From 00a3c9f2a46a566b3ff10f2d24b01426df2193ab Mon Sep 17 00:00:00 2001
From: Sam McCall <sam.mccall@gmail.com>
Date: Sat, 7 May 2022 02:15:41 +0200
Subject: [PATCH] [Frontend] Flip default of
 CreateInvocationOptions::ProbePrecompiled to false

This is generally a better default for tools other than the compiler, which
shouldn't assume a PCH file on disk is something they can consume.

Preserve the old behavior in places associated with libclang/c-index-test
(including ASTUnit) as there are tests relying on it and most important
consumers are out-of-tree. It's unclear whether the tests are specifically
trying to test this functionality, and what the downstream implications of
removing it are. Hopefully someone more familiar can clean this up in future.

Differential Revision: https://reviews.llvm.org/D125149
---
 clang/include/clang/Frontend/Utils.h   |  2 +-
 clang/lib/Frontend/ASTUnit.cpp         |  1 +
 clang/tools/c-index-test/core_main.cpp |  1 +
 clang/tools/libclang/Indexing.cpp      |  1 +
 clang/unittests/Frontend/UtilsTest.cpp | 14 +++++++-------
 5 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/clang/include/clang/Frontend/Utils.h b/clang/include/clang/Frontend/Utils.h
index 1e8841429ffa..240624d5408f 100644
--- a/clang/include/clang/Frontend/Utils.h
+++ b/clang/include/clang/Frontend/Utils.h
@@ -206,7 +206,7 @@ struct CreateInvocationOptions {
   /// This is used to replace -include with -include-pch in the cc1 args.
   /// FIXME: ProbePrecompiled=true is a poor, historical default.
   /// It misbehaves if the PCH file is from GCC, has the wrong version, etc.
-  bool ProbePrecompiled = true;
+  bool ProbePrecompiled = false;
   /// If set, the target is populated with the cc1 args produced by the driver.
   /// This may be populated even if createInvocation returns nullptr.
   std::vector<std::string> *CC1Args = nullptr;
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 1d0f472e9c6e..1cf20a0b662a 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -1732,6 +1732,7 @@ ASTUnit *ASTUnit::LoadFromCommandLine(
     CreateInvocationOptions CIOpts;
     CIOpts.VFS = VFS;
     CIOpts.Diags = Diags;
+    CIOpts.ProbePrecompiled = true; // FIXME: historical default. Needed?
     CI = createInvocation(llvm::makeArrayRef(ArgBegin, ArgEnd),
                           std::move(CIOpts));
     if (!CI)
diff --git a/clang/tools/c-index-test/core_main.cpp b/clang/tools/c-index-test/core_main.cpp
index c5f47baa8458..ea15b2bcd5c2 100644
--- a/clang/tools/c-index-test/core_main.cpp
+++ b/clang/tools/c-index-test/core_main.cpp
@@ -223,6 +223,7 @@ static bool printSourceSymbols(const char *Executable,
     Diags(CompilerInstance::createDiagnostics(new DiagnosticOptions));
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
+  CIOpts.ProbePrecompiled = true; // FIXME: historical default. Needed?
   auto CInvok = createInvocation(ArgsWithProgName, std::move(CIOpts));
   if (!CInvok)
     return true;
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index 0534ccac290d..206dd4882886 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -510,6 +510,7 @@ static CXErrorCode clang_indexSourceFile_Impl(
 
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
+  CIOpts.ProbePrecompiled = true; // FIXME: historical default. Needed?
   std::shared_ptr<CompilerInvocation> CInvok =
       createInvocation(*Args, std::move(CIOpts));
 
diff --git a/clang/unittests/Frontend/UtilsTest.cpp b/clang/unittests/Frontend/UtilsTest.cpp
index 4c4b7b969107..ae014d3f86b5 100644
--- a/clang/unittests/Frontend/UtilsTest.cpp
+++ b/clang/unittests/Frontend/UtilsTest.cpp
@@ -48,20 +48,20 @@ TEST(BuildCompilerInvocationTest, ProbePrecompiled) {
   llvm::IntrusiveRefCntPtr<DiagnosticsEngine> CommandLineDiagsEngine =
       clang::CompilerInstance::createDiagnostics(new DiagnosticOptions, &D,
                                                  false);
-  // Default: ProbePrecompiled is true.
+  // Default: ProbePrecompiled=false
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = CommandLineDiagsEngine;
   CIOpts.VFS = FS;
   std::unique_ptr<CompilerInvocation> CI = createInvocation(Args, CIOpts);
   ASSERT_TRUE(CI);
-  EXPECT_THAT(CI->getPreprocessorOpts().Includes, ElementsAre());
-  EXPECT_EQ(CI->getPreprocessorOpts().ImplicitPCHInclude, "foo.h.pch");
-
-  CIOpts.ProbePrecompiled = false;
-  CI = createInvocation(Args, CIOpts);
-  ASSERT_TRUE(CI);
   EXPECT_THAT(CI->getPreprocessorOpts().Includes, ElementsAre("foo.h"));
   EXPECT_EQ(CI->getPreprocessorOpts().ImplicitPCHInclude, "");
+
+  CIOpts.ProbePrecompiled = true;
+  CI = createInvocation(Args, CIOpts);
+  ASSERT_TRUE(CI);
+  EXPECT_THAT(CI->getPreprocessorOpts().Includes, ElementsAre());
+  EXPECT_EQ(CI->getPreprocessorOpts().ImplicitPCHInclude, "foo.h.pch");
 }
 
 } // namespace