[clang-format] Struct/class declaration with export macro treated as initialization in clang-format 19

[rmarker]

In our codebase, we use macros when exporting types for dlls.
This enables conditionally enabling exporting the type, as well as supporting different compilers (e.g. __declspec(dllexport) vs __attribute__ ((dllexport))).

In clang-format 18.1.6 this formats as expected.
E.g. using the default style:

struct EXPORT StructName {};

class EXPORT ClassName {
public:
  ClassName() {}
};

However, testing the latest version of clang-format 19 (f779ec7), the formatting has changed.
It appears that it is instead interpreting it as an initialization.
I.e.

struct EXPORT StructName{};

class EXPORT ClassName{public : ClassName(){}};

[owenca]

In clang-format 19, struct foo bar {}; is correctly annotated as:

AnnotatedTokens(L=0, P=0, T=5, C=0):
 M=0 C=0 T=Unknown S=1 F=0 B=0 BK=0 P=0 Name=struct L=6 PPK=2 FakeLParens= FakeRParens=0 II=0x12a00fd40 Text='struct'
 M=0 C=1 T=Unknown S=1 F=0 B=0 BK=0 P=5020 Name=identifier L=10 PPK=2 FakeLParens= FakeRParens=0 II=0x12a0187b8 Text='foo'
 M=0 C=1 T=StartOfName S=1 F=0 B=0 BK=0 P=220 Name=identifier L=14 PPK=2 FakeLParens= FakeRParens=0 II=0x12a0187e8 Text='bar'
 M=0 C=0 T=Unknown S=0 F=0 B=0 BK=2 P=23 Name=l_brace L=15 PPK=2 FakeLParens= FakeRParens=0 II=0x0 Text='{'
 M=0 C=0 T=Unknown S=0 F=0 B=0 BK=2 P=41 Name=r_brace L=16 PPK=2 FakeLParens= FakeRParens=0 II=0x0 Text='}'
 M=0 C=0 T=Unknown S=0 F=0 B=0 BK=0 P=23 Name=semi L=17 PPK=2 FakeLParens= FakeRParens=0 II=0x0 Text=';'

If foo is a macro instead of the struct/class name, clang-format needs to be told so, e.g. by the AttributeMacros option:

$ cat input.cpp
struct EXPORT StructName {};

class EXPORT ClassName {
public:
  ClassName() {}
};
$ clang-format -style='{AttributeMacros: [EXPORT]}' input.cpp | diff input.cpp -
$ 

[rmarker]

Oh, I don't think I've ever come across something like struct foo bar {}; before. Searching around, it seems to be more commonly used in C rather than C++.

I tried using AttributeMacros but it doesn't seem to be working for me. Strange.

$ cat input.cpp
struct EXPORT StructName {};

class EXPORT ClassName {
public:
  ClassName() {}
};

$ ./build/Debug/bin/clang-format.exe -style='{AttributeMacros: [EXPORT]}' input.cpp | diff input.cpp -
1c1
< struct EXPORT StructName {};
---
> struct EXPORT StructName{};
3,6c3
< class EXPORT ClassName {
< public:
<   ClassName() {}
< };
\ No newline at end of file
---
> class EXPORT ClassName{public : ClassName(){}};
\ No newline at end of file


$ ./build/Debug/bin/clang-format.exe -version
clang-format version 19.0.0git (https://github.com/llvm/llvm-project.git f779ec7c13bdfccd29655d13a325f34c60797a76)

Unless I've made some silly typo somewhere that I cannot spot ;)

[HazardyKnusperkeks]

To chime in: When did it break and why? This is so common code on Windows it should work out of the box, as it did before.

[owenca]

Oh, I don't think I've ever come across something like struct foo bar {}; before. Searching around, it seems to be more commonly used in C rather than C++.

I tried using AttributeMacros but it doesn't seem to be working for me. Strange.

I was using the patch in #94189.

[owenca]

To chime in: When did it break and why? This is so common code on Windows it should work out of the box, as it did before.

See #89706. I'm not sure if it's ok to have the following by default:

struct Foo bar{};
struct FOO bar {};

WDYT @mydeveloperday @rymiel ?

[owenca]

Also, what should be done to struct T bar{};? We can't assume that T is a macro.

[HazardyKnusperkeks]

I'd also be fine with .contains("EXPORT"), that should cover most cases.
Or we get an AttributeMacroRegex.

[rmarker]

At least in our case, we have many different macros for exporting various libraries.
A way of using regex for the attribute macros would be much nicer.

I found #57054, so it seems like that functionality could be useful in other situations as well.