feat: now, when you're hovering over a require('a.b.c'), you can type gf, and go to the 'c.lua' file (#3122)

ftplugin/lua.lua

@@ -0,0 +1,86 @@
+local fmt = string.format
+
+-- Iterator that splits a string o a given delimiter
+local function split(str, delim)
+  delim = delim or "%s"
+  return string.gmatch(str, fmt("[^%s]+", delim))
+end
+
+-- Find the proper directory separator depending
+-- on lua installation or OS.
+local function dir_separator()
+  -- Look at package.config for directory separator string (it's the first line)
+  if package.config then
+    return string.match(package.config, "^[^\n]")
+  elseif vim.fn.has "win32" == 1 then
+    return "\\"
+  else
+    return "/"
+  end
+end
+
+-- Search for lua traditional include paths.
+-- This mimics how require internally works.
+local function include_paths(fname, ext)
+  ext = ext or "lua"
+  local sep = dir_separator()
+  local paths = string.gsub(package.path, "%?", fname)
+  for path in split(paths, "%;") do
+    if vim.fn.filereadable(path) == 1 then
+      return path
+    end
+  end
+end
+
+-- Search for nvim lua include paths
+local function include_rtpaths(fname, ext)
+  ext = ext or "lua"
+  local sep = dir_separator()
+  local rtpaths = vim.api.nvim_list_runtime_paths()
+  local modfile, initfile = fmt("%s.%s", fname, ext), fmt("init.%s", ext)
+  for _, path in ipairs(rtpaths) do
+    -- Look on runtime path for 'lua/*.lua' files
+    local path1 = table.concat({ path, ext, modfile }, sep)
+    if vim.fn.filereadable(path1) == 1 then
+      return path1
+    end
+    -- Look on runtime path for 'lua/*/init.lua' files
+    local path2 = table.concat({ path, ext, fname, initfile }, sep)
+    if vim.fn.filereadable(path2) == 1 then
+      return path2
+    end
+  end
+end
+
+-- Global function that searches the path for the required file
+function find_required_path(module)
+  -- Look at package.config for directory separator string (it's the first line)
+  local sep = string.match(package.config, "^[^\n]")
+  -- Properly change '.' to separator (probably '/' on *nix and '\' on Windows)
+  local fname = vim.fn.substitute(module, "\\.", sep, "g")
+  local f
+  ---- First search for lua modules
+  f = include_paths(fname, "lua")
+  if f then
+    return f
+  end
+  -- This part is just for nvim modules
+  f = include_rtpaths(fname, "lua")
+  if f then
+    return f
+  end
+  ---- Now search for Fennel modules
+  f = include_paths(fname, "fnl")
+  if f then
+    return f
+  end
+  -- This part is just for nvim modules
+  f = include_rtpaths(fname, "fnl")
+  if f then
+    return f
+  end
+end
+
+-- Set options to open require with gf
+vim.opt_local.include = [=[\v<((do|load)file|require)\s*\(?['"]\zs[^'"]+\ze['"]]=]
+vim.opt_local.includeexpr = "v:lua.find_required_path(v:fname)"