`test_body` fails with C++20 P1766R1, `non-c-typedef-for-linkage`

[cuviper]

Since Clang 11 (commit 7ae1b4a0ce9c) and soon in GCC 16 (commit 828c48f0680e), test_body fails on non-c-typedef-for-linkage.

With clang-21.1.8-6.fc44.x86_64:

Running: "/root/cbindgen/target/debug/cbindgen" "--output" "/root/cbindgen/tests/expectations/body.compat.c" "--depfile" "/tmp/.tmpJyyVas" "--lang" "c" "--cpp-compat" "--style" "type" "--config" "/root/cbindgen/tests/rust/body.toml" "/root/cbindgen/tests/rust/body.rs"
Running: "clang" "-D" "DEFINED" "-I" "/root/cbindgen/tests" "-Wall" "-Werror" "-Wno-attributes" "-Wno-unused-const-variable" "-Wno-return-type-c-linkage" "-Wno-deprecated-declarations" "-D" "CBINDGEN_STYLE_TYPE" "-D" "CBINDGEN_CPP_COMPAT" "-o" "/tmp/cbindgen-test-outputIdxH5u/body.compat.o" "-c" "/root/cbindgen/tests/expectations/body.compat.c"
Running: "clang++" "-D" "DEFINED" "-I" "/root/cbindgen/tests" "-Wall" "-Werror" "-Wno-attributes" "-Wno-unused-const-variable" "-Wno-return-type-c-linkage" "-Wno-deprecated-declarations" "-std=c++17" "-x" "c++" "-D" "CBINDGEN_STYLE_TYPE" "-D" "CBINDGEN_CPP_COMPAT" "-o" "/tmp/cbindgen-test-outputIdxH5u/body.compat.o" "-c" "/root/cbindgen/tests/expectations/body.compat.c"

thread 'test_body' (37465) panicked at tests/tests.rs:214:5:
Output failed to compile: Output { status: ExitStatus(unix_wait_status(256)), stdout: "", stderr: "/root/cbindgen/tests/expectations/body.compat.c:18:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]\n   18 | typedef struct {\n      |               ^\n      |                MyFancyStruct\n/root/cbindgen/tests/expectations/body.compat.c:21:5: note: type is not C-compatible due to this member declaration\n   21 |     inline void foo();\n      |     ^~~~~~~~~~~~~~~~~\n/root/cbindgen/tests/expectations/body.compat.c:23:3: note: type is given name 'MyFancyStruct' for linkage purposes by this typedef declaration\n   23 | } MyFancyStruct;\n      |   ^\n/root/cbindgen/tests/expectations/body.compat.c:31:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]\n   31 | typedef struct {\n      |               ^\n      |                MyFancyEnum\n/root/cbindgen/tests/expectations/body.compat.c:42:5: note: type is not C-compatible due to this member declaration\n   42 |     inline void wohoo();\n      |     ^~~~~~~~~~~~~~~~~~~\n/root/cbindgen/tests/expectations/body.compat.c:44:3: note: type is given name 'MyFancyEnum' for linkage purposes by this typedef declaration\n   44 | } MyFancyEnum;\n      |   ^\n/root/cbindgen/tests/expectations/body.compat.c:52:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]\n   52 | typedef struct {\n      |               ^\n      |                MyFancyStruct_Prepended\n/root/cbindgen/tests/expectations/body.compat.c:54:5: note: type is not C-compatible due to this member declaration\n   54 |     inline void prepended_wohoo();\n      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n/root/cbindgen/tests/expectations/body.compat.c:57:3: note: type is given name 'MyFancyStruct_Prepended' for linkage purposes by this typedef declaration\n   57 | } MyFancyStruct_Prepended;\n      |   ^\n/root/cbindgen/tests/expectations/body.compat.c:65:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]\n   65 | typedef struct {\n      |               ^\n      |                MyFancyEnum_Prepended\n/root/cbindgen/tests/expectations/body.compat.c:67:5: note: type is not C-compatible due to this member declaration\n   67 |     inline void wohoo();\n      |     ^~~~~~~~~~~~~~~~~~~\n/root/cbindgen/tests/expectations/body.compat.c:78:3: note: type is given name 'MyFancyEnum_Prepended' for linkage purposes by this typedef declaration\n   78 | } MyFancyEnum_Prepended;\n      |   ^\n4 errors generated.\n" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

newline-expanded clang stderr:

/root/cbindgen/tests/expectations/body.compat.c:18:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
   18 | typedef struct {
      |               ^
      |                MyFancyStruct
/root/cbindgen/tests/expectations/body.compat.c:21:5: note: type is not C-compatible due to this member declaration
   21 |     inline void foo();
      |     ^~~~~~~~~~~~~~~~~
/root/cbindgen/tests/expectations/body.compat.c:23:3: note: type is given name 'MyFancyStruct' for linkage purposes by this typedef declaration
   23 | } MyFancyStruct;
      |   ^
/root/cbindgen/tests/expectations/body.compat.c:31:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
   31 | typedef struct {
      |               ^
      |                MyFancyEnum
/root/cbindgen/tests/expectations/body.compat.c:42:5: note: type is not C-compatible due to this member declaration
   42 |     inline void wohoo();
      |     ^~~~~~~~~~~~~~~~~~~
/root/cbindgen/tests/expectations/body.compat.c:44:3: note: type is given name 'MyFancyEnum' for linkage purposes by this typedef declaration
   44 | } MyFancyEnum;
      |   ^
/root/cbindgen/tests/expectations/body.compat.c:52:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
   52 | typedef struct {
      |               ^
      |                MyFancyStruct_Prepended
/root/cbindgen/tests/expectations/body.compat.c:54:5: note: type is not C-compatible due to this member declaration
   54 |     inline void prepended_wohoo();
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/root/cbindgen/tests/expectations/body.compat.c:57:3: note: type is given name 'MyFancyStruct_Prepended' for linkage purposes by this typedef declaration
   57 | } MyFancyStruct_Prepended;
      |   ^
/root/cbindgen/tests/expectations/body.compat.c:65:15: error: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage]
   65 | typedef struct {
      |               ^
      |                MyFancyEnum_Prepended
/root/cbindgen/tests/expectations/body.compat.c:67:5: note: type is not C-compatible due to this member declaration
   67 |     inline void wohoo();
      |     ^~~~~~~~~~~~~~~~~~~
/root/cbindgen/tests/expectations/body.compat.c:78:3: note: type is given name 'MyFancyEnum_Prepended' for linkage purposes by this typedef declaration
   78 | } MyFancyEnum_Prepended;
      |   ^
4 errors generated.

With gcc-16.0.1-0.5.fc44.x86_64:

Running: "/root/cbindgen/target/debug/cbindgen" "--output" "/root/cbindgen/tests/expectations/body.compat.c" "--depfile" "/tmp/.tmp4IgFnp" "--lang" "c" "--cpp-compat" "--style" "type" "--config" "/root/cbindgen/tests/rust/body.toml" "/root/cbindgen/tests/rust/body.rs"
Running: "gcc" "-D" "DEFINED" "-I" "/root/cbindgen/tests" "-Wall" "-Werror" "-Wno-attributes" "-Wno-unused-const-variable" "-Wno-return-type-c-linkage" "-Wno-deprecated-declarations" "-D" "CBINDGEN_STYLE_TYPE" "-D" "CBINDGEN_CPP_COMPAT" "-o" "/tmp/cbindgen-test-outputHh99aD/body.compat.o" "-c" "/root/cbindgen/tests/expectations/body.compat.c"
Running: "g++" "-D" "DEFINED" "-I" "/root/cbindgen/tests" "-Wall" "-Werror" "-Wno-attributes" "-Wno-unused-const-variable" "-Wno-return-type-c-linkage" "-Wno-deprecated-declarations" "-std=c++17" "-x" "c++" "-D" "CBINDGEN_STYLE_TYPE" "-D" "CBINDGEN_CPP_COMPAT" "-o" "/tmp/cbindgen-test-outputHh99aD/body.compat.o" "-c" "/root/cbindgen/tests/expectations/body.compat.c"

thread 'test_body' (37474) panicked at tests/tests.rs:214:5:
Output failed to compile: Output { status: ExitStatus(unix_wait_status(256)), stdout: "", stderr: "/root/cbindgen/tests/expectations/body.compat.c:18:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]\n   18 | typedef struct {\n      |                ^\n      |                MyFancyStruct\n/root/cbindgen/tests/expectations/body.compat.c:21:17: note: type is not C-compatible because it contains ‘void MyFancyStruct::foo()’ declaration\n   21 |     inline void foo();\n      |                 ^~~\n/root/cbindgen/tests/expectations/body.compat.c:31:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]\n   31 | typedef struct {\n      |                ^\n      |                MyFancyEnum\n/root/cbindgen/tests/expectations/body.compat.c:42:17: note: type is not C-compatible because it contains ‘void MyFancyEnum::wohoo()’ declaration\n   42 |     inline void wohoo();\n      |                 ^~~~~\n/root/cbindgen/tests/expectations/body.compat.c:52:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]\n   52 | typedef struct {\n      |                ^\n      |                MyFancyStruct_Prepended\n/root/cbindgen/tests/expectations/body.compat.c:54:17: note: type is not C-compatible because it contains ‘void MyFancyStruct_Prepended::prepended_wohoo()’ declaration\n   54 |     inline void prepended_wohoo();\n      |                 ^~~~~~~~~~~~~~~\n/root/cbindgen/tests/expectations/body.compat.c:65:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]\n   65 | typedef struct {\n      |                ^\n      |                MyFancyEnum_Prepended\n/root/cbindgen/tests/expectations/body.compat.c:67:17: note: type is not C-compatible because it contains ‘void MyFancyEnum_Prepended::wohoo()’ declaration\n   67 |     inline void wohoo();\n      |                 ^~~~~\ncc1plus: note: unrecognized command-line option ‘-Wno-return-type-c-linkage’ may have been intended to silence earlier diagnostics\ncc1plus: all warnings being treated as errors\n" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

newline-expanded gcc stderr:

/root/cbindgen/tests/expectations/body.compat.c:18:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]
   18 | typedef struct {
      |                ^
      |                MyFancyStruct
/root/cbindgen/tests/expectations/body.compat.c:21:17: note: type is not C-compatible because it contains ‘void MyFancyStruct::foo()’ declaration
   21 |     inline void foo();
      |                 ^~~
/root/cbindgen/tests/expectations/body.compat.c:31:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]
   31 | typedef struct {
      |                ^
      |                MyFancyEnum
/root/cbindgen/tests/expectations/body.compat.c:42:17: note: type is not C-compatible because it contains ‘void MyFancyEnum::wohoo()’ declaration
   42 |     inline void wohoo();
      |                 ^~~~~
/root/cbindgen/tests/expectations/body.compat.c:52:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]
   52 | typedef struct {
      |                ^
      |                MyFancyStruct_Prepended
/root/cbindgen/tests/expectations/body.compat.c:54:17: note: type is not C-compatible because it contains ‘void MyFancyStruct_Prepended::prepended_wohoo()’ declaration
   54 |     inline void prepended_wohoo();
      |                 ^~~~~~~~~~~~~~~
/root/cbindgen/tests/expectations/body.compat.c:65:16: error: anonymous non-C-compatible type given name for linkage purposes by ‘typedef’ declaration [-Werror=non-c-typedef-for-linkage]
   65 | typedef struct {
      |                ^
      |                MyFancyEnum_Prepended
/root/cbindgen/tests/expectations/body.compat.c:67:17: note: type is not C-compatible because it contains ‘void MyFancyEnum_Prepended::wohoo()’ declaration
   67 |     inline void wohoo();
      |                 ^~~~~
cc1plus: note: unrecognized command-line option ‘-Wno-return-type-c-linkage’ may have been intended to silence earlier diagnostics
cc1plus: all warnings being treated as errors

[cuviper]

Since Clang 11 (commit 7ae1b4a0ce9c)

I misunderstood that change as the start, but Clang had an error long before that, since commit 2575d8805927.

I haven't actually tried any of these older versions with cbindgen anyway.

[cuviper]

I suppose the cheap fix is to add -Wno-non-c-typedef-for-linkage to the tests::compile command.

However, I wonder if it's possible for cbindgen to detect that the tag is needed here. It doesn't help that the "fancy" parts of these types that run afoul of P1766R1 are only added in raw [export.body] or [export.pre_body] strings.