feat(lua): in script mode -l, use raw output for print()

consider the following test_script.lua :

    print 'hello\n' -- TWO new lines
    print 'this is \027[31mRED FOR AN AMAZING REASON\027[0m'
    print 'foo'
    print '' -- newline despite empty!
    print 'bar'

    -- a bit later:
    os.execute 'sleep 2' -- CPU goes BRR, cursor in column zero
    print 'more bar'

before this PR, `nvim -l test_script.lua` had some weird behaviors
compared to `lua test_script.lua` or the now removed `nvim -ll
test_script.lua`.

- one extra '\n' at the end of a print is ignored, one would need
  TWO '\n' for a single extra '\n'

- an empty print'' is supposed to print an empty line

- print'\027[31mRED' is being escaped so it does not work

- the cursor gets stuck at the end of a message, instead of after
  emitting the new line, this looks like the CPU lag has something
  to do with the _last_ printed message which is likely not the case.

I consider these behaviors to be unintentional (a consequence of
stragglig through the message.c meta-machine, which is optimized
for message handling in _an interative text editor_) and getting
closer to plain lua behavior would be better.

An alternative would be to restore the builtin print(), but our
implemenation still has some benefits, like try
`print(setmetatable({}, {__tostring=error})` in plain lua..

1 files changed, 12 insertions, 5 deletions

diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index a34f08a36c..a0b982ab0f 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -20,6 +20,7 @@
 #include "nvim/ascii_defs.h"
 #include "nvim/buffer_defs.h"
 #include "nvim/change.h"
+#include "nvim/channel.h"
 #include "nvim/cmdexpand_defs.h"
 #include "nvim/cursor.h"
 #include "nvim/drawscreen.h"
@@ -1117,12 +1118,18 @@ static void nlua_common_free_all_mem(lua_State *lstate)
 
 static void nlua_print_event(void **argv)
 {
-  HlMessage msg = KV_INITIAL_VALUE;
-  HlMessageChunk chunk = { { .data = argv[0], .size = (size_t)(intptr_t)argv[1] - 1 }, 0 };
-  kv_push(msg, chunk);
-  bool needs_clear = false;
   msg_ext_no_fast();
-  msg_multihl(NIL, msg, "lua_print", true, false, NULL, &needs_clear);
+  if (msg_use_printf() && on_print.type == kCallbackNone) {
+    msg_start();  // flush incomplete message
+    printf("%.*s\n", (int)(intptr_t)argv[1] - 1, (char *)argv[0]);
+    xfree(argv[0]);
+  } else {
+    HlMessage msg = KV_INITIAL_VALUE;
+    HlMessageChunk chunk = { { .data = argv[0], .size = (size_t)(intptr_t)argv[1] - 1 }, 0 };
+    kv_push(msg, chunk);
+    bool needs_clear = false;
+    msg_multihl(NIL, msg, "lua_print", true, false, NULL, &needs_clear);
+  }
 }
 
 /// Implements Lua print() as a Nvim message.