refactor(api): reduce temporary allocations when replacing lines

The way ml_replace_buf is implemented makes it unfriendly for
being used in a loop: every call allocates a scratch buffer for putting
the line into the "dirty" state. This then immediately needs to be freed
as the next ml_replace_buf and/or ml_append_buf call will flush that buffer.

It's better to later pay the price of allocating the scratch buffer only if
the line is being immediately edited (likely when using the API to only
change one line) with an extra memcpy, than allocating that buffer
multiple times every time the API is called.

Of course, a separate xmalloc/xfree cycle for each time the dirty line
changes is unwanted to begin with. But fixing that is a later refactor.

1 files changed, 9 insertions, 8 deletions

diff --git a/src/nvim/api/deprecated.c b/src/nvim/api/deprecated.c
index 9b8cacd7c2..f805c945f3 100644
--- a/src/nvim/api/deprecated.c
+++ b/src/nvim/api/deprecated.c
@@ -225,12 +225,12 @@ Dictionary nvim_get_hl_by_name(String name, Boolean rgb, Arena *arena, Error *er
 ///                   the end of the buffer.
 /// @param lines      Array of lines
 /// @param[out] err   Error details, if any
-void buffer_insert(Buffer buffer, Integer lnum, ArrayOf(String) lines, Error *err)
+void buffer_insert(Buffer buffer, Integer lnum, ArrayOf(String) lines, Arena *arena, Error *err)
   FUNC_API_DEPRECATED_SINCE(1)
 {
   // "lnum" will be the index of the line after inserting,
   // no matter if it is negative or not
-  nvim_buf_set_lines(0, buffer, lnum, lnum, true, lines, err);
+  nvim_buf_set_lines(0, buffer, lnum, lnum, true, lines, arena, err);
 }
 
 /// Gets a buffer line
@@ -272,13 +272,13 @@ String buffer_get_line(Buffer buffer, Integer index, Arena *arena, Error *err)
 /// @param index    Line index
 /// @param line     Contents of the new line
 /// @param[out] err Error details, if any
-void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
+void buffer_set_line(Buffer buffer, Integer index, String line, Arena *arena, Error *err)
   FUNC_API_DEPRECATED_SINCE(1)
 {
   Object l = STRING_OBJ(line);
   Array array = { .items = &l, .size = 1 };
   index = convert_index(index);
-  nvim_buf_set_lines(0, buffer, index, index + 1, true,  array, err);
+  nvim_buf_set_lines(0, buffer, index, index + 1, true,  array, arena, err);
 }
 
 /// Deletes a buffer line
@@ -291,12 +291,12 @@ void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
 /// @param buffer   buffer handle
 /// @param index    line index
 /// @param[out] err Error details, if any
-void buffer_del_line(Buffer buffer, Integer index, Error *err)
+void buffer_del_line(Buffer buffer, Integer index, Arena *arena, Error *err)
   FUNC_API_DEPRECATED_SINCE(1)
 {
   Array array = ARRAY_DICT_INIT;
   index = convert_index(index);
-  nvim_buf_set_lines(0, buffer, index, index + 1, true, array, err);
+  nvim_buf_set_lines(0, buffer, index, index + 1, true, array, arena, err);
 }
 
 /// Retrieves a line range from the buffer
@@ -342,12 +342,13 @@ ArrayOf(String) buffer_get_line_slice(Buffer buffer,
 //                        array will delete the line range)
 /// @param[out] err       Error details, if any
 void buffer_set_line_slice(Buffer buffer, Integer start, Integer end, Boolean include_start,
-                           Boolean include_end, ArrayOf(String) replacement, Error *err)
+                           Boolean include_end, ArrayOf(String) replacement, Arena *arena,
+                           Error *err)
   FUNC_API_DEPRECATED_SINCE(1)
 {
   start = convert_index(start) + !include_start;
   end = convert_index(end) + include_end;
-  nvim_buf_set_lines(0, buffer, start, end, false, replacement, err);
+  nvim_buf_set_lines(0, buffer, start, end, false, replacement, arena, err);
 }
 
 /// Sets a buffer-scoped (b:) variable