[clang][Modules] Import then include fails to merge inline lambdas

[davidstone]

Given the following valid translation units:

module;

inline auto x = []{};

export module a;

module;

import a;

inline auto x = []{};

export module b;

clang erroneously rejects with

b.cpp:5:13: error: redeclaration of 'x' with a different type: '(lambda at /app/b.cpp:5:17)' vs '(lambda at /app/a.cpp:3:17)'
    5 | inline auto x = []{};
      |             ^
a.cpp:3:13: note: previous definition is here
    3 | inline auto x = []{};
      |             ^
1 error generated.

See it live: https://godbolt.org/z/WxW47zW4v

This is the reduced version of the following reproducer:

module;

#include <compare>

export module a;

module;

import a;
#include <compare>

export module b;

in which clang with libc++ erroneously rejects with

In file included from /app/b.cpp:4:
In file included from /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/compare:156:
/opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: error: redeclaration of '__synth_three_way' with a different type: 'const std::__1::(lambda at /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:65)' vs 'const std::__1::(lambda at /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:65)'
   28 | _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way = []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
      |                                             ^
/opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: note: previous definition is here
   28 | _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way = []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
      |                                             ^
1 error generated.

See it live: https://godbolt.org/z/4dK717sr4

Looks like the library side of it was reintroduced by d043e4c @H-G-Hristov, @Zingam but I suspect that the clang side of it was never fully fixed. #57222 @ChuanqiXu9 shows a unit test for two modules that just include a header with an inline lambda, but this case of import module that included, followed by include appears to have slipped through.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: David Stone (davidstone)

Given the following valid translation units:

module;

inline auto x = []{};

export module a;

module;

import a;

inline auto x = []{};

export module b;

clang erroneously rejects with

b.cpp:5:13: error: redeclaration of 'x' with a different type: '(lambda at /app/b.cpp:5:17)' vs '(lambda at /app/a.cpp:3:17)'
    5 | inline auto x = []{};
      |             ^
a.cpp:3:13: note: previous definition is here
    3 | inline auto x = []{};
      |             ^
1 error generated.

See it live: https://godbolt.org/z/WxW47zW4v

This is the reduced version of the following reproducer:

module;

#include <compare>

export module a;

module;

import a;
#include <compare>

export module b;

in which clang with libc++ erroneously rejects with

In file included from /app/b.cpp:4:
In file included from /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/compare:156:
/opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: error: redeclaration of '__synth_three_way' with a different type: 'const std::__1::(lambda at /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:65)' vs 'const std::__1::(lambda at /opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:65)'
   28 | _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way = []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
      |                                             ^
/opt/compiler-explorer/clang-assertions-trunk-20240809/bin/../include/c++/v1/__compare/synth_three_way.h:28:45: note: previous definition is here
   28 | _LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way = []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
      |                                             ^
1 error generated.

See it live: https://godbolt.org/z/4dK717sr4

Looks like the library side of it was reintroduced by d043e4c @H-G-Hristov, @Zingam but I suspect that the clang side of it was never fully fixed. #57222 @ChuanqiXu9 shows a unit test for two modules that just include a header with an inline lambda, but this case of import module that included, followed by include appears to have slipped through.