fix(chansend): sending lines to terminal in reverse order on Windows #19315

Problem: `chansend()` on Windows sends lines in reverse order.
Cause: Using \n instead of \r\n for newlines on Windows.
Solution: on Windows, use CRLF newline characters.

Fixes #18501

src/nvim/eval.c

@@ -5426,7 +5426,7 @@ void get_system_output_as_rettv(typval_T *argvars, typval_T *rettv, bool retlist
 
   // get input to the shell command (if any), and its length
   ptrdiff_t input_len;
-  char *input = save_tv_as_string(&argvars[1], &input_len, false);
+  char *input = save_tv_as_string(&argvars[1], &input_len, false, false);
   if (input_len < 0) {
     assert(input == NULL);
     return;
@@ -5921,9 +5921,10 @@ bool read_blob(FILE *const fd, blob_T *const blob)
 /// @param[in]  tv   Value to store as a string.
 /// @param[out] len  Length of the resulting string or -1 on error.
 /// @param[in]  endnl If true, the output will end in a newline (if a list).
+/// @param[in]  crlf  If true, list items will be joined with CRLF (if a list).
 /// @returns an allocated string if `tv` represents a VimL string, list, or
 ///          number; NULL otherwise.
-char *save_tv_as_string(typval_T *tv, ptrdiff_t *const len, bool endnl)
+char *save_tv_as_string(typval_T *tv, ptrdiff_t *const len, bool endnl, bool crlf)
   FUNC_ATTR_MALLOC FUNC_ATTR_NONNULL_ALL
 {
   *len = 0;
@@ -5980,20 +5981,23 @@ char *save_tv_as_string(typval_T *tv, ptrdiff_t *const len, bool endnl)
   // Pre-calculate the resulting length.
   list_T *list = tv->vval.v_list;
   TV_LIST_ITER_CONST(list, li, {
-    *len += (ptrdiff_t)strlen(tv_get_string(TV_LIST_ITEM_TV(li))) + 1;
+    *len += (ptrdiff_t)strlen(tv_get_string(TV_LIST_ITEM_TV(li))) + (crlf ? 2 : 1);
   });
 
   if (*len == 0) {
     return NULL;
   }
 
-  char *ret = xmalloc((size_t)(*len) + endnl);
+  char *ret = xmalloc((size_t)(*len) + (endnl ? (crlf ? 2 : 1) : 0));
   char *end = ret;
   TV_LIST_ITER_CONST(list, li, {
     for (const char *s = tv_get_string(TV_LIST_ITEM_TV(li)); *s != NUL; s++) {
       *end++ = (*s == '\n') ? NUL : *s;
     }
     if (endnl || TV_LIST_ITEM_NEXT(list, li) != NULL) {
+      if (crlf) {
+        *end++ = '\r';
+      }
       *end++ = '\n';
     }
   });

src/nvim/eval/funcs.c

@@ -648,6 +648,14 @@ static void f_chansend(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 
   ptrdiff_t input_len = 0;
   char *input = NULL;
+  uint64_t id = (uint64_t)argvars[0].vval.v_number;
+#ifdef UNIX
+  bool crlf = false;
+#else
+  Channel *chan = find_channel(id);
+  bool crlf = (chan != NULL && chan->term) ? true: false;
+#endif
+
   if (argvars[1].v_type == VAR_BLOB) {
     const blob_T *const b = argvars[1].vval.v_blob;
     input_len = tv_blob_len(b);
@@ -655,7 +663,7 @@ static void f_chansend(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
       input = xmemdup(b->bv_ga.ga_data, (size_t)input_len);
     }
   } else {
-    input = save_tv_as_string(&argvars[1], &input_len, false);
+    input = save_tv_as_string(&argvars[1], &input_len, false, crlf);
   }
 
   if (!input) {
@@ -663,7 +671,6 @@ static void f_chansend(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     // or there is no input to send.
     return;
   }
-  uint64_t id = (uint64_t)argvars[0].vval.v_number;
   const char *error = NULL;
   rettv->vval.v_number = (varnumber_T)channel_send(id, input, (size_t)input_len, true, &error);
   if (error) {

test/functional/terminal/channel_spec.lua

@@ -7,6 +7,7 @@ local command = helpers.command
 local pcall_err = helpers.pcall_err
 local feed = helpers.feed
 local poke_eventloop = helpers.poke_eventloop
+local is_os = helpers.is_os
 
 describe('terminal channel is closed and later released if', function()
   local screen
@@ -92,3 +93,17 @@ describe('terminal channel is closed and later released if', function()
     eq(chans - 1, eval('len(nvim_list_chans())'))
   end)
 end)
+
+it('chansend sends lines to terminal channel in proper order', function()
+  clear()
+  local screen = Screen.new(100, 20)
+  screen:attach()
+  local shells = is_os('win') and {'cmd.exe', 'pwsh.exe -nop', 'powershell.exe -nop'} or {'sh'}
+  for _, sh in ipairs(shells) do
+    command([[bdelete! | let id = termopen(']] .. sh .. [[')]])
+    command([[call chansend(id, ['echo "hello"', 'echo "world"', ''])]])
+    screen:expect{
+      any=[[echo "hello".*echo "world"]]
+    }
+  end
+end)