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.

3 files changed, 11 insertions, 0 deletions

diff --git a/runtime/doc/motion.txt b/runtime/doc/motion.txt
index 228d1fcb87..9655d07a84 100644
--- a/runtime/doc/motion.txt
+++ b/runtime/doc/motion.txt
@@ -735,6 +735,11 @@ Jumping to a mark can be done in two ways:
 2. With ' (single quote): The cursor is positioned on the first non-blank
 			  character in the line of the specified location and
 			  the motion is linewise.
+						*mark-view*
+3. Apart from the above if 'jumpoptions' contains "view", they will also try to
+restore the mark view. This is the number of lines between the cursor position
+and the window topline (first buffer line displayed in the window) when it was
+set.
 
 						*m* *mark* *Mark*
 m{a-zA-Z}		Set mark {a-zA-Z} at cursor position (does not move
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 30ceb4f18b..eb377697e9 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3531,6 +3531,10 @@ A jump table for the options with a short description can be found at |Q_op|.
 			jumplist and then jumping to a location.
 			|jumplist-stack|
 
+	  view          When moving through the jumplist, |changelist|,
+			|alternate-file| or using |mark-motions| try to
+			restore the |mark-view| in which the action occurred.
+
 			*'joinspaces'* *'js'* *'nojoinspaces'* *'nojs'*
 'joinspaces' 'js'	boolean	(default off)
 			global
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 385a5f8f61..4b26e5501c 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -383,6 +383,8 @@ Normal commands:
 Options:
   'ttimeout', 'ttimeoutlen' behavior was simplified
   |jumpoptions| "stack" behavior
+  |jumpoptions| "view" tries to restore the |mark-view| when moving through
+  the |jumplist|, |changelist|, |alternate-file| or using |mark-motions|.
   'shortmess' the "F" flag does not affect output from autocommands
 
 Shell: