vim-patch:8.0.0642: writefile() continues after detecting an error

Problem:    writefile() continues after detecting an error.
Solution:   Bail out as soon as an error is detected. (suggestions by Nikolai
            Pavlov, closes vim/vim#1476)
https://github.com/vim/vim/commit/8cf91286ca46a501d24e4b7d631b193256782c88

2 files changed, 27 insertions, 5 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 86ed9052aa..8d45863d6f 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -17675,7 +17675,7 @@ static void f_wordcount(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 /// "writefile()" function
 static void f_writefile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
-  rettv->vval.v_number = 0;  // Assuming success.
+  rettv->vval.v_number = -1;
 
   if (check_restricted() || check_secure()) {
     return;
@@ -17685,6 +17685,12 @@ static void f_writefile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     EMSG2(_(e_listarg), "writefile()");
     return;
   }
+  const list_T *const list = argvars[0].vval.v_list;
+  TV_LIST_ITER_CONST(list, li, {
+    if (!tv_check_str_or_nr(TV_LIST_ITEM_TV(li))) {
+      return;
+    }
+  });
 
   bool binary = false;
   bool append = false;
@@ -17716,7 +17722,6 @@ static void f_writefile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   }
   FileDescriptor fp;
   int error;
-  rettv->vval.v_number = -1;
   if (*fname == NUL) {
     EMSG(_("E482: Can't open file with an empty name"));
   } else if ((error = file_open(&fp, fname,
@@ -17725,7 +17730,7 @@ static void f_writefile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     emsgf(_("E482: Can't open file %s for writing: %s"),
           fname, os_strerror(error));
   } else {
-    if (write_list(&fp, argvars[0].vval.v_list, binary)) {
+    if (write_list(&fp, list, binary)) {
       rettv->vval.v_number = 0;
     }
     if ((error = file_close(&fp, do_fsync)) != 0) {
diff --git a/src/nvim/testdir/test_writefile.vim b/src/nvim/testdir/test_writefile.vim
index d820c580ac..13c1a888d9 100644
--- a/src/nvim/testdir/test_writefile.vim
+++ b/src/nvim/testdir/test_writefile.vim
@@ -1,5 +1,6 @@
+" Tests for the writefile() function.
 
-function! Test_WriteFile()
+func Test_writefile()
   let f = tempname()
   call writefile(["over","written"], f, "b")
   call writefile(["hello","world"], f, "b")
@@ -13,4 +14,20 @@ function! Test_WriteFile()
   call assert_equal("morning", l[3])
   call assert_equal("vimmers", l[4])
   call delete(f)
-endfunction
+endfunc
+
+func Test_writefile_fails_gently()
+  call assert_fails('call writefile(["test"], "Xfile", [])', 'E730:')
+  call assert_false(filereadable("Xfile"))
+  call delete("Xfile")
+
+  call assert_fails('call writefile(["test", [], [], [], "tset"], "Xfile")', 'E730:')
+  call assert_false(filereadable("Xfile"))
+  call delete("Xfile")
+
+  call assert_fails('call writefile([], "Xfile", [])', 'E730:')
+  call assert_false(filereadable("Xfile"))
+  call delete("Xfile")
+
+  call assert_fails('call writefile([], [])', 'E730:')
+endfunc