clangd still cannot find header files after specifying the include options

[iceypotato]

I am using Windows 11, and I have downloaded the gcc compiler from mingw-w64, which should include all the basic system headers, and I am using clangd for vscode.
For some reason, clangd still has a hard time trying to find all the basic header files, even when I specify multiple -isystemC:\path\to\includes. For example, clangd still fails to find bits/c++config.h.
I have made a .clangd file to specify the includes.

CompileFlags:
  Add: [
    -std=c++20,
    "-isystemC:\\Users\\me\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\lib\\gcc\\x86_64-w64-mingw32\\12.2.0\\include",
    "-isystemC:\\Users\\me\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\lib\\gcc\\x86_64-w64-mingw32\\12.2.0\\include\\c++",
    "-isystemC:\\Users\\me\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\lib\\gcc\\x86_64-w64-mingw32\\12.2.0\\include\\c++\\x86_64-w64-mingw32",
    "-isystemC:\\Users\\me\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\include",
    "-isystemC:\\Users\\me\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\x86_64-w64-mingw32\\include"
  ]

Am I missing something?
Sorry if this is not the place to get help with clangd.

[HighCommander4]

Usually using --query-driver(as described towards the end of https://clangd.llvm.org/troubleshooting#cant-find-standard-library-headers-map-stdioh-etc) is an easier way to let clangd find the compiler's built-in includes than specifying them manually.

With this manual approach, I would guess the issue has something to do with the format of the path (e.g. spaces in the path, backslashes, use of quotes, etc. -- getting this stuff right can be tricky, especially on Windows). If you share clangd logs I may be able to offer a more specific diagnosis.

[iceypotato]

I tried the query driver option and put the verbose log option. The query driver did not work. Here is the log from when I restarted the language server and clicked on a file.
clangd verbose.log

[HighCommander4]

A couple of reasons --query-driver is not working in this case:

1. --query-driver currently requires that the project has a compile_commands.json, please see https://clangd.llvm.org/installation#project-setup for ways to create one. (This is more a current limitation than a by-design requirement; I'm working in Detect system include paths when using compile_flags.txt clangd#1089 to relax this such that --query-driver will work with a compiler specified in clangd's config file even in the absence of compile_commands.json.)
2. The argument for --query-driver should be the compiler executable, i.e. ..\bin\g++.exe, not just ..\bin

[iceypotato]

Even with the compile_commands, it still doesn't work. I also fixed --query-driver to point to g++.exe.

This is my compile_commands.json

[
    { 
        "directory": "C:\\Users\\myuser\\Documents\\Visual Studio Code\\C",
        "command": "C:\\Users\\myuser\\Documents\\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\\mingw64\\bin\\g++.exe",
        "file": "*"
    }
]

[HighCommander4]

Hmm, I don't think you can put * in "file", it needs to be a specific file for clangd to find the compile command.

I also wouldn't recommend writing the compile_commands.json manually, it's better to generate it. (Usually I recommend using bear but as I think users have reported it not working on Windows, you could try compiledb instead.)

[iceypotato]

Yep, still no luck. I tried using compiledb, ran the compiledb make command and the outcome was still the same. It generated some stuff inside the compile_commands.json file, but it still could not find bits/c++config.h.

[HighCommander4]

Please show new clangd logs with the generated compile_commands.json.

[iceypotato]

clangd.verbose.log

I did some testing in a VM so the directories have changed.
compile_commands.json:

[
 {
  "directory": "C:\\Users\\myuser\\Documents\\Test",
  "arguments": [
   "g++",
   "-c",
   "-o",
   "testlib.o",
   "testlib.cpp"
  ],
  "file": "testlib.cpp"
 }
]

[HighCommander4]

The logs are showing that:

1. --query-driver is now working, based on the following:

I[13:10:41.424] System includes extractor: successfully executed C:\Users\myuser\Documents\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\mingw64\bin\g++.exe

2. There are no diagnostics issued when you open testlib.cpp.

There are diagnostics issued when you open <iostream>, the reason for that is:

I[13:10:41.362] Failed to find compilation database for c:\Users\myuser\Documents\x86_64-12.2.0-release-posix-seh-rt_v10-rev0\mingw64\lib\gcc\x86_64-w64-mingw32\12.2.0\include\c++\iostream

this can be fixed using https://clangd.llvm.org/faq#how-do-i-fix-errors-i-get-when-opening-headers-outside-of-my-project-directory.

[iceypotato]

Thanks, it was fixed. I also had to add the compilers to my user path also. My question is, is there no other way to do it without a compiler_commands.json? Like, is there a way to do this with the clang user config file (.clangd, clangd.yaml)?

[HighCommander4]

Once clangd/clangd#1089 is fixed, it should be enough to add:

CompileFlags:
  Compiler: /path/to/g++

to the clangd config file (and --query-driver=/path/to/g++ to the clangd command line), and compile_commands.json will not be required.