feat(fs): add vim.fs.find()

This is a pure Lua implementation of the Vim findfile() and finddir()
functions without the special syntax.

runtime/lua/vim/fs.lua

@@ -61,4 +61,121 @@ function M.dir(path)
   end, vim.loop.fs_scandir(path)
 end
 
+--- Find files or directories in the given path.
+---
+--- Finds any files or directories given in {names} starting from {path}. If
+--- {upward} is "true" then the search traverses upward through parent
+--- directories; otherwise, the search traverses downward. Note that downward
+--- searches are recursive and may search through many directories! If {stop}
+--- is non-nil, then the search stops when the directory given in {stop} is
+--- reached. The search terminates when {limit} (default 1) matches are found.
+--- The search can be narrowed to find only files or or only directories by
+--- specifying {type} to be "file" or "directory", respectively.
+---
+---@param names (string|table) Names of the files and directories to find. Must
+---             be base names, paths and globs are not supported.
+---@param opts (table) Optional keyword arguments:
+---                       - path (string): Path to begin searching from. If
+---                              omitted, the current working directory is used.
+---                       - upward (boolean, default false): If true, search
+---                                upward through parent directories. Otherwise,
+---                                search through child directories
+---                                (recursively).
+---                       - stop (string): Stop searching when this directory is
+---                              reached. The directory itself is not searched.
+---                       - type (string): Find only files ("file") or
+---                              directories ("directory"). If omitted, both
+---                              files and directories that match {name} are
+---                              included.
+---                       - limit (number, default 1): Stop the search after
+---                               finding this many matches. Use `math.huge` to
+---                               place no limit on the number of matches.
+---@return (table) The paths of all matching files or directories
+function M.find(names, opts)
+  opts = opts or {}
+  vim.validate({
+    names = { names, { 's', 't' } },
+    path = { opts.path, 's', true },
+    upward = { opts.upward, 'b', true },
+    stop = { opts.stop, 's', true },
+    type = { opts.type, 's', true },
+    limit = { opts.limit, 'n', true },
+  })
+
+  names = type(names) == 'string' and { names } or names
+
+  local path = opts.path or vim.loop.cwd()
+  local stop = opts.stop
+  local limit = opts.limit or 1
+
+  local matches = {}
+
+  ---@private
+  local function add(match)
+    matches[#matches + 1] = match
+    if #matches == limit then
+      return true
+    end
+  end
+
+  if opts.upward then
+    ---@private
+    local function test(p)
+      local t = {}
+      for _, name in ipairs(names) do
+        local f = p .. '/' .. name
+        local stat = vim.loop.fs_stat(f)
+        if stat and (not opts.type or opts.type == stat.type) then
+          t[#t + 1] = f
+        end
+      end
+
+      return t
+    end
+
+    for _, match in ipairs(test(path)) do
+      if add(match) then
+        return matches
+      end
+    end
+
+    for parent in M.parents(path) do
+      if stop and parent == stop then
+        break
+      end
+
+      for _, match in ipairs(test(parent)) do
+        if add(match) then
+          return matches
+        end
+      end
+    end
+  else
+    local dirs = { path }
+    while #dirs > 0 do
+      local dir = table.remove(dirs, 1)
+      if stop and dir == stop then
+        break
+      end
+
+      for other, type in M.dir(dir) do
+        local f = dir .. '/' .. other
+        for _, name in ipairs(names) do
+          if name == other and (not opts.type or opts.type == type) then
+            if add(f) then
+              return matches
+            end
+          end
+        end
+
+        if type == 'directory' then
+          dirs[#dirs + 1] = f
+        end
+      end
+    end
+  end
+
+  return matches
+end
+
 return M