_TRUE(CI) << "Failed to build compiler invocation";
+
+  auto AST = ParsedAST::build(testPath(TU.Filename), std::move(Inputs),
+                              std::move(CI), {}, Preamble);
+
+  ASSERT_TRUE(AST);
+  // We use the target from preamble, not with the most-recent flags.
+  EXPECT_EQ(AST->getASTContext().getTargetInfo().getTriple().getArchName(),
+            llvm::StringRef(kPreambleTarget));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang