vim-patch:8.0.1734: package directory not added to 'rtp' if prefix matches

Problem:    Package directory not added to 'rtp' if prefix matches.
Solution:   Check the match is a full match. (Ozaki Kiichi, closes vim/vim#2817)
            Also handle different ways of spelling a path.
f98a39ca57

src/nvim/ex_cmds2.c

@@ -2683,12 +2683,26 @@ static int APP_BOTH;
 
 static void add_pack_plugin(char_u *fname, void *cookie)
 {
-  if (cookie != &APP_LOAD && strstr((char *)p_rtp, (char *)fname) == NULL) {
+  if (cookie != &APP_LOAD) {
+    char *buf = xmalloc(MAXPATHL);
+    bool found = false;
+
+    const char *p = (const char *)p_rtp;
+    while (*p != NUL) {
+      copy_option_part((char_u **)&p, (char_u *)buf, MAXPATHL, ",");
+      if (path_fnamecmp(buf, (char *)fname) == 0) {
+        found = true;
+        break;
+      }
+    }
+    xfree(buf);
+    if (!found) {
       // directory is not yet in 'runtimepath', add it
       if (add_pack_dir_to_rtp(fname) == FAIL) {
         return;
       }
     }
+  }
 
   if (cookie != &APP_ADD_DIR) {
     load_pack_plugin(fname);

test/functional/legacy/packadd_spec.lua

@@ -57,6 +57,15 @@ describe('packadd', function()
         call assert_match(Escape(s:plugdir) . '\($\|,\)', &rtp)
         call assert_match(Escape(expand(s:plugdir . '/after$')), &rtp)
 
+        " NOTE: '/.../opt/myte' forwardly matches with '/.../opt/mytest'
+        call mkdir(fnamemodify(s:plugdir, ':h') . '/myte', 'p')
+        let rtp = &rtp
+        packadd myte
+
+        " Check the path of 'myte' is added
+        call assert_true(len(&rtp) > len(rtp))
+        call assert_match(Escape(s:plugdir) . '\($\|,\)', &rtp)
+
         " Check exception
         call assert_fails("packadd directorynotfound", 'E919:')
         call assert_fails("packadd", 'E471:')