<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/78850>78850</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
C++20 Modules: Clang gives error `error: 'std::align' has different definitions in different modules` when just including standard headers in two module partitions
</td>
</tr>
<tr>
<th>Labels</th>
<td>
clang
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
ashley-hawkins
</td>
</tr>
</table>
<pre>
I'm still not sure whether this is a problem with libstdc++ or a problem with clang so I apologise if this is the wrong place to report, but I get this error when including just <chrono> in one module partition and <memory> in another, here is an example on Compiler Explorer: https://godbolt.org/z/Wvv1h5aYa
<details>
<summary>module.cc</summary>
```cpp
module;
#include <chrono>
export module repro;
export import :part;
```
</details>
<details>
<summary>part.cc</summary>
```cpp
module;
#include <memory>
export module repro:part;
```
</details>
In this example I am getting the error `'std::align' has different definitions in different modules`
<details>
<summary>full compiler output</summary>
```
In module 'repro:part' imported from /app/module.cc:4:
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/14.0.1/../../../../include/c++/14.0.1/bits/align.h:61:1: error: 'std::align' has different definitions in different modules; definition in module 'repro:part.<global>' first difference is function body
60 | inline void*
| ~~~~~~~~~~~~
61 | align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
62 | {
| ~
63 | if (__space < __size)
| ~~~~~~~~~~~~~~~~~~~~~
64 | return nullptr;
| ~~~~~~~~~~~~~~~
65 | const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
66 | const auto __aligned = (__intptr - 1u + __align) & -__align;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
67 | const auto __diff = __aligned - __intptr;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
68 | if (__diff > (__space - __size))
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
69 | return nullptr;
| ~~~~~~~~~~~~~~~
70 | else
| ~~~~
71 | {
| ~
72 | __space -= __diff;
| ~~~~~~~~~~~~~~~~~~
73 | return __ptr = reinterpret_cast<void*>(__aligned);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74 | }
| ~
75 | }
| ~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/14.0.1/../../../../include/c++/14.0.1/bits/align.h:61:1: note: but in '' found a different body
60 | inline void*
| ~~~~~~~~~~~~
61 | align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
62 | {
| ~
63 | if (__space < __size)
| ~~~~~~~~~~~~~~~~~~~~~
64 | return nullptr;
| ~~~~~~~~~~~~~~~
65 | const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
66 | const auto __aligned = (__intptr - 1u + __align) & -__align;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
67 | const auto __diff = __aligned - __intptr;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
68 | if (__diff > (__space - __size))
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
69 | return nullptr;
| ~~~~~~~~~~~~~~~
70 | else
| ~~~~
71 | {
| ~
72 | __space -= __diff;
| ~~~~~~~~~~~~~~~~~~
73 | return __ptr = reinterpret_cast<void*>(__aligned);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74 | }
| ~
75 | }
| ~
1 error generated.
```
</details>
I looked at the preprocessed source and saw that the problem causing the function definitions to be considered different was one of them was getting `uintptr_t` from the global namespace, the other was getting `uintptr_t` from a `using` in the std namespace.
I could reproduce the same situation without those included headers to demonstrate the problem:
<details>
<summary>module.cc</summary>
```cc
module;
typedef long T;
namespace ns {
using ::T;
}
namespace ns {
inline void fun() {
(void)(T)0;
}
}
export module repro;
export import :part;
```
</details>
<details>
<summary>part.cc</summary>
```cc
module;
typedef long T;
namespace ns {
inline void fun() {
(void)(T)0;
}
}
export module repro:part;
```
</details>
<details>
<summary>CMakeLists.txt</summary>
```cc
cmake_minimum_required(VERSION 3.28)
project(repro)
set(CMAKE_CXX_STANDARD 20)
add_library(repro)
target_sources(repro PUBLIC FILE_SET CXX_MODULES FILES module.cc part.cc)
```
</details>
And here is the above on compiler explorer: https://godbolt.org/z/Ke6eoGnan and the compiler output from that compiler explorer example:
<details>
<summary>full compiler output</summary>
```
In file included from /app/module.cc:12:
part.cc:4:13: error: 'ns::fun' has different definitions in different modules; definition in module 'repro:part.<global>' first difference is function body
4 | inline void fun() {
| ~~~~~~~~~~~~^~~~~~~
5 | (void)(T)0;
| ~~~~~~~~~~~
6 | }
| ~
module.cc:7:13: note: but in '' found a different body
7 | inline void fun() {
| ~~~~~~~~~~~~^~~~~~~
8 | (void)(T)0;
| ~~~~~~~~~~~
9 | }
| ~
1 error generated.
```
</details>
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsWV9z2zYS_zTQy440FKi_D3qQJfHG06S9qdO73pMGIlciGhDgAaDt9KGfvQOA_yzLcdKoM82MPQklLZaL3R8Wu9gFM4afJOKKTG_IdDtglc2VXjGTC_w0zNnDRy7N4KCyT6tbQucFGMuFAKksmEojPORoc9Rgc26AG2BQanUQWMADtzkIfjA2Swm9IfQGlD4fTwWTJzAKboGVSqgTNwj82IqzOcKDVvIEpWApglWgsVTaErqBQ2XhFk5oAztqrbRTSAKXqagyLk_wW2UskHiT5lpJReIdcAlKIhQqqwRCybTllisJTGaOscBC6U81I5PKWecmy1GjN1ACPrKiFAhKwkYVJReoYfdYCqVRk3gNubWlIfGa0ITQ5KSygxJ2pPSJ0OR3QpP_3t-P8yn7HyPRlkRrEm8ytIwLQ-JdSzJVUTCvSNB0lKYk3hCadAM1b3jOovAvLctACa-R-KZmoHFABZ_AEQbx0WHaYKKx1Kp9sR7jhf8g8dpB1olt5m0VJzS5YM5nLXQSr2tfu4qfse-vGOKft7J2uNoPboEVzg2tczjnscETnSw6NzZzrhCvmeAnSegccmYg48cjapQWMjxy6T3QOI_rBoKypq_RZ0E8VkJA2vijqmxZ2S9CtDWqhofQ-ROE6LxefMzgqFUBhCasLAlNep65njgr65VIVGkJTRplhthsDpqc0nRoJCtNrhyL4IdAJDR5XMz2s8lQcFk9Dk-yIjQZT0bRaExoMho9f9TL7SYK8aX_woFb4_R0oI9yEq9nYxKv3f-wOu7LNVYnvunxOJbLII5IvDkJdWDCrQKdw5FrY1t5qQ8tx0qmXowLtwFLAJhFQOYb4FJwiXCveEbouh0F8KN_9P66N8d-rDZtYfjvuLew39eEDbQU98URGul0Bvt9aXXHFEimZCkSugSp8DHF0p7rQaa7P673V0uf0SB7fvPM7M7W2BPAJQ9CF7WqLhS05i0_B9oF9Ca1RACNttISZCWEAyV-rsdLMqa1jFRJY4FVVsF-z6UtrQYSb0EjlxZ1qdHuU2bchq3C8N56T1nU67B8fdavxhVgNrukn_cPzLyCXoNa4SGMK3B5vHWhJTi_GDa_r6jiEy3nXtYTHd3O8Qp26g5baL9FkW7WxZlH1VPu-v417HnXcweDV6ftZlv6N171NHgutGWZRzULCoOXAOg4x62wC7vKz9Hx0pYI0NodoHeQvKDkJds7mXGPr7bZO_pLm6IJTPWWqJf8Wtui02vSw2Vbky9AMq0D0vaFgPRPT4FSWXSf7gTNpUtWPiepSmbAelnuLRE9seQtEb0lordE9JaIvp9ENK5r0RNK1MxiNvr6aheEUh8xA2Z9cVv6uiZFYzADoyqdou-dGPYANm-ZQpMnZZVpquK2vOkXVVbBAf2O4hlqzHrJ54EZ36lRR_d64X83VTaZRV14mkWhLnWThCILJCuwzhEbT_d9nNdFME92KjsSl_5dY7NO4OgpNqmqRBY6ClmVYuBnBYLhtmLe3Aduc1U5XJTBujWFGeTIMtQegQwLF1LcAvXR6yrq63aI0osNFPupxAyPIJQ8wYeW3BoO0jzdo2FlQ_nc8be-ePnF3unBOQShCx-8-3IJXYRdtiR08YHQZfRcePvle-pcXQH31-D7duz-BpA279lHfMeNNSP7-GU9qQartGAfcV9wyYuq2Gv8f8W1C7eL_-x-vrv96UeIRx6CwF1q9RumltBFMKahh6dBN7J5v_5ht9_8-uv-7sP6x-365y3Q6IyTZdle8IN2Cp7Lskyf0O5D4DPNMPz7l5t3txtIbt_t9ne7D-AmeP_T9pd3uztPvIN2k0LjNO2kXx6M1zJrO9EuUrCDuveN6Lbxh1_RiP4BZ6j-JVlofjt5Z_3DJq4y-3yCpv35xVHq2xuURy56AfTlXuSYtkq1G9Q3KMfxeQNQmhDA_Gb6B3b_YHJedL0UNi_UX00N1DFNu2PFy5HixUNeUwa9cujoL8W8Rf0v1Zwwv6r54ST9DaYDwPLvOXINslWcLeMlG-BqPI-m81kc0fEgX01TGo-XeIzm4zSNcBkds0PG0gU7TKMJMjbgKxrRSTSm0XgaxZPxaDmZRVHEZtFksUyX8YJMIiwYFyMh7gu3_QfcmApX88ViGg0EO6Aw_v6PUn8fRygl0-1Arxz_8FCdDJlEwsfvVoLlVuBqE7oONIL3zY5Yw8bf6Z34PZruJuSqTfdZFK75_OVed9dnLJMZ093Ryp3fHtSzqz4zqLRYnQVHbvPqMEpVQWjirKw_hm1OSTxohtDE4_ZnAAAA__8f3hxk">