fix(pack): actually checkout proper version of submodules

Problem: Installing plugin with submodules doesn't check out their
  state (due to `git clone --no-checkout` to not end up with default
  branch code in case of invalid `version`).

  Updating a plugin with submodules doesn't update their state.

Solution: Update `git_checkout` helper to account for submodules.
  Another approach would be `git checkout --recurse-submodules ...`,
  but that doesn't seem to allow `--filter=blob:none` for submodules,
  which is nice to have.

  Also make `git_clone` wrapper simpler since `--no-checkout` makes
  `--recurse-submodules` and `--also-filter-submodules` do nothing.

runtime/lua/vim/pack.lua

@@ -264,17 +264,12 @@ end
 --- @param url string
 --- @param path string
 local function git_clone(url, path)
-  local cmd = { 'clone', '--quiet', '--no-checkout', '--recurse-submodules' }
+  local cmd = { 'clone', '--quiet', '--no-checkout' }
 
   if vim.startswith(url, 'file://') then
     cmd[#cmd + 1] = '--no-hardlinks'
-  else
-    if git_version >= vim.version.parse('2.36') then
-      cmd[#cmd + 1] = '--filter=blob:none'
-      cmd[#cmd + 1] = '--also-filter-submodules'
-    elseif git_version >= vim.version.parse('2.27') then
-      cmd[#cmd + 1] = '--filter=blob:none'
-    end
+  elseif git_version >= vim.version.parse('2.27') then
+    cmd[#cmd + 1] = '--filter=blob:none'
   end
 
   vim.list_extend(cmd, { '--origin', 'origin', url, path })
@@ -669,6 +664,12 @@ local function checkout(p, timestamp, skip_stash)
 
   git_cmd({ 'checkout', '--quiet', p.info.sha_target }, p.path)
 
+  local submodule_cmd = { 'submodule', 'update', '--init', '--recursive' }
+  if git_version >= vim.version.parse('2.36') then
+    submodule_cmd[#submodule_cmd + 1] = '--filter=blob:none'
+  end
+  git_cmd(submodule_cmd, p.path)
+
   plugin_lock.plugins[p.spec.name].rev = p.info.sha_target
 
   -- (Re)Generate help tags according to the current help files.

test/functional/plugin/pack_spec.lua

@@ -221,6 +221,34 @@ function repos_setup.semver()
   add_tag('v1.0.0')
 end
 
+function repos_setup.with_subs()
+  -- To-be-submodule repo
+  init_test_repo('sub')
+
+  repo_write_file('sub', 'sub.lua', 'return "sub init"')
+  git_add_commit('Initial commit for "sub"', 'sub')
+
+  -- With-submodules repo with submodule recorded at its initial commit
+  init_test_repo('with_subs')
+
+  repo_write_file('with_subs', 'lua/with_subs.lua', 'return "with_subs init"')
+  local sub_src = 'file://' .. repo_get_path('sub')
+  git_cmd({ '-c', 'protocol.file.allow=always', 'submodule', 'add', sub_src, 'sub' }, 'with_subs')
+  git_add_commit('Initial commit for "with_subs"', 'with_subs')
+  git_cmd({ 'tag', 'init-commit' }, 'with_subs')
+
+  -- Advance both submodule and with-submodules repos by one commit
+  repo_write_file('sub', 'sub.lua', 'return "sub main"')
+  git_add_commit('Second commit for "sub"', 'sub')
+
+  repo_write_file('with_subs', 'lua/with_subs.lua', 'return "with_subs main"')
+  git_cmd(
+    { '-c', 'protocol.file.allow=always', 'submodule', 'update', '--remote', 'sub' },
+    'with_subs'
+  )
+  git_add_commit('Second commit for "with_subs"', 'with_subs')
+end
+
 -- Utility --------------------------------------------------------------------
 
 local function watch_events(event)
@@ -319,6 +347,25 @@ local function mock_confirm(output_value)
   end)
 end
 
+local function mock_git_file_transport()
+  -- HACK: mock `vim.system()` to have `git` commands be executed
+  -- with temporarily set 'protocol.file.allow=always' option.
+  -- Otherwise performing `git` operations with submodules from `vim.pack`
+  -- itself will fail with `fatal: transport 'file' not allowed`.
+  -- Directly adding `-c protocol.file.allow=always` to `git_cmd` in `vim.pack`
+  -- itself is too much and might be bad for security.
+  exec_lua(function()
+    local vim_system_orig = vim.system
+    vim.system = function(cmd, opts, on_exit)
+      if cmd[1] == 'git' then
+        table.insert(cmd, 2, '-c')
+        table.insert(cmd, 3, 'protocol.file.allow=always')
+      end
+      return vim_system_orig(cmd, opts, on_exit)
+    end
+  end)
+end
+
 local function is_jit()
   return exec_lua('return package.loaded.jit ~= nil')
 end
@@ -787,6 +834,16 @@ describe('vim.pack', function()
       eq(false, vim.tbl_contains(rtp, after_dir))
     end)
 
+    it('installs with submodules', function()
+      mock_git_file_transport()
+      exec_lua(function()
+        vim.pack.add({ repos_src.with_subs })
+      end)
+
+      local sub_lua_file = vim.fs.joinpath(pack_get_plug_path('with_subs'), 'sub', 'sub.lua')
+      eq('return "sub main"', fn.readblob(sub_lua_file))
+    end)
+
     it('does not install on bad `version`', function()
       local err = pcall_err(exec_lua, function()
         vim.pack.add({ { src = repos_src.basic, version = 'not-exist' } })
@@ -1662,6 +1719,25 @@ describe('vim.pack', function()
       eq('return "fetch new 2"', fn.readblob(fetch_lua_file))
     end)
 
+    it('works with submodules', function()
+      mock_git_file_transport()
+      exec_lua(function()
+        vim.pack.add({ { src = repos_src.with_subs, version = 'init-commit' } })
+      end)
+
+      local sub_lua_file = vim.fs.joinpath(pack_get_plug_path('with_subs'), 'sub', 'sub.lua')
+      eq('return "sub init"', fn.readblob(sub_lua_file))
+
+      n.clear()
+      mock_git_file_transport()
+      exec_lua(function()
+        vim.pack.add({ repos_src.with_subs })
+        vim.pack.update({ 'with_subs' })
+      end)
+      n.exec('write')
+      eq('return "sub main"', fn.readblob(sub_lua_file))
+    end)
+
     it('can force update', function()
       exec_lua(function()
         vim.pack.add({ repos_src.fetch })