systemlist: add keepempty option to preserve final newline

runtime/doc/eval.txt

@@ -6188,11 +6188,12 @@ system({expr} [, {input}])				*system()* *E677*
 		Use |:checktime| to force a check.
 
 
-systemlist({expr} [, {input}])				*systemlist()*
+systemlist({expr} [, {input} [, {keepempty}]])		*systemlist()*
 		Same as |system()|, but returns a |List| with lines (parts of 
 		output separated by NL) with NULs transformed into NLs. Output 
 		is the same as |readfile()| will output with {binary} argument 
-		set to "b".
+		set to "b", except that a final newline is not preserved,
+		unless {keepempty} is present and it's non-zero.
 
 		Returns an empty string on error, so be careful not to run 
 		into |E706|.

src/nvim/eval.c

@@ -6593,7 +6593,7 @@ static struct fst {
   {"synconcealed",    2, 2, f_synconcealed},
   {"synstack",        2, 2, f_synstack},
   {"system",          1, 2, f_system},
-  {"systemlist",      1, 2, f_systemlist},
+  {"systemlist",      1, 3, f_systemlist},
   {"tabpagebuflist",  0, 1, f_tabpagebuflist},
   {"tabpagenr",       0, 1, f_tabpagenr},
   {"tabpagewinnr",    1, 2, f_tabpagewinnr},
@@ -14523,7 +14523,7 @@ static void f_synstack(typval_T *argvars, typval_T *rettv)
   }
 }
 
-static list_T* string_to_list(char_u *str, size_t len)
+static list_T* string_to_list(char_u *str, size_t len, bool keepempty)
 {
   list_T *list = list_alloc();
 
@@ -14543,6 +14543,11 @@ static list_T* string_to_list(char_u *str, size_t len)
     list_append(list, li);
   }
 
+  // Optionally retain final newline, if present
+  if (keepempty && str[len-1] == NL) {
+      list_append_string(list, (char_u*)"", 0);
+  }
+
   return list;
 }
 
@@ -14585,7 +14590,11 @@ static void get_system_output_as_rettv(typval_T *argvars, typval_T *rettv,
   }
 
   if (retlist) {
-    rettv->vval.v_list = string_to_list((char_u *) res, nread);
+    int keepempty = 0;
+    if (argvars[1].v_type != VAR_UNKNOWN && argvars[2].v_type != VAR_UNKNOWN) {
+      keepempty = get_tv_number(&argvars[2]);
+    }
+    rettv->vval.v_list = string_to_list((char_u *) res, nread, keepempty != 0);
     rettv->vval.v_list->lv_refcount++;
     rettv->v_type = VAR_LIST;
 
@@ -19723,7 +19732,7 @@ static void apply_job_autocmds(int id, char *name, char *type,
     str_slot->li_tv.v_type = VAR_LIST;
     str_slot->li_tv.v_lock = 0;
     str_slot->li_tv.vval.v_list =
-      string_to_list((char_u *) received, received_len);
+      string_to_list((char_u *) received, received_len, false);
     str_slot->li_tv.vval.v_list->lv_refcount++;
     list_append(list, str_slot);
 

test/functional/shell/viml_system_spec.lua

@@ -188,6 +188,18 @@ describe('systemlist()', function()
     end)
   end)
 
+  describe('when keepempty option is', function()
+    it('0, ignores trailing newline', function()
+      eq({'aa','bb'}, eval("systemlist('cat',['aa','bb'],0)"))
+      eq({'aa','bb'}, eval("systemlist('cat',['aa','bb',''],0)"))
+    end)
+
+    it('1, preserves trailing newline', function()
+      eq({'aa','bb'}, eval("systemlist('cat',['aa','bb'],1)"))
+      eq({'aa','bb',''}, eval("systemlist('cat',['aa','bb',''],2)"))
+    end)
+  end)
+
   if xclip then
     describe("with a program that doesn't close stdout", function()
       it('will exit properly after passing input', function()