From 8ab934287cc010e38e3ec30590805e4ef78404bd Mon Sep 17 00:00:00 2001
From: frazze-jobb <frazze@erlang.org>
Date: Thu, 4 Jul 2024 16:01:02 +0200
Subject: [PATCH] kernel: "overwrite prompt" setting

adds a setting -stdlib shell_bgmsg_location (above|below)
where above means output bg processes io:format above the prompt
and below means output bg processes io:format on the prompt, disturbing
the current line, requiring a redraw to see the whole prompt

also removing code from prim_tty which was a redundant implementation
of what group does when receiving "io_request" during a get_line
---
 lib/kernel/src/group.erl                    | 14 +++++++++++---
 lib/kernel/src/prim_tty.erl                 | 14 ++------------
 lib/kernel/test/interactive_shell_SUITE.erl | 13 +++++++++++++
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/lib/kernel/src/group.erl b/lib/kernel/src/group.erl
index 1792ffe2fb25..138a9f51fa0c 100644
--- a/lib/kernel/src/group.erl
+++ b/lib/kernel/src/group.erl
@@ -818,9 +818,17 @@ more_data(What, Cont0, Drv, Shell, Ls, Encoding) ->
             get_line1(edlin:edit_line(eof, Cont0), Drv, Shell, Ls, Encoding);
         {io_request,From,ReplyAs,Req} when is_pid(From) ->
             {more_chars,Cont,_More} = edlin:edit_line([], Cont0),
-            send_drv_reqs(Drv, edlin:erase_line()),
-            io_request(Req, From, ReplyAs, Drv, Shell, []), %WRONG!!!
-            send_drv_reqs(Drv, edlin:redraw_line(Cont)),
+            Location = application:get_env(stdlib,
+                                           shell_bgmsg_location,
+                                           above),
+            case Location of
+                above ->
+                    send_drv_reqs(Drv, edlin:erase_line()),
+                    io_request(Req, From, ReplyAs, Drv, Shell, []), %WRONG!!!
+                    send_drv_reqs(Drv, edlin:redraw_line(Cont));
+                _ ->
+                    io_request(Req, From, ReplyAs, Drv, Shell, [])
+            end,
             get_line1({more_chars,Cont,[]}, Drv, Shell, Ls, Encoding);
         {reply,{From,ReplyAs},Reply} ->
             %% We take care of replies from puts here as well
diff --git a/lib/kernel/src/prim_tty.erl b/lib/kernel/src/prim_tty.erl
index 5b402c0236e6..cfab2d22d6e9 100644
--- a/lib/kernel/src/prim_tty.erl
+++ b/lib/kernel/src/prim_tty.erl
@@ -633,18 +633,8 @@ handle_request(State, {expand_with_trim, Binary}) ->
 %% putc prints Binary and overwrites any existing characters
 handle_request(State = #state{ unicode = U }, {putc, Binary}) ->
     %% Todo should handle invalid unicode?
-    %% print above the prompt if we have a prompt.
-    %% otherwise print on the current line.
-    case {State#state.lines_before,{State#state.buffer_before, State#state.buffer_after}, State#state.lines_after} of
-        {[],{[],[]},[]} ->
-            {PutBuffer, _} = insert_buf(State, Binary),
-            {[encode(PutBuffer, U)], State};
-        _ ->
-            {Delete, DeletedState} = handle_request(State, delete_line),
-            {PutBuffer, _} = insert_buf(DeletedState, Binary),
-            {Redraw, _} = handle_request(State, redraw_prompt_pre_deleted),
-            {[Delete, encode(PutBuffer, U), Redraw], State}
-    end;
+    {PutBuffer, _} = insert_buf(State, Binary),
+    {[encode(PutBuffer, U)], State};
 handle_request(State = #state{}, delete_after_cursor) ->
     {[State#state.delete_after_cursor],
      State#state{buffer_after = [],
diff --git a/lib/kernel/test/interactive_shell_SUITE.erl b/lib/kernel/test/interactive_shell_SUITE.erl
index c3a685622b7e..30ef9afa6d27 100644
--- a/lib/kernel/test/interactive_shell_SUITE.erl
+++ b/lib/kernel/test/interactive_shell_SUITE.erl
@@ -976,6 +976,7 @@ shell_huge_input(Config) ->
     after
         stop_tty(Term)
     end.
+
 shell_receive_standard_out(Config) ->
     Term = start_tty(Config),
     try
@@ -987,7 +988,19 @@ shell_receive_standard_out(Config) ->
         ok
     after
         stop_tty(Term)
+    end,
+    Term2 = start_tty([{args,["-stdlib","shell_bgmsg_location","below"]}|Config]),
+    try
+        send_tty(Term2,"my_fun(5) -> ok; my_fun(N) -> receive after 100 -> io:format(\"~p\\n\", [N]), my_fun(N+1) end.\n"),
+        send_tty(Term2, "spawn(shell_default, my_fun, [0]). ABC\n"),
+        timer:sleep(1000),
+        check_location(Term2, {0,-18}), %% Check that we are at the same location relative to the start.
+        check_content(Term2, "..0\\s+1\\s+2\\s+3\\s+4"),
+        ok
+    after
+        stop_tty(Term2)
     end.
+
 %% Test that the shell works when invalid utf-8 (aka latin1) is sent to it
 shell_invalid_unicode(Config) ->
     Term = start_tty(Config),