vim-patch:8.0.1398: :packadd does not load packages from the "start" directory (#8762)

Problem:    :packadd does not load packages from the "start" directory.
            (Alejandro Hernandez)
Solution:   Make :packadd look in the "start" directory if those packages were
            not loaded on startup.
9e1d399e63

src/nvim/ex_cmds2.c

@@ -2693,14 +2693,27 @@ void ex_packloadall(exarg_T *eap)
 /// ":packadd[!] {name}"
 void ex_packadd(exarg_T *eap)
 {
-  static const char *plugpat = "pack/*/opt/%s";  // NOLINT
+  static const char *plugpat = "pack/*/%s/%s";    // NOLINT
+  int res = OK;
 
-  size_t len = STRLEN(plugpat) + STRLEN(eap->arg);
-  char *pat = (char *)xmallocz(len);
-  vim_snprintf(pat, len, plugpat, eap->arg);
-  do_in_path(p_pp, (char_u *)pat, DIP_ALL + DIP_DIR + DIP_ERR, add_pack_plugin,
-             eap->forceit ? &APP_ADD_DIR : &APP_BOTH);
-  xfree(pat);
+  // Round 1: use "start", round 2: use "opt".
+  for (int round = 1; round <= 2; round++) {
+    // Only look under "start" when loading packages wasn't done yet.
+    if (round == 1 && did_source_packages) {
+      continue;
+    }
+
+    const size_t len = STRLEN(plugpat) + STRLEN(eap->arg) + 5;
+    char *pat = xmallocz(len);
+    vim_snprintf(pat, len, plugpat, round == 1 ? "start" : "opt", eap->arg);
+    // The first round don't give a "not found" error, in the second round
+    // only when nothing was found in the first round.
+    res = do_in_path(p_pp, (char_u *)pat,
+                     DIP_ALL + DIP_DIR
+                     + (round == 2 && res == FAIL ? DIP_ERR : 0),
+                     add_pack_plugin, eap->forceit ? &APP_ADD_DIR : &APP_BOTH);
+    xfree(pat);
+  }
 }
 
 /// ":options"

test/functional/legacy/packadd_spec.lua

@@ -58,6 +58,24 @@ describe('packadd', function()
         call assert_fails("packadd", 'E471:')
       endfunc
 
+      func Test_packadd_start()
+        let plugdir = expand(s:topdir . '/pack/mine/start/other')
+        call mkdir(plugdir . '/plugin', 'p')
+        set rtp&
+        let rtp = &rtp
+        filetype on
+
+        exe 'split ' . plugdir . '/plugin/test.vim'
+        call setline(1, 'let g:plugin_works = 24')
+        wq
+
+        packadd other
+
+        call assert_equal(24, g:plugin_works)
+        call assert_true(len(&rtp) > len(rtp))
+        call assert_true(&rtp =~ (escape(plugdir, '\') . '\($\|,\)'))
+      endfunc
+
       func Test_packadd_noload()
         call mkdir(s:plugdir . '/plugin', 'p')
         call mkdir(s:plugdir . '/syntax', 'p')
@@ -286,6 +304,11 @@ describe('packadd', function()
     expected_empty()
   end)
 
+  it('loads packages from "start" directory', function()
+    call('Test_packadd_start')
+    expected_empty()
+  end)
+
   describe('command line completion', function()
     local Screen = require('test.functional.ui.screen')
     local screen