[clang][Serialization] Stop including Frontend headers from Serialization (NFC)

[slackito]

The Frontend library depends on Serialization. This is an explicit dependency encoded in the CMake target. However, Serialization currently has an implicit dependency on Frontend, as it includes one of its headers. This is not reflected in the CMake build rules, but Bazel is stricter so, in order to avoid a dependency cycle, it hackily declares the Frontend headers as source files for Serialization.

Fortunately, the only Frontend header used by Serialization is clang/Frontend/FrontendDiagnostic.h, which is a legacy header that just includes clang/Basic/DiagnosticFrontend since d076608, back in 2018.

This commit changes Serialization to use the underlying header from Basic instead. Both Serialization and Frontend depend on Basic, so this breaks the dependency cycle.

[llvmbot]

@llvm/pr-subscribers-clang-modules

@llvm/pr-subscribers-clang

Author: Jorge Gorbe Moya (slackito)

Changes

The Frontend library depends on Serialization. This is an explicit dependency encoded in the CMake target. However, Serialization currently has an implicit dependency on Frontend, as it includes one of its headers. This is not reflected in the CMake build rules, but Bazel is stricter so, in order to avoid a dependency cycle, it hackily declares the Frontend headers as source files for Serialization.

Fortunately, the only Frontend header used by Serialization is clang/Frontend/FrontendDiagnostic.h, which is a legacy header that just includes clang/Basic/DiagnosticFrontend since d076608, back in 2018.

This commit changes Serialization to use the underlying header from Basic instead. Both Serialization and Frontend depend on Basic, so this breaks the dependency cycle.

---

Full diff: https://github.com/llvm/llvm-project/pull/123140.diff

2 Files Affected:

• (modified) clang/lib/Serialization/GeneratePCH.cpp (+1-1)
• (modified) utils/bazel/llvm-project-overlay/clang/BUILD.bazel (-5)

diff --git a/clang/lib/Serialization/GeneratePCH.cpp b/clang/lib/Serialization/GeneratePCH.cpp
index a3189bb40b1912..12751beb8d7157 100644
--- a/clang/lib/Serialization/GeneratePCH.cpp
+++ b/clang/lib/Serialization/GeneratePCH.cpp
@@ -12,7 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/AST/ASTContext.h"
-#include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Basic/DiagnosticFrontend.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/HeaderSearchOptions.h"
 #include "clang/Lex/Preprocessor.h"
diff --git a/utils/bazel/llvm-project-overlay/clang/BUILD.bazel b/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
index a86c295b04cb10..97445d99dc3784 100644
--- a/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
@@ -2148,7 +2148,6 @@ cc_library(
         "include/clang/Serialization/AttrPCHRead.inc",
         "include/clang/Serialization/AttrPCHWrite.inc",
     ] + glob([
-        "include/clang/Frontend/*.h",
         "lib/Serialization/*.cpp",
         "lib/Serialization/*.h",
     ]),
@@ -2160,15 +2159,11 @@ cc_library(
         "include/clang/Serialization/*.def",
     ]),
     deps = [
-        ":apinotes",
         ":ast",
         ":basic",
-        ":driver",
         ":lex",
         ":sema",
         ":serialization_attr_gen",
-        ":static_analyzer_core_options",
-        ":support",
         ":type_nodes_gen",
         "//llvm:BitReader",
         "//llvm:BitWriter",