feat(marks): virtual lines support horizontal scrolling (#32497)

Add a new field `virt_lines_overflow` that enables horizontal scrolling
for virtual lines when set to "scroll".

4 files changed, 17 insertions, 3 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index d3d18e9d6b..ec3dfebbc0 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -2651,6 +2651,12 @@ nvim_buf_set_extmark({buffer}, {ns_id}, {line}, {col}, {opts})
                   • virt_lines_above: place virtual lines above instead.
                   • virt_lines_leftcol: Place virtual lines in the leftmost
                     column of the window, bypassing sign and number columns.
+                  • virt_lines_overflow: controls how to handle virtual lines
+                    wider than the window. Currently takes the one of the
+                    following values:
+                    • "trunc": truncate virtual lines on the right (default).
+                    • "scroll": virtual lines can scroll horizontally with
+                      'nowrap', otherwise the same as "trunc".
                   • ephemeral : for use with |nvim_set_decoration_provider()|
                     callbacks. The mark will only be used for the current
                     redraw cycle, and not be permantently stored in the
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index da672f449c..f743bfc78b 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -202,9 +202,12 @@ API
 • |nvim_echo()| `err` field to print error messages and `chunks` accepts
   highlight group IDs.
 • |nvim_open_win()| `relative` field can be set to "laststatus" and "tabline".
-• |nvim_buf_set_extmark()| `hl_group` field can be an array of layered groups
+• |nvim_buf_set_extmark()| new field `virt_lines_overflow` accepts value `scroll` to
+  enable horizontal scrolling for virtual lines with 'nowrap'.
+  right aligned text that truncates before covering up buffer text.
+• |nvim_buf_set_extmark()| `hl_group` field can be an array of layered groups.
 • |vim.hl.range()| now has a optional `timeout` field which allows for a timed highlight
-• |nvim_buf_set_extmark()| virt_text_pos accepts `eol_right_align` to
+• |nvim_buf_set_extmark()| `virt_text_pos` field accepts value `eol_right_align` to
   allow for right aligned text that truncates before covering up buffer text.
 
 DEFAULTS
diff --git a/runtime/lua/vim/_meta/api.lua b/runtime/lua/vim/_meta/api.lua
index 96ee376882..a6ffb43146 100644
--- a/runtime/lua/vim/_meta/api.lua
+++ b/runtime/lua/vim/_meta/api.lua
@@ -641,7 +641,11 @@ function vim.api.nvim_buf_line_count(buffer) end
 --- - virt_lines_leftcol: Place virtual lines in the leftmost
 ---                       column of the window, bypassing
 ---                       sign and number columns.
----
+--- - virt_lines_overflow: controls how to handle virtual lines wider
+---     than the window. Currently takes the one of the following values:
+---   - "trunc": truncate virtual lines on the right (default).
+---   - "scroll": virtual lines can scroll horizontally with 'nowrap',
+---      otherwise the same as "trunc".
 --- - ephemeral : for use with `nvim_set_decoration_provider()`
 ---     callbacks. The mark will only be used for the current
 ---     redraw cycle, and not be permantently stored in the
diff --git a/runtime/lua/vim/_meta/api_keysets.lua b/runtime/lua/vim/_meta/api_keysets.lua
index 4d0665872b..a66e373851 100644
--- a/runtime/lua/vim/_meta/api_keysets.lua
+++ b/runtime/lua/vim/_meta/api_keysets.lua
@@ -258,6 +258,7 @@ error('Cannot require a meta file')
 --- @field virt_lines? any[]
 --- @field virt_lines_above? boolean
 --- @field virt_lines_leftcol? boolean
+--- @field virt_lines_overflow? string
 --- @field strict? boolean
 --- @field sign_text? string
 --- @field sign_hl_group? integer|string