Root-level compile_commands.json required for simple CMake projects

[ADKaster]

Describe the bug

I can only get the VsCode plugin to recognize my project if there is a compile_commands.json at the root level. In any reasonable CMake project, the CMake -B flag is used to provide an out-of-source build directory. Alternatively, a build directory is created and projects specify that developers should invoke cmake .. to pass the source directory as the project root. In either case, the compile_commands.json file will always exist in a subdirectory of the repository, and never at the root. Requiring a symlink into one's build directory for the plugin to work is tedious.

To Reproduce Create the following test project:

CMakeLists.txt

cmake_minimum_required(VERSION 3.25)

project(TestApp LANGUAGES Swift)

set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

add_executable(TestApp main.swift)

main.swift

print("Hello, world!")

.sourcekit-lsp/config.json

{
   "compilationDatabase": {
      "searchPaths": [ "out" ]
   }
}

build the project with

cmake -Bout -GNinja
ninja -Cout

Open the project in vscode

code .

Open main.swift, and observe errors

Inspect the Swift output tab, and see that there is no "focus" displayed:

18:56:06: Activating Swift for Visual Studio Code...
18:56:06: SourceKit-LSP setup
18:56:06: focus: undefined

Symlink out/compile_commands.json to the root of the directory:

ln -s out/compile_commands.json compile_commands.json

And reload the plugin, and you can see that the focus is correctly applied:

19:07:54: Activating Swift for Visual Studio Code...
19:07:54: SourceKit-LSP setup
19:07:54: lsp-weird-stuff: add: /home/andrew/ladybird-org/swift-test-apps/lsp-weird-stuff
19:07:54: lsp-weird-stuff: focus: /home/andrew/ladybird-org/swift-test-apps/lsp-weird-stuff

Expected behavior

As far as I can tell, there is some kind of circular logic going on here. The config.json in .sourcekit-lsp appears to never be loaded. Peeking at SourceKit-LSP's code, it seems that it will only detect a "compile commands workspace" when it finds a compile_commands.json? And all of the "here's how you find compile commands.json" directives (command line, config) require paths 'relative to workspace root'. But if it only finds the workspace root after finding a compile_commands.json, how am I supposed to instruct the project to find compile_commands.json in a subdirectory?

In any case, I expect that vscode-swift should be instructing the LSP that when I open a directory as a project, that directory is the "Workspace root", even if there's no "VsCode workspace" involved. I don't use that feature at all in any of my projects and clangd works fine :).

My config should be loaded as relative to the opened folder, and I shouldn't have to symlink my compile_commands.json to the project root in order for sourcekit-lsp to find it.

Environment

• OS: Ubuntu 24.04
• Swift version 6.2-dev (LLVM 162ee50b401fff2, Swift 57288d13c9f3c02), aka main-snapshot-2025-03-14 from swiftly
• Visual Studio Code version: 1.98.2 ddc367ed5c8936efe395cffeec279b04ffd7db78 x64
• vscode-swift version: 2.0.2

Additional context https://github.com/swiftlang/sourcekit-lsp/issues/1816 rdar://139673190

[award999]

Should be configurable for sourcekit-lsp, we just need to expose a configuration

[ADKaster]

#1484 doesn't solve the general problem here.

My compile_commands.json doesn't live in out or build from the top level in my main work projects. It lives in Build/<configname> or similar.

I would have expected a general solution to actually force the LSP to read the .sourcekit-lsp/config.json in a subdirectory of the 'open folder' or some such.

From the issue description:

In any case, I expect that vscode-swift should be instructing the LSP that when I open a directory as a project, that directory is the "Workspace root", even if there's no "VsCode workspace" involved. I don't use that feature at all in any of my projects and clangd works fine :).

My config should be loaded as relative to the opened folder, and I shouldn't have to symlink my compile_commands.json to the project root in order for sourcekit-lsp to find it.

cc @award999

[andre-richter]

@ADKaster does creating and/or adding the following to $ROOT/.vscode/settings.json help in your case?

{
    "swift.sourcekit-lsp.serverArguments": [
        "--compilation-db-search-path",
        "out"
    ]
}

[matthewbastien]

Re-opening this as the original issue was not actually addressed by the PR. Needs a bit more investigation, but the workaround is to use "swift.sourcekit-lsp.serverArguments" as @andre-richter pointed out (thanks for looking into this!).

At the very least we need better documentation around how to get the extension working with CMake.