feat(marks): restore viewport on jump #15831

** Refactor

Previously most functions used to "get" a mark returned a position,
changed the line number and sometimes changed even the current buffer.

Now functions return a {x}fmark_T making calling context aware whether
the mark is in another buffer without arcane casting. A new function is
provided for switching to the mark buffer and returning a flag style
Enum to convey what happen in the movement. If the cursor changed, line,
columns, if it changed buffer, etc.

The function to get named mark was split into multiple functions.

- mark_get() -> fmark_T
- mark_get_global() -> xfmark_T
- mark_get_local() -> fmark_T
  - mark_get_motion() -> fmark_T
  - mark_get_visual() -> fmark_T

Functions that manage the changelist and jumplist were also modified to
return mark types.

- get_jumplist -> fmark_T
- get_changelist -> fmark_T

The refactor is also seen mainly on normal.c, where all the mark
movement has been siphoned through one function nv_gomark, while the
other functions handle getting the mark and setting their movement
flags. To handle whether context marks should be left, etc.

** Mark View

While doing the refactor the concept of a mark view was also
implemented:

The view of a mark currently implemented as the number of lines between
the mark position on creation and the window topline. This allows for
moving not only back to the position of a mark but having the window
look similar to when the mark was defined. This is done by carrying and
extra element in the fmark_T struct, which can be extended later to also
restore horizontal shift.

*** User space features

1. There's a new option, jumpoptions+=view enables the mark view restoring
automatically when using the jumplist, changelist, alternate-file and
mark motions. <C-O> <C-I> g; g, <C-^> '[mark] `[mark]

** Limitations

- The view information is not saved in shada.
- Calls to get_mark should copy the value in the pointer since we are
  using pos_to_mark() to wrap and provide a homogeneous interfaces. This
  was also a limitation in the previous state of things.

1 files changed, 18 insertions, 19 deletions

diff --git a/src/nvim/api/buffer.c b/src/nvim/api/buffer.c
index 1504004c6c..806b649ce6 100644
--- a/src/nvim/api/buffer.c
+++ b/src/nvim/api/buffer.c
@@ -1156,17 +1156,17 @@ Boolean nvim_buf_del_mark(Buffer buffer, String name, Error *err)
     return res;
   }
 
-  pos_T *pos = getmark_buf(buf, *name.data, false);
+  fmark_T *fm = mark_get(buf, curwin, NULL, kMarkAllNoResolve, *name.data);
 
-  // pos point to NULL when there's no mark with name
-  if (pos == NULL) {
+  // fm is NULL when there's no mark with the given name
+  if (fm == NULL) {
     api_set_error(err, kErrorTypeValidation, "Invalid mark name: '%c'",
                   *name.data);
     return res;
   }
 
-  // pos->lnum is 0 when the mark is not valid in the buffer, or is not set.
-  if (pos->lnum != 0) {
+  // mark.lnum is 0 when the mark is not valid in the buffer, or is not set.
+  if (fm->mark.lnum != 0 && fm->fnum == buf->handle) {
     // since the mark belongs to the buffer delete it.
     res = set_mark(buf, name, 0, 0, err);
   }
@@ -1239,26 +1239,25 @@ ArrayOf(Integer, 2) nvim_buf_get_mark(Buffer buffer, String name, Error *err)
     return rv;
   }
 
-  pos_T *posp;
+  fmark_T *fm;
+  pos_T pos;
   char mark = *name.data;
 
-  try_start();
-  bufref_T save_buf;
-  switch_buffer(&save_buf, buf);
-  posp = getmark(mark, false);
-  restore_buffer(&save_buf);
-
-  if (try_end(err)) {
-    return rv;
-  }
-
-  if (posp == NULL) {
+  fm = mark_get(buf, curwin, NULL, kMarkAllNoResolve, mark);
+  if (fm == NULL) {
     api_set_error(err, kErrorTypeValidation, "Invalid mark name");
     return rv;
   }
+  // (0, 0) uppercase/file mark set in another buffer.
+  if (fm->fnum != buf->handle) {
+    pos.lnum = 0;
+    pos.col = 0;
+  } else {
+    pos = fm->mark;
+  }
 
-  ADD(rv, INTEGER_OBJ(posp->lnum));
-  ADD(rv, INTEGER_OBJ(posp->col));
+  ADD(rv, INTEGER_OBJ(pos.lnum));
+  ADD(rv, INTEGER_OBJ(pos.col));
 
   return rv;
 }