[clangd] clangd doesn't work with some file names with --experimental-modules-support option

[FSK-idk]

Here I have an example repo: https://github.com/FSK-idk/clangd-test

When I build the project and look at the file somefile.cppm in particular, I don't see any clangd info:

 

However, if I do one of the following, the info will come back:

• comment import std; in the file types.cppm
• rename the file somefile.cppm, for example, to asd.cppm (or to some other name, but there is a chance that clangd will not work with the new name either)
• add a new file asd.cppm with the content export module asd; (same here, maybe some other name)
• remove --experimental-modules-support option (but then module info won't be available, but at least highlight will work)

Here is what it looks like if I rename somefile.cppm to asd.cppm:

 

Versions

❯ clangd --version
clangd version 20.1.7
Features: linux
Platform: x86_64-pc-linux-gnu
❯ clang --version 
clang version 20.1.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

I also tested it with 21.0.0git version I built today and got the same result.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: FSK (FSK-idk)

Here I have an example repo: https://github.com/FSK-idk/clangd-test

When I build the project and look at the file somefile.cppm in particular, I don't see any clangd info:

<img width="1332" height="306" alt="Image" src="https://github.com/user-attachments/assets/4c239d9c-95cf-4970-930b-62a59affeb72" />
&nbsp;

However, if I do one of the following, the info will come back:

• comment import std; in the file types.cppm
• rename the file somefile.cppm, for example, to asd.cppm (or to some other name, but there is a chance that clangd will not work with the new name either)
• add a new file asd.cppm with the content export module asd; (same here, maybe some other name)
• remove --experimental-modules-support option (but then module info won't be available, but at least highlight will work)

Here is what it looks like if I rename somefile.cppm to asd.cppm:

<img width="1331" height="310" alt="Image" src="https://github.com/user-attachments/assets/544df3f1-65bd-4836-94d9-e56a712c1291" />
&nbsp;

Versions

❯ clangd --version
clangd version 20.1.7
Features: linux
Platform: x86_64-pc-linux-gnu
❯ clang --version 
clang version 20.1.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

I also tested it with 21.0.0git version I built today and got the same result.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: FSK (FSK-idk)

Here I have an example repo: https://github.com/FSK-idk/clangd-test

When I build the project and look at the file somefile.cppm in particular, I don't see any clangd info:

<img width="1332" height="306" alt="Image" src="https://github.com/user-attachments/assets/4c239d9c-95cf-4970-930b-62a59affeb72" />
&nbsp;

However, if I do one of the following, the info will come back:

• comment import std; in the file types.cppm
• rename the file somefile.cppm, for example, to asd.cppm (or to some other name, but there is a chance that clangd will not work with the new name either)
• add a new file asd.cppm with the content export module asd; (same here, maybe some other name)
• remove --experimental-modules-support option (but then module info won't be available, but at least highlight will work)

Here is what it looks like if I rename somefile.cppm to asd.cppm:

<img width="1331" height="310" alt="Image" src="https://github.com/user-attachments/assets/544df3f1-65bd-4836-94d9-e56a712c1291" />
&nbsp;

Versions

❯ clangd --version
clangd version 20.1.7
Features: linux
Platform: x86_64-pc-linux-gnu
❯ clang --version 
clang version 20.1.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

I also tested it with 21.0.0git version I built today and got the same result.