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, 115 insertions, 0 deletions

diff --git a/test/functional/editor/jump_spec.lua b/test/functional/editor/jump_spec.lua
index d09c20f226..d3d3d7f79d 100644
--- a/test/functional/editor/jump_spec.lua
+++ b/test/functional/editor/jump_spec.lua
@@ -1,4 +1,5 @@
 local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
 
 local clear = helpers.clear
 local command = helpers.command
@@ -7,6 +8,7 @@ local funcs = helpers.funcs
 local feed = helpers.feed
 local exec_capture = helpers.exec_capture
 local write_file = helpers.write_file
+local curbufmeths = helpers.curbufmeths
 
 describe('jumplist', function()
   local fname1 = 'Xtest-functional-normal-jump'
@@ -137,3 +139,116 @@ describe("jumpoptions=stack behaves like 'tagstack'", function()
        exec_capture('jumps'))
   end)
 end)
+
+describe("jumpoptions=view", function()
+  local file1 = 'Xtestfile-functional-editor-jumps'
+  local file2 = 'Xtestfile-functional-editor-jumps-2'
+  local function content()
+    local c = {}
+    for i=1,30 do
+      c[i] = i .. " line"
+    end
+    return table.concat(c, "\n")
+  end
+  before_each(function()
+    clear()
+    write_file(file1, content(), false, false)
+    write_file(file2, content(), false, false)
+    command('set jumpoptions=view')
+  end)
+  after_each(function()
+    os.remove(file1)
+    os.remove(file2)
+  end)
+
+  it('restores the view', function()
+    local screen = Screen.new(5, 8)
+    screen:attach()
+    command("edit " .. file1)
+    feed("12Gztj")
+    feed("gg<C-o>")
+    screen:expect([[
+    12 line     |
+    ^13 line     |
+    14 line     |
+    15 line     |
+    16 line     |
+    17 line     |
+    18 line     |
+                |
+    ]])
+  end)
+
+  it('restores the view across files', function()
+    local screen = Screen.new(5, 5)
+    screen:attach()
+    command("args " .. file1 .. " " .. file2)
+    feed("12Gzt")
+    command("next")
+    feed("G")
+    screen:expect([[
+    27 line     |
+    28 line     |
+    29 line     |
+    ^30 line     |
+                |
+    ]])
+    feed("<C-o><C-o>")
+    screen:expect([[
+    ^12 line     |
+    13 line     |
+    14 line     |
+    15 line     |
+                |
+    ]])
+  end)
+
+  it('restores the view across files with <C-^>', function()
+    local screen = Screen.new(5, 5)
+    screen:attach()
+    command("args " .. file1 .. " " .. file2)
+    feed("12Gzt")
+    command("next")
+    feed("G")
+    screen:expect([[
+    27 line     |
+    28 line     |
+    29 line     |
+    ^30 line     |
+                |
+    ]])
+    feed("<C-^>")
+    screen:expect([[
+    ^12 line     |
+    13 line     |
+    14 line     |
+    15 line     |
+                |
+    ]])
+  end)
+
+  it('falls back to standard behavior when view can\'t be recovered', function()
+    local screen = Screen.new(5, 8)
+    screen:attach()
+    command("edit " .. file1)
+    feed("7GzbG")
+    curbufmeths.set_lines(0, 2, true, {})
+    -- Move to line 7, and set it as the last line visible on the view with zb, meaning to recover
+    -- the view it needs to put the cursor 7 lines from the top line. Then go to the end of the
+    -- file, delete 2 lines before line 7, meaning the jump/mark is moved 2 lines up to line 5.
+    -- Therefore when trying to jump back to it it's not possible to set a 7 line offset from the
+    -- mark position to the top line, since there's only 5 lines from the mark position to line 0.
+    -- Therefore falls back to standard behavior which is centering the view/line.
+    feed("<C-o>")
+    screen:expect([[
+    4 line      |
+    5 line      |
+    6 line      |
+    ^7 line      |
+    8 line      |
+    9 line      |
+    10 line     |
+                |
+    ]])
+  end)
+end)