feat(nvim_open_term): convert LF => CRLF (#26384)

Problem:
Unlike termopen(), nvim_open_term() PTYs do not carriage-return the
cursor on newline ("\n") input.

    nvim --clean
    :let chan_id = nvim_open_term(1, {})
    :call chansend(chan_id, ["here", "are", "some", "lines"])

Actual behavior:

    here
        are
           some
               lines

Expected behaviour:

    here
    are
    some
    lines

Solution:
Add `force_crlf` option, and enable it by default.

11 files changed, 91 insertions, 13 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 4aba1f8141..48bbdc33df 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -1231,6 +1231,8 @@ nvim_open_term({buffer}, {*opts})                           *nvim_open_term()*
                     is sent as a "\r", not as a "\n". |textlock| applies. It
                     is possible to call |nvim_chan_send()| directly in the
                     callback however. ["input", term, bufnr, data]
+                  • force_crlf: (boolean, default true) Convert "\n" to
+                    "\r\n".
 
     Return: ~
         Channel id, or 0 on error
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 04f143f0c3..9bfc577e87 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -344,6 +344,8 @@ The following changes to existing APIs or features add new behavior.
 • Diagnostic sign text is no longer configured with |sign_define()|.
   Use |vim.diagnostic.config()| instead.
 
+• Added "force_crlf" option field in |nvim_open_term()|.
+
 ==============================================================================
 REMOVED FEATURES                                                 *news-removed*
 
diff --git a/runtime/lua/vim/_meta/api.lua b/runtime/lua/vim/_meta/api.lua
index 4ad0a2e791..231e1c3404 100644
--- a/runtime/lua/vim/_meta/api.lua
+++ b/runtime/lua/vim/_meta/api.lua
@@ -1446,6 +1446,8 @@ function vim.api.nvim_notify(msg, log_level, opts) end
 ---                 is sent as a "\r", not as a "\n". `textlock` applies. It
 ---                 is possible to call `nvim_chan_send()` directly in the
 ---                 callback however. ["input", term, bufnr, data]
+---               • force_crlf: (boolean, default true) Convert "\n" to
+---                 "\r\n".
 --- @return integer
 function vim.api.nvim_open_term(buffer, opts) end
 
diff --git a/runtime/lua/vim/_meta/api_keysets.lua b/runtime/lua/vim/_meta/api_keysets.lua
index 6a3e574455..f64cdb8afd 100644
--- a/runtime/lua/vim/_meta/api_keysets.lua
+++ b/runtime/lua/vim/_meta/api_keysets.lua
@@ -217,6 +217,7 @@ error('Cannot require a meta file')
 
 --- @class vim.api.keyset.open_term
 --- @field on_input? function
+--- @field force_crlf? boolean
 
 --- @class vim.api.keyset.option
 --- @field scope? string
diff --git a/src/nvim/api/keysets_defs.h b/src/nvim/api/keysets_defs.h
index d1cbe43de0..c0daa0ca74 100644
--- a/src/nvim/api/keysets_defs.h
+++ b/src/nvim/api/keysets_defs.h
@@ -344,4 +344,5 @@ typedef struct {
 typedef struct {
   OptionalKeys is_set__open_term_;
   LuaRef on_input;
+  Boolean force_crlf;
 } Dict(open_term);
diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index a52d7493e3..2f3d527b9e 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -985,6 +985,7 @@ fail:
 ///            as a "\r", not as a "\n". |textlock| applies. It is possible
 ///            to call |nvim_chan_send()| directly in the callback however.
 ///                 ["input", term, bufnr, data]
+///          - force_crlf: (boolean, default true) Convert "\n" to "\r\n".
 /// @param[out] err Error details, if any
 /// @return Channel id, or 0 on error
 Integer nvim_open_term(Buffer buffer, Dict(open_term) *opts, Error *err)
@@ -1002,7 +1003,6 @@ Integer nvim_open_term(Buffer buffer, Dict(open_term) *opts, Error *err)
   }
 
   LuaRef cb = LUA_NOREF;
-
   if (HAS_KEY(opts, open_term, on_input)) {
     cb = opts->on_input;
     opts->on_input = LUA_NOREF;
@@ -1020,6 +1020,7 @@ Integer nvim_open_term(Buffer buffer, Dict(open_term) *opts, Error *err)
     .write_cb = term_write,
     .resize_cb = term_resize,
     .close_cb = term_close,
+    .force_crlf = GET_BOOL_OR_TRUE(opts, open_term, force_crlf),
   };
   channel_incref(chan);
   terminal_open(&chan->term, buf, topts);
diff --git a/src/nvim/channel.c b/src/nvim/channel.c
index ca8cbed8f9..fb4711f7d9 100644
--- a/src/nvim/channel.c
+++ b/src/nvim/channel.c
@@ -801,6 +801,7 @@ void channel_terminal_open(buf_T *buf, Channel *chan)
     .write_cb = term_write,
     .resize_cb = term_resize,
     .close_cb = term_close,
+    .force_crlf = false,
   };
   buf->b_p_channel = (OptInt)chan->id;  // 'channel' option
   channel_incref(chan);
diff --git a/src/nvim/terminal.c b/src/nvim/terminal.c
index af9693c4b0..3b70ee922a 100644
--- a/src/nvim/terminal.c
+++ b/src/nvim/terminal.c
@@ -43,6 +43,7 @@
 #include <vterm.h>
 #include <vterm_keycodes.h>
 
+#include "klib/kvec.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/ascii_defs.h"
@@ -80,6 +81,7 @@
 #include "nvim/optionstr.h"
 #include "nvim/pos_defs.h"
 #include "nvim/state.h"
+#include "nvim/strings.h"
 #include "nvim/terminal.h"
 #include "nvim/types_defs.h"
 #include "nvim/ui.h"
@@ -786,7 +788,21 @@ void terminal_receive(Terminal *term, const char *data, size_t len)
     return;
   }
 
-  vterm_input_write(term->vt, data, len);
+  if (term->opts.force_crlf) {
+    StringBuilder crlf_data = KV_INITIAL_VALUE;
+
+    for (size_t i = 0; i < len; i++) {
+      if (data[i] == '\n' && (i == 0 || (i > 0 && data[i - 1] != '\r'))) {
+        kv_push(crlf_data, '\r');
+      }
+      kv_push(crlf_data, data[i]);
+    }
+
+    vterm_input_write(term->vt, crlf_data.items, kv_size(crlf_data));
+    kv_destroy(crlf_data);
+  } else {
+    vterm_input_write(term->vt, data, len);
+  }
   vterm_screen_flush_damage(term->vts);
 }
 
diff --git a/src/nvim/terminal.h b/src/nvim/terminal.h
index db62bd2a5b..ffa97f17b2 100644
--- a/src/nvim/terminal.h
+++ b/src/nvim/terminal.h
@@ -16,6 +16,7 @@ typedef struct {
   terminal_write_cb write_cb;
   terminal_resize_cb resize_cb;
   terminal_close_cb close_cb;
+  bool force_crlf;
 } TerminalOptions;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
diff --git a/test/functional/terminal/channel_spec.lua b/test/functional/terminal/channel_spec.lua
index 6fb1a21561..b9abcd61c8 100644
--- a/test/functional/terminal/channel_spec.lua
+++ b/test/functional/terminal/channel_spec.lua
@@ -192,4 +192,55 @@ describe('no crash when TermOpen autocommand', function()
     ]]}
     assert_alive()
   end)
+
+  it('nvim_open_term({force_crlf=true}) converts newlines', function()
+    local buf = meths.create_buf(false, true)
+    local win = meths.get_current_win()
+    local term = meths.open_term(buf, {force_crlf = true})
+    screen:try_resize(8, 10)
+    meths.win_set_buf(win, buf)
+    meths.chan_send(term, 'here\nthere\nfoo\r\nbar\n\ntest')
+    screen:expect{grid=[[
+      ^here        |
+      there       |
+      foo         |
+      bar         |
+                  |
+      test        |
+      {0:~           }|
+      {0:~           }|
+      {0:~           }|
+                  |
+    ]]}
+    meths.chan_send(term, '\nfirst')
+    screen:expect{grid=[[
+      ^here        |
+      there       |
+      foo         |
+      bar         |
+                  |
+      test        |
+      first       |
+      {0:~           }|
+      {0:~           }|
+                  |
+    ]]}
+    meths.buf_delete(buf, {force = true})
+    buf = meths.create_buf(false, true)
+    term = meths.open_term(buf, {force_crlf = false})
+    meths.win_set_buf(win, buf)
+    meths.chan_send(term, 'here\nthere')
+    screen:expect{grid=[[
+      ^here        |
+          there   |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+    ]]}
+  end)
 end)
diff --git a/test/functional/terminal/scrollback_spec.lua b/test/functional/terminal/scrollback_spec.lua
index d2c636b03f..00104734ef 100644
--- a/test/functional/terminal/scrollback_spec.lua
+++ b/test/functional/terminal/scrollback_spec.lua
@@ -576,21 +576,21 @@ describe("pending scrollback line handling", function()
     ]]
     screen:expect [[
       {1:  1 }^a                         |
-      {1:  2 } a                        |
-      {1:  3 }  a                       |
-      {1:  4 }   a                      |
-      {1:  5 }    a                     |
-      {1:  6 }     a                    |
+      {1:  2 }a                         |
+      {1:  3 }a                         |
+      {1:  4 }a                         |
+      {1:  5 }a                         |
+      {1:  6 }a                         |
                                     |
     ]]
     feed('G')
     screen:expect [[
-      {1:  7 }      a                   |
-      {1:  8 }       a                  |
-      {1:  9 }        a                 |
-      {1: 10 }         a                |
-      {1: 11 }          a               |
-      {1: 12 }           ^a              |
+      {1:  7 }a                         |
+      {1:  8 }a                         |
+      {1:  9 }a                         |
+      {1: 10 }a                         |
+      {1: 11 }a                         |
+      {1: 12 }^a                         |
                                     |
     ]]
     assert_alive()