https://github.com/vvuksanovic updated 
https://github.com/llvm/llvm-project/pull/142149

>From b8481a36b33e71248170c8cc195b45fa9de4f777 Mon Sep 17 00:00:00 2001
From: Vladimir Vuksanovic <vladimir.vuksano...@htecgroup.com>
Date: Fri, 30 May 2025 05:42:55 -0700
Subject: [PATCH 1/3] [clang-reorder-fields] Prevent rewriting unsupported
 cases

Add checks to prevent rewriting when doing so might result in incorrect
code. The following cases are checked:
- There are multiple field declarations in one statement like `int a, b`
- Multiple fields are created from a single macro expansion
- Preprocessor directives are present in the struct
---
 .../ReorderFieldsAction.cpp                   | 60 +++++++++++++++++++
 .../MacroExpandsToMultipleFields.cpp          | 13 ++++
 .../MultipleFieldDeclsInStatement.cpp         | 11 ++++
 .../PreprocessorDirectiveAroundDefinition.cpp | 15 +++++
 .../PreprocessorDirectiveAroundFields.cpp     | 15 +++++
 .../PreprocessorDirectiveInDefinition.cpp     | 16 +++++
 6 files changed, 130 insertions(+)
 create mode 100644 
clang-tools-extra/test/clang-reorder-fields/MacroExpandsToMultipleFields.cpp
 create mode 100644 
clang-tools-extra/test/clang-reorder-fields/MultipleFieldDeclsInStatement.cpp
 create mode 100644 
clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundDefinition.cpp
 create mode 100644 
clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
 create mode 100644 
clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveInDefinition.cpp

diff --git a/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp 
b/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
index ea0207619fb2b..25ee1ec815a9f 100644
--- a/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
+++ b/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
@@ -19,6 +19,7 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Basic/SourceLocation.h"
 #include "clang/Lex/Lexer.h"
 #include "clang/Tooling/Refactoring.h"
 #include "llvm/ADT/STLExtras.h"
@@ -50,6 +51,63 @@ static const RecordDecl *findDefinition(StringRef RecordName,
   return selectFirst<RecordDecl>("recordDecl", Results);
 }
 
+static bool isSafeToRewrite(const RecordDecl *Decl, const ASTContext &Context) 
{
+  // All following checks expect at least one field declaration.
+  if (Decl->field_empty())
+    return true;
+
+  // Don't attempt to rewrite if there is a declaration like 'int a, b;'.
+  SourceLocation LastTypeLoc;
+  for (const auto &Field : Decl->fields()) {
+    SourceLocation TypeLoc =
+        Field->getTypeSourceInfo()->getTypeLoc().getBeginLoc();
+    if (LastTypeLoc.isValid() && TypeLoc == LastTypeLoc)
+      return false;
+    LastTypeLoc = TypeLoc;
+  }
+
+  // Don't attempt to rewrite if a single macro expansion creates multiple
+  // fields.
+  SourceLocation LastMacroLoc;
+  for (const auto &Field : Decl->fields()) {
+    if (!Field->getLocation().isMacroID())
+      continue;
+    SourceLocation MacroLoc =
+        Context.getSourceManager().getExpansionLoc(Field->getLocation());
+    if (LastMacroLoc.isValid() && MacroLoc == LastMacroLoc)
+      return false;
+    LastMacroLoc = MacroLoc;
+  }
+
+  // Prevent rewriting if there are preprocessor directives present between the
+  // start of the first field and the end of last field.
+  const SourceManager &SM = Context.getSourceManager();
+  std::pair<FileID, unsigned> FileAndOffset =
+  SM.getDecomposedLoc(Decl->field_begin()->getBeginLoc());
+  auto LastField = Decl->field_begin();
+  while (std::next(LastField) != Decl->field_end())
+    ++LastField;
+  unsigned EndOffset = SM.getFileOffset(LastField->getEndLoc());
+  StringRef SrcBuffer = SM.getBufferData(FileAndOffset.first);
+  Lexer L(SM.getLocForStartOfFile(FileAndOffset.first), Context.getLangOpts(),
+          SrcBuffer.data(), SrcBuffer.data() + FileAndOffset.second,
+          SrcBuffer.data() + SrcBuffer.size());
+  IdentifierTable Identifiers(Context.getLangOpts());
+  clang::Token T;
+  while (!L.LexFromRawLexer(T) && L.getCurrentBufferOffset() < EndOffset) {
+    if (T.getKind() == tok::hash) {
+      L.LexFromRawLexer(T);
+      if (T.getKind() == tok::raw_identifier) {
+        clang::IdentifierInfo &II = Identifiers.get(T.getRawIdentifier());
+        if (II.getPPKeywordID() != clang::tok::pp_not_keyword)
+          return false;
+      }
+    }
+  }
+
+  return true;
+}
+
 /// Calculates the new order of fields.
 ///
 /// \returns empty vector if the list of fields doesn't match the definition.
@@ -341,6 +399,8 @@ class ReorderingConsumer : public ASTConsumer {
     const RecordDecl *RD = findDefinition(RecordName, Context);
     if (!RD)
       return;
+    if (!isSafeToRewrite(RD, Context))
+      return;
     SmallVector<unsigned, 4> NewFieldsOrder =
         getNewFieldsOrder(RD, DesiredFieldsOrder);
     if (NewFieldsOrder.empty())
diff --git 
a/clang-tools-extra/test/clang-reorder-fields/MacroExpandsToMultipleFields.cpp 
b/clang-tools-extra/test/clang-reorder-fields/MacroExpandsToMultipleFields.cpp
new file mode 100644
index 0000000000000..5bafcd19ea829
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-reorder-fields/MacroExpandsToMultipleFields.cpp
@@ -0,0 +1,13 @@
+// RUN: clang-reorder-fields -record-name ::bar::Foo -fields-order z,y,x %s -- 
| FileCheck %s
+
+namespace bar {
+
+#define FIELDS_DECL int x; int y; // CHECK: {{^#define FIELDS_DECL int x; int 
y;}}
+
+// The order of fields should not change.
+struct Foo {
+  FIELDS_DECL  // CHECK:      {{^ FIELDS_DECL}}
+  int z;       // CHECK-NEXT: {{^ int z;}}
+};
+
+} // end namespace bar
diff --git 
a/clang-tools-extra/test/clang-reorder-fields/MultipleFieldDeclsInStatement.cpp 
b/clang-tools-extra/test/clang-reorder-fields/MultipleFieldDeclsInStatement.cpp
new file mode 100644
index 0000000000000..437e7b91e27a3
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-reorder-fields/MultipleFieldDeclsInStatement.cpp
@@ -0,0 +1,11 @@
+// RUN: clang-reorder-fields -record-name ::bar::Foo -fields-order z,y,x %s -- 
| FileCheck %s
+
+namespace bar {
+
+// The order of fields should not change.
+struct Foo {
+  int x, y; // CHECK: {{^  int x, y;}}
+  double z; // CHECK-NEXT: {{^  double z;}}
+};
+
+} // end namespace bar
diff --git 
a/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundDefinition.cpp
 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundDefinition.cpp
new file mode 100644
index 0000000000000..f00b4b0b57bf7
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundDefinition.cpp
@@ -0,0 +1,15 @@
+// RUN: clang-reorder-fields -record-name ::bar::Foo -fields-order y,x %s -- | 
FileCheck %s
+
+namespace bar {
+
+#define DEFINE_FOO
+
+// This is okay to reorder.
+#ifdef DEFINE_FOO
+struct Foo {
+  int x;     // CHECK:      {{^ int y;}}
+  int y;     // CHECK-NEXT: {{^ int x;}}
+};
+#endif
+
+} // end namespace bar
diff --git 
a/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
new file mode 100644
index 0000000000000..0c22f19985a8e
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
@@ -0,0 +1,15 @@
+// RUN: clang-reorder-fields -record-name ::bar::Foo -fields-order y,x %s -- | 
FileCheck %s
+
+namespace bar {
+
+#define DEFINE_FIELDS
+
+// This is okay to reorder.
+struct Foo {
+#ifdef DEFINE_FIELDS // CHECK:      {{^#ifdef DEFINE_FIELDS}}
+  int y;             // CHECK-NEXT: {{^ int y;}}
+  int x;             // CHECK-NEXT: {{^ int x;}}
+#endif               // CHECK-NEXT: {{^#endif}}
+};
+
+} // end namespace bar
diff --git 
a/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveInDefinition.cpp
 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveInDefinition.cpp
new file mode 100644
index 0000000000000..fee6b0e637b9b
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveInDefinition.cpp
@@ -0,0 +1,16 @@
+// RUN: clang-reorder-fields -record-name ::bar::Foo -fields-order z,y,x %s -- 
| FileCheck %s
+
+namespace bar {
+
+#define ADD_Z
+
+// The order of fields should not change.
+struct Foo {
+  int x;     // CHECK:      {{^ int x;}}
+  int y;     // CHECK-NEXT: {{^ int y;}}
+#ifdef ADD_Z // CHECK-NEXT: {{^#ifdef ADD_Z}}
+  int z;     // CHECK-NEXT: {{^ int z;}}
+#endif       // CHECK-NEXT: {{^#endif}}
+};
+
+} // end namespace bar

>From e7bff07c40b5525199e5e288a55c55e2a875776c Mon Sep 17 00:00:00 2001
From: Vladimir Vuksanovic <vladimir.vuksano...@htecgroup.com>
Date: Mon, 16 Jun 2025 03:54:11 -0700
Subject: [PATCH 2/3] fixup! [clang-reorder-fields] Prevent rewriting
 unsupported cases

---
 .../PreprocessorDirectiveAroundFields.cpp                     | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git 
a/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
index 0c22f19985a8e..c37546a05afd3 100644
--- 
a/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
+++ 
b/clang-tools-extra/test/clang-reorder-fields/PreprocessorDirectiveAroundFields.cpp
@@ -7,8 +7,8 @@ namespace bar {
 // This is okay to reorder.
 struct Foo {
 #ifdef DEFINE_FIELDS // CHECK:      {{^#ifdef DEFINE_FIELDS}}
-  int y;             // CHECK-NEXT: {{^ int y;}}
-  int x;             // CHECK-NEXT: {{^ int x;}}
+  int x;             // CHECK-NEXT: {{^ int y;}}
+  int y;             // CHECK-NEXT: {{^ int x;}}
 #endif               // CHECK-NEXT: {{^#endif}}
 };
 

>From 6873c7f8d08b7d9222fee5d520888b68741c7de9 Mon Sep 17 00:00:00 2001
From: Vladimir Vuksanovic <vladimir.vuksano...@htecgroup.com>
Date: Mon, 16 Jun 2025 07:22:26 -0700
Subject: [PATCH 3/3] fixup! [clang-reorder-fields] Prevent rewriting
 unsupported cases

---
 clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp 
b/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
index 25ee1ec815a9f..d9c55fd9c0cac 100644
--- a/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
+++ b/clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
@@ -83,7 +83,7 @@ static bool isSafeToRewrite(const RecordDecl *Decl, const 
ASTContext &Context) {
   // start of the first field and the end of last field.
   const SourceManager &SM = Context.getSourceManager();
   std::pair<FileID, unsigned> FileAndOffset =
-  SM.getDecomposedLoc(Decl->field_begin()->getBeginLoc());
+      SM.getDecomposedLoc(Decl->field_begin()->getBeginLoc());
   auto LastField = Decl->field_begin();
   while (std::next(LastField) != Decl->field_end())
     ++LastField;

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