patch 9.0.0865: duplicate arguments are not always detected

Problem:    Duplicate arguments are not always detected.
Solution:   Expand to full path before comparing arguments. (Nir Lichtman,
            closes #11505, closes #9402)

src/arglist.c

@@ -784,9 +784,25 @@ ex_argdedupe(exarg_T *eap UNUSED)
     int j;
 
     for (i = 0; i < ARGCOUNT; ++i)
-	for (j = i + 1; j < ARGCOUNT; ++j)
-	    if (fnamecmp(ARGLIST[i].ae_fname, ARGLIST[j].ae_fname) == 0)
     {
+	// Expand each argument to a full path to catch different paths leading
+	// to the same file.
+	char_u *firstFullname = FullName_save(ARGLIST[i].ae_fname, FALSE);
+	if (firstFullname == NULL)
+	    return;  // out of memory
+
+	for (j = i + 1; j < ARGCOUNT; ++j)
+	{
+	    char_u *secondFullname = FullName_save(ARGLIST[j].ae_fname, FALSE);
+	    if (secondFullname == NULL)
+		break;  // out of memory
+	    int areNamesDuplicate =
+				  fnamecmp(firstFullname, secondFullname) == 0;
+	    vim_free(secondFullname);
+
+	    if (areNamesDuplicate)
+	    {
+		// remove one duplicate argument
 		vim_free(ARGLIST[j].ae_fname);
 		mch_memmove(ARGLIST + j, ARGLIST + j + 1,
 					(ARGCOUNT - j - 1) * sizeof(aentry_T));
@@ -801,6 +817,10 @@ ex_argdedupe(exarg_T *eap UNUSED)
 	    }
 	}
 
+	vim_free(firstFullname);
+    }
+}
+
 /*
  * ":argedit"
  */

src/testdir/test_arglist.vim

@@ -420,15 +420,19 @@ func Test_argdedupe()
   call Reset_arglist()
   argdedupe
   call assert_equal([], argv())
+
   args a a a aa b b a b aa
   argdedupe
   call assert_equal(['a', 'aa', 'b'], argv())
+
   args a b c
   argdedupe
   call assert_equal(['a', 'b', 'c'], argv())
+
   args a
   argdedupe
   call assert_equal(['a'], argv())
+
   args a A b B
   argdedupe
   if has('fname_case')
@@ -436,11 +440,17 @@ func Test_argdedupe()
   else
     call assert_equal(['a', 'b'], argv())
   endif
+
   args a b a c a b
   last
   argdedupe
   next
   call assert_equal('c', expand('%:t'))
+
+  args a ./a
+  argdedupe
+  call assert_equal(['a'], argv())
+
   %argd
 endfunc
 

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    865,
 /**/
     864,
 /**/