patch 8.0.1708: mkdir with 'p' flag fails on existing directory

Problem:    Mkdir with 'p' flag fails on existing directory, which is
            different from the mkdir shell command.
Solution:   Don't fail if the directory already exists. (James McCoy,
            closes #2775)

runtime/doc/eval.txt

@@ -6138,6 +6138,8 @@ mkdir({name} [, {path} [, {prot}]])
 		Example: >
 			:call mkdir($HOME . "/tmp/foo/bar", "p", 0700)
 <		This function is not available in the |sandbox|.
+		There is no error if the directory already exists and the "p"
+		flag is passed (since patch 8.0.1708).
 		Not available on all systems.  To check use: >
 			:if exists("*mkdir")
 <

src/evalfunc.c

@@ -8057,9 +8057,8 @@ f_mkdir(typval_T *argvars, typval_T *rettv)
 
     dir = get_tv_string_buf(&argvars[0], buf);
     if (*dir == NUL)
-	rettv->vval.v_number = FAIL;
+	return;
-    else
+
-    {
     if (*gettail(dir) == NUL)
 	/* remove trailing slashes */
 	*gettail_sep(dir) = NUL;
@@ -8067,12 +8066,23 @@ f_mkdir(typval_T *argvars, typval_T *rettv)
     if (argvars[1].v_type != VAR_UNKNOWN)
     {
 	if (argvars[2].v_type != VAR_UNKNOWN)
+	{
 	    prot = (int)get_tv_number_chk(&argvars[2], NULL);
-	    if (prot != -1 && STRCMP(get_tv_string(&argvars[1]), "p") == 0)
+	    if (prot == -1)
+		return;
+	}
+	if (STRCMP(get_tv_string(&argvars[1]), "p") == 0)
+	{
+	    if (mch_isdir(dir))
+	    {
+		/* With the "p" flag it's OK if the dir already exists. */
+		rettv->vval.v_number = OK;
+		return;
+	    }
 	    mkdir_recurse(dir, prot);
 	}
-	rettv->vval.v_number = prot == -1 ? FAIL : vim_mkdir_emsg(dir, prot);
     }
+    rettv->vval.v_number = vim_mkdir_emsg(dir, prot);
 }
 #endif
 

src/testdir/test_eval_stuff.vim

@@ -25,3 +25,20 @@ func Test_nocatch_restore_silent_emsg()
   let c5 = nr2char(screenchar(&lines, 5))
   call assert_equal('wrong', c1 . c2 . c3 . c4 . c5)
 endfunc
+
+func Test_mkdir_p()
+  call mkdir('Xmkdir/nested', 'p')
+  call assert_true(isdirectory('Xmkdir/nested'))
+  try
+    " Trying to make existing directories doesn't error
+    call mkdir('Xmkdir', 'p')
+    call mkdir('Xmkdir/nested', 'p')
+  catch /E739:/
+    call assert_report('mkdir(..., "p") failed for an existing directory')
+  endtry
+  " 'p' doesn't suppress real errors
+  call writefile([], 'Xfile')
+  call assert_fails('call mkdir("Xfile", "p")', 'E739')
+  call delete('Xfile')
+  call delete('Xmkdir', 'rf')
+endfunc

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1708,
 /**/
     1707,
 /**/