lsp-watch-root-folder follows symlinks that point outside the root folder

[azuk]

Thank you for the bug report

• I am using the latest version of lsp-mode related packages.
• I checked FAQ and Troubleshooting sections
• You may also try reproduce the issue using clean environment using the following command: M-x lsp-start-plain

Bug description

I was wondering why visiting the first file in a Rust project froze Emacs for a minute or so on a very fast machine, consuming 100% of CPU all that time.

Turns out that lsp-watch-root-folder used for workspace/didChangeWatchedFiles walks the directory recursively using lsp--all-watchable-directories and it follows symlinks even when they point outside the root folder. In my case it ended up traversing the out-of-tree build directory which may contain over 200000 subdirectories IIRC and from there it even found its way to /var/log.

When debugging I also noticed that rust-analyzer provides glob patterns that limit what should actually be watched but lsp-mode seems to ignore them. In a large repository with lots of subprojects this may cause Emacs to watch a lot of unnecessary directories.

Steps to reproduce

• Create for example a Rust project and inside it create a symlink to, say, /var
• Add logging to lsp--all-watchable-directories or put a breakpoint to it using edebug or use some tracing feature.
• Open a file inside the project so that rust-analyzer gets started for the project.
• Observe the directories that lsp--all-watchable-directories traverses.

Expected behavior

• lsp-watch-root-folder does not follow symlinks outside the root folder, at least not by default.
• glob patterns provided by LSP server are used to limit what is watched

Which Language Server did you use?

rust-analyzer

OS

Linux

Error callstack

Anything else?

No response