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[clang-reorder-fields] Check for flexible array member #160262

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Merged
merged 1 commit into from
Sep 29, 2025
Merged

[clang-reorder-fields] Check for flexible array member #160262

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20 changes: 18 additions & 2 deletions clang-tools-extra/clang-reorder-fields/ReorderFieldsAction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,22 @@ getNewFieldsOrder(const RecordDecl *Definition,
return NewFieldsOrder;
}

static bool isOrderValid(const RecordDecl *RD, ArrayRef<unsigned> FieldOrder) {
if (FieldOrder.empty())
return false;

// If there is a flexible array member in the struct, it must remain the last
// field.
if (RD->hasFlexibleArrayMember() &&
FieldOrder.back() != FieldOrder.size() - 1) {
llvm::errs()
<< "Flexible array member must remain the last field in the struct\n";
return false;
}

return true;
}

struct ReorderedStruct {
public:
ReorderedStruct(const RecordDecl *Decl, ArrayRef<unsigned> NewFieldsOrder)
Expand Down Expand Up @@ -662,7 +678,7 @@ class ReorderingConsumer : public ASTConsumer {
return;
SmallVector<unsigned, 4> NewFieldsOrder =
getNewFieldsOrder(RD, DesiredFieldsOrder);
if (NewFieldsOrder.empty())
if (!isOrderValid(RD, NewFieldsOrder))
return;
ReorderedStruct RS{RD, NewFieldsOrder};

Expand Down Expand Up @@ -699,7 +715,7 @@ class ReorderingConsumer : public ASTConsumer {

std::unique_ptr<ASTConsumer> ReorderFieldsAction::newASTConsumer() {
return std::make_unique<ReorderingConsumer>(RecordName, DesiredFieldsOrder,
Replacements);
Replacements);
}

} // namespace reorder_fields
Expand Down
10 changes: 10 additions & 0 deletions clang-tools-extra/test/clang-reorder-fields/FlexibleArrayMember.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
// RUN: clang-reorder-fields -record-name Foo -fields-order z,y,x %s -- 2>&1 | FileCheck --check-prefix=CHECK-BAD %s
// RUN: clang-reorder-fields -record-name Foo -fields-order y,x,z %s -- | FileCheck --check-prefix=CHECK-GOOD %s

// CHECK-BAD: {{^Flexible array member must remain the last field in the struct}}

struct Foo {
int x; // CHECK-GOOD: {{^ int y;}}
int y; // CHECK-GOOD-NEXT: {{^ int x;}}
int z[]; // CHECK-GOOD-NEXT: {{^ int z\[\];}}
};