copyCompileCommands to the original path makes the file empty

[tocic]

Brief Issue Summary

I'm using cmake.copyCompileCommands as a workaround to support clangd (see #654):

"cmake.copyCompileCommands": "${workspaceFolder}/build/compile_commands.json"

But if the ${workspaceFolder}/build directory is the original compile_commands.json's directory then the extension makes the file empty. I expect it to either not copy the file or overwrite the file with its original contents.

CMake Tools Diagnostics

{
  "os": "linux",
  "vscodeVersion": "1.79.2",
  "cmtVersion": "1.14.33",
  "configurations": [
    {
      "folder": "/home/tocic/test",
      "cmakeVersion": "3.26.4",
      "configured": true,
      "generator": "Ninja",
      "usesPresets": false,
      "compilers": {
        "C": "/usr/bin/gcc",
        "CXX": "/usr/bin/g++"
      }
    }
  ],
  "cpptoolsIntegration": {
    "isReady": false,
    "hasCodeModel": false,
    "activeBuildType": "",
    "buildTypesSeen": [],
    "requests": [],
    "responses": [],
    "partialMatches": [],
    "targetCount": 0,
    "executablesCount": 0,
    "librariesCount": 0,
    "targets": []
  },
  "settings": [
    {
      "communicationMode": "automatic",
      "useCMakePresets": "auto",
      "configureOnOpen": false
    }
  ]
}

Debug Log

[main] Copying compile_commands.json from /home/tocic/test/build/compile_commands.json to /home/tocic/test/build/compile_commands.json
[compdb] Error parsing compilation database "/home/tocic/test/build/compile_commands.json": 
	SyntaxError: Unexpected end of JSON input
	at JSON.parse (<anonymous>)
	at CompilationDatabase.fromFilePaths (/home/tocic/.vscode-oss/extensions/ms-vscode.cmake-tools-1.14.33-universal/dist/main.js:37178:38)
	at async CMakeProject.refreshCompileDatabase (/home/tocic/.vscode-oss/extensions/ms-vscode.cmake-tools-1.14.33-universal/dist/main.js:34944:27)
	at async /home/tocic/.vscode-oss/extensions/ms-vscode.cmake-tools-1.14.33-universal/dist/main.js:35056:33
	at async CMakeProject.doConfigure (/home/tocic/.vscode-oss/extensions/ms-vscode.cmake-tools-1.14.33-universal/dist/main.js:35145:24)

Additional Information

No response

[gcampbell-msft]

@tocic Thanks for the bug report! We will put this on the backlog and assess when we can get to it. In the meantime, we are happy to take open source contributions!

[parniere]

Hi, I just hit the same bug, I think the pull request just posted above fix it
the symptom was a bit hard to see at first, I was on a very large project with clangd configured, and some of my files were not properly analyzed.

After some investigation, I noticed that the compilation db located in workspace/build had a very strange size (65536)
Monitoring this size during cmake generation, and it appeared that the size was corrupted after being properly generated.

[recursivenomad]

I'd like to re-open this issue, as the current solution does not account for differences in path separators on Windows. Example:

"cmake.buildDirectory": "${workspaceFolder}/firmware/build"

on Windows gets sanitized to your/path/to/firmware/build/compile_commands.json. But:

"cmake.copyCompileCommands": "${workspaceFolder}/firmware/build/compile_commands.json"

does not get sanitized on Windows, and results in your\path\to/firmware/build/compile_commands.json. I can confirm this is the problem by manually entering the absolute path with identical path separators as the sanitized input, and the feature will work as intended. The result is there is still CDB corruption on Windows when using ${workspaceFolder}.