vimrc: rust-analyzer gd/completion on standalone .rs files

Root rust-analyzer at the owning crate only if the file is one of its
targets; otherwise list the file in detachedFiles (init options for the
first file, workspace config for later ones) so std resolves.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 49 insertions, 1 deletions

diff --git a/core/vimrc b/core/vimrc
index f62115c..a2b40c4 100644
--- a/core/vimrc
+++ b/core/vimrc
@@ -153,20 +153,68 @@ endif
 let g:gitgutter_sign_column_always = 0
 
 
+" rust-analyzer root: nearest Cargo.toml dir only if this file is a target of that crate
+" (src/ examples/ tests/ benches/ build.rs, or its path appears in the manifest); else the
+" file's own dir, so rust-analyzer loads it standalone (std resolves) instead of detached-in-a-foreign-project
+" RustCrate(): crate dir if this buffer is a target of its nearest Cargo.toml, else ''
+function! RustCrate() abort
+  let l:p = expand('%:p')
+  let l:d = lsp#utils#find_nearest_parent_file_directory(l:p, 'Cargo.toml')
+  if !empty(l:d)
+    let l:d = substitute(fnamemodify(l:d, ':p'), '/$', '', '')
+    let l:rel = stridx(l:p, l:d . '/') == 0 ? l:p[len(l:d) + 1:] : ''
+    let l:target = l:rel =~# '^\(src\|examples\|tests\|benches\)/' || l:rel ==# 'build.rs'
+    if !l:target && !empty(l:rel)
+      let l:target = stridx(join(readfile(l:d . '/Cargo.toml'), "\n"), '"' . l:rel . '"') >= 0
+    endif
+    if l:target
+      return l:d
+    endif
+  endif
+  return ''
+endfunction
+function! RustRoot() abort
+  let l:c = RustCrate()
+  return empty(l:c) ? expand('%:p:h') : l:c
+endfunction
+" Standalone .rs files (no owning crate) must be listed in rust-analyzer's detachedFiles,
+" else it loads nothing for them (no gd/completion). The list is shared by reference with
+" the init options below (covers the first file) and pushed as config for later files.
+let g:ra_detached = []
+function! RustDetach() abort
+  if !exists('g:lsp_loaded')
+    return
+  endif
+  let l:p = expand('%:p')
+  if empty(l:p) || !empty(RustCrate()) || index(g:ra_detached, l:p) >= 0
+    return
+  endif
+  call add(g:ra_detached, l:p)
+  if lsp#get_server_status('rust-analyzer') ==# 'running'
+    call lsp#update_workspace_config('rust-analyzer', {'rust-analyzer': {'detachedFiles': copy(g:ra_detached)}})
+  endif
+endfunction
+augroup rust_detached
+  au!
+  au BufEnter *.rs call RustDetach()
+augroup END
+
 " rust-analyzer via the rustup proxy shim (portable across toolchains/machines)
 if executable(expand('~/.cargo/bin/rust-analyzer'))
   au User lsp_setup call lsp#register_server({
   \   'name': 'rust-analyzer',
   \   'cmd': {server_info -> [expand('~/.cargo/bin/rust-analyzer')]},
   \   'allowlist': ['rust'],
-  \   'root_uri': {server_info -> lsp#utils#path_to_uri(lsp#utils#find_nearest_parent_file_directory(lsp#utils#get_buffer_path(), 'Cargo.toml'))},
+  \   'root_uri': {server_info -> lsp#utils#path_to_uri(RustRoot())},
   \   'initialization_options': {
   \     'completion': {
   \       'autoimport': { 'enable': v:true },
   \       'postfix':    { 'enable': v:true },
   \     },
   \     'checkOnSave': v:true,
+  \     'detachedFiles': g:ra_detached,
   \   },
+  \   'workspace_config': {'rust-analyzer': {'detachedFiles': g:ra_detached}},
   \ })
 endif
 if executable(expand('~/.local/bin/ruff'))