clangd requires manual restart after changes to project settings.

[ReinhardKeil]

Currently it is required to execute manually "clangd: Restart Language Server" in the following situations:

1. A change to .vscode/settings.json:

   "clangd.arguments": [
          "--compile-commands-dir=c:\\Test\\Jan10\\M410_Adc\\ARM\\out\\M410_Adc\\Target_1"
      ]
   }
   

2. A change to the file compile_commands.json that is reference by the .vscode/settings.json. These modifications are the generated by cbuild setup that is called when csolution project files change.

Proposal

Trigger automatically "clangd: Restart Language Server" (clangd.restart) when clangd.arguments or file compile_commands.json change.

[JonatanAntoni]

I'd not expect these files to be modified manually. I.e., no need to put file watches on them. Instead, I can see that these files are repeatedly updated, e.g., by/after cbuild setup.
Doesn't clangd auto-detect changes to its compile_commands.json? If yes, could this be seen as a shortcoming/bug in the clangd extension? Hence, any addition at our end would be a workaround.

What is the test case to replicate the issue and verify a potential fix?
We need to check the version of clangd used. On my Mac I have installed AppleClang 16 and the clangd is taken from this installation.

Relates to: clangd/vscode-clangd#681, clangd/vscode-clangd#300, clangd/vscode-clangd#116

Some aspects we need to check are documented in these issues:

• in any case checks for changes to compile_commands are throttled to ~1/5sec. So if you try to force a check, you can be unlucky: check + overwrite compile_commands + force attempt in quick succession will not see the change
• hopefully you're generating the new file into a new location and renaming: bad things may happen if we see a half-written file
• Restarting the server is kind of a crude way to react to a change, because it comes with a potentially non-trivial performance penalty:
  • the project's index has to be reloaded from disk, and its in-memory representation rebuilt
  • preambles for all open files have to be rebuilt, not just files whose compile command changed
• In clangd 12, "hot reload" of compile_commands.json was implemented on the server side.

[JonatanAntoni]

@brondani: Please check the above statement

hopefully you're generating the new file (compile_commands.json) into a new location and renaming: bad things may happen if we see a half-written file

[brondani]

hopefully you're generating the new file (compile_commands.json) into a new location and renaming: bad things may happen if we see a half-written file

The final location is the output directory which is always the same, but it is done with the CMake command ${CMAKE_COMMAND} -E copy_if_different which should be reasonably solid and does not touch the file when there are no changes.

[ReinhardKeil]

This needs more review from my side.