feat(vim.fs): abspath({cwd, plain}) #40597

Adds optional parameters to `vim.fs.abspath`:
1. `cwd` to specify directory akin to `--relative-from` in `realpath(1)`.
2. `plain` disables expansion of tilde (~) in paths.

runtime/lua/vim/fs.lua

@@ -865,21 +865,37 @@ function M.rm(path, opts)
   end
 end
 
---- Converts `path` to an absolute path. Expands tilde (~) at the beginning of the path
---- to the user's home directory. Does not check if the path exists, normalize the path, resolve
---- symlinks or hardlinks (including `.` and `..`), or expand environment variables. If the path is
---- already absolute, it is returned unchanged. Also converts `\` path separators to `/`.
+--- @class vim.fs.abspath.Opts
+--- @inlinedoc
+---
+--- Resolve the path relative to this directory.
+--- @field cwd? string
+---
+--- Do not expand tilde (~).
+--- @field plain? boolean
+
+--- Converts `path` to an absolute path. Expands tilde (~) at the beginning of the path (unless
+--- plain=true). Does not check if the path exists, normalize the path, resolve symlinks or
+--- hardlinks (including "." and ".."), or expand environment variables. If the path is already
+--- absolute, it is returned unchanged. Converts `\` path separators to `/`.
 ---
 --- @since 13
 --- @param path string Path
+--- @param opts? vim.fs.abspath.Opts
 --- @return string Absolute path
-function M.abspath(path)
+function M.abspath(path, opts)
   -- TODO(justinmk): mark f_fnamemodify as API_FAST and use it, ":p:h" should be safe...
+  --
+  opts = opts or {}
 
   vim.validate('path', path, 'string')
+  vim.validate('cwd', opts.cwd, 'string', true)
+  vim.validate('plain', opts.plain, 'boolean', true)
 
   -- Expand ~ to user's home directory
-  path = expand_home(path)
+  if not opts.plain then
+    path = expand_home(path)
+  end
 
   -- Convert path separator to `/`
   path = path:gsub(os_sep, '/')
@@ -897,7 +913,8 @@ function M.abspath(path)
 
   -- Windows allows paths like C:foo/bar, these paths are relative to the current working directory
   -- of the drive specified in the path
-  local cwd = assert((iswin and prefix:match('^%w:$')) and uv.fs_realpath(prefix) or uv.cwd())
+  local cwd =
+    assert((iswin and prefix:match('^%w:$')) and uv.fs_realpath(prefix) or opts.cwd or uv.cwd())
   -- Convert cwd path separator to `/`
   cwd = cwd:gsub(os_sep, '/')