<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/131490>131490</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Problems build partition module using command lines from Clang 21 Standard C++ Modules page
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          rmerriam
      </td>
    </tr>
</table>

<pre>
    I am encountering a problem building a partition module based on these [command lines]( https://clang.llvm.org/docs/StandardCPlusPlusModules.html#id15) on the page **Clang 21 Standard C++ Modules**. The system is Ubuntu 24.04 and Clang 19 and 20. I’m working a talk and book about modules so want to present all the options. 

My actual command lines and the errors are:

```c++
+ clang++ -std=c++23 Balinese.cppm --precompile -o bin/Javanese-Balinese.pcm
+ clang++ -std=c++23 balinesex.cppm --precompile -fprebuilt-module-path=bin -o bin/Javanese-balinese.pcm
+ clang++ -std=c++23 Javanese.cppm --precompile -fprebuilt-module-path=bin -o bin/Javanese.pcm
+ clang++ -std=c++23 javanesex.cppm -fprebuilt-module-path=bin -c -o bin/javanese.o
+ clang++ -std=c++23 bin/Javanese-Balinese.pcm -fprebuilt-module-path=bin -c -o bin/Javanese-Balinese.o
+ clang++ -std=c++23 bin/Javanese-balinese.pcm -fprebuilt-module-path=bin -c -o bin/Javanese-balinese.o
+ clang++ -std=c++23 bin/Javanese.pcm -fprebuilt-module-path=bin -c -o bin/Javanese.o
+ clang++ -std=c++23 main.cpp -fprebuilt-module-path=bin -c -o bin/main.o
+ clang++ bin/main.o bin/Javanese-Balinese.o bin/Javanese-balinese.o bin/Javanese.o bin/javanese.o -o bin/main
/usr/bin/ld: bin/Javanese-balinese.o: in function `initializer for module Javanese:Balinese':
Javanese-balinese.pcm:(.text.startup+0x0): multiple definition of `initializer for module Javanese:Balinese'; bin/Javanese-Balinese.o:Javanese-Balinese.pcm:(.text.startup+0x0): first defined here
/usr/bin/ld: bin/javanese.o: in function `initializer for module Javanese':
javanesex-ab7ff5.pcm:(.text.startup+0x0): multiple definition of `initializer for module Javanese'; bin/Javanese.o:Javanese.pcm:(.text.startup+0x0): first defined here

```

Why is line 2 required since the partition implementation file isn’t an MIU? 

Also, I needed to add `export` to the `module Javanese;` line in `javanesex.cppm` file that isn’t needed in the build shown below. With that added the file compiled but then there were errors:

`````
/usr/bin/ld: bin/Javanese-balinese.o: in function `initializer for module Javanese:Balinese':
Javanese-balinese.pcm:(.text.startup+0x0): multiple definition of `initializer for module Javanese:Balinese'; bin/Javanese-Balinese.o:Javanese-Balinese.pcm:(.text.startup+0x0): first defined here
/usr/bin/ld: bin/javanese.o: in function `initializer for module Javanese':
javanesex-9003c5.pcm:(.text.startup+0x0): multiple definition of `initializer for module Javanese'; bin/Javanese.o:Javanese.pcm:(.text.startup+0x0): first defined here

`````

Why are `balinesex.cppm` and `javanesex.cppm` built as MIU since they are Module Implementation Files?

The translation units build fine with GCC-14 and these command lines with Clang. This is not a problem with the code but the command lines. 

```
+ clang++ -std=c++23 --precompile Balinese.cppm -o bin/Javanese-Balinese.pcm
+ clang++ -std=c++23 --precompile -fprebuilt-module-path=bin Javanese.cppm -o bin/Javanese.pcm

+ clang++ -std=c++23 -c -fprebuilt-module-path=bin Javanese.cppm -o bin/Javanese.o
+ clang++ -std=c++23 -c -fprebuilt-module-path=bin javanese.cpp -o bin/javanese.o
+ clang++ -std=c++23 -c -fprebuilt-module-path=bin balinese.cpp -o bin/balinese.o

+ clang++ -std=c++23 -r bin/Javanese.o bin/javanese.o bin/balinese.o -o bin/Javanese.Module.o

+ clang++ -std=c++23 -c -fprebuilt-module-path=bin main.cpp -o bin/main.o
+ clang++ -std=c++23 bin/Javanese.Module.o bin/main.o -o bin/main

```


</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsWE1v4zYQ_TX0ZWCBomzHOvhgJ3WRAgss0C72TIljixuKVEkqTvrrC1JS4q_E3gQ9tCiQD4iamTd80sw8kTsntxpxQaYrMr0b8dZXxi5sjdZKXo8KI54X98BrQF2aVnu0Um-BQ2NNobCGopVK9Evceuml0VAb0SqEgjsUYDT4Ch0Cma5KU9dcC1BSoyPTO8LmUHnfOJItCVsTti4V19tEqcc6MXZL2FqY0hG2_t1zLbgVt19V68Lvl4jhksrXirBMinRKWN6jQcO3CIQtCVvehojAUhhCwC1hK8JW0IfozBL4o0Jwz85jDdLBt6LVvgU2SegEQs5dnDSPF4wmcE9-YWROSZ7XsDP2oWPBc_UQTQpjHoAXpvU9Hw6cgR3XHryBxqJD7YErFRM2TWDOJUDoktDll2fgpW-5ggPKYuBgjtYa64BbDMxFFzKj3U_ZbS8ssRVEQvsNj50XJLvrDVgGKx7DYlI2TQ3jcWOxNHUjFcLYQCE1Yevf-CMPNuMX46asrwle9PZP56JvGovh3fHjjpxxw31FsrtC6jPQxU9CD46fRr4W8EdvP-z1XZDyFWfwS8xVjL79QK6HPHX_CHbxOeziE9gfg7wOqeZSh0d4ffzocS72_u23qX-bmJP8T16ZwyRiCuvWWcLW3aoSJFu-w3y2BKlh0-oydm0yo1JLL7mSf6GFjbFDIx-cSbYcMifspus852s0tPN54vHJJ85z69uGsBV9ooTlAbZulZeNQhC4iZhGg9l8IIPVOy91tjzfui7ktpHW-S4xFFChxfeZ3Svhnyd0YPGlf4x5cbPZTP9ZEs8xd0DYx3nam0Pd5ffqOYzTwD8wsPhnKy0KcFKX2I_qQTbIulFYo_Y8Xm5Cu5ZOv4xZD1zDl_tvJFv3Y3KpnCHsFu5BIwoUYbJyIQIH-NQY68mMhrWAQ2b05GVahfsxNRkf12EbDzdjEr7i_iiTHk92ciOqIHCV2WkoUJldAt-lrzpHLmJmFXbB-kEkoGh9WI0RLMIu_Onm-ulMf2X0_xL_15d4TmlW_jdK_KjQuY11dqj8QhkF3Xq2vuKIBe5CXb82hS5Sp8_h_rAtrGXQ7Nm6Qw2i3Vuunerutlp619djSBt2oQ5_vb0dp5NBPTs8UtXRJur78BUgXWhY2vi9z5xdV83BUeBQuYdRBul-WK0X9MaBND1S458W4Nfr3iO9_JYKvgaz_BzSVSrtEsiPPZCPau1LGMXew3rFONS118DYK3TecewzvHW1cj3shd296uCLOveSWh8yOxTEJ9L1RDiMxCITeZbzES7Smwmj-TydZaNqwYsym07ms3Q2ucnTCaWTsqTz6UYwRmk6T0dywSib0iyd0QnNWZZM2Q1n02IubhidzcqcTCjWXKqXc4aRdK7FRZqlk5yOFC9QuXgkwli_VUamdyO7CA7jot06MqFKOu9eQ3jpFS6-dg1jaEEnZyKtk3p71H421tRw8ZginmmMWqsWhycmW-mrtkhKU4eppR6Hf-PGmh9YesLWcXeOsHW_wccF-zsAAP__h8fQhg">