perf(hightlight): compute only bounds for non-blockwise highlights

Problem:
vim.hl.range() computes a segment for every selected line, then discards
all but the outer endpoints for characterwise and linewise highlights.
This makes highlighting large yanks and puts unnecessarily expensive.

Solution:
Use getregionpos() with bounds=true for these highlights. Also use bounds
in the keymap example that only needs the first and last selected lines.

AI-assisted

2 files changed, 6 insertions, 5 deletions

diff --git a/runtime/lua/vim/hl.lua b/runtime/lua/vim/hl.lua
index 552285c7da..c02986b28e 100644
--- a/runtime/lua/vim/hl.lua
+++ b/runtime/lua/vim/hl.lua
@@ -94,15 +94,15 @@ function M.range(buf, ns, hlgroup, start, finish, opts)
     end
   end)
 
+  -- For non-blockwise selection, use a single extmark and only compute its bounds.
+  local bounds = regtype == 'v' or regtype == 'V'
   local region = vim.fn.getregionpos(pos1, pos2, {
     type = regtype,
     exclusive = not inclusive,
     eol = true,
+    bounds = bounds,
   })
-  -- For non-blockwise selection, use a single extmark.
-  if regtype == 'v' or regtype == 'V' then
-    --- @type [ [integer, integer, integer, integer], [integer, integer, integer, integer]][]
-    region = { { assert(region[1])[1], assert(region[#region])[2] } }
+  if bounds then
     local region1 = assert(region[1])
     if
       regtype == 'V'
diff --git a/runtime/lua/vim/keymap.lua b/runtime/lua/vim/keymap.lua
index 7451f42ad4..061d3340fe 100644
--- a/runtime/lua/vim/keymap.lua
+++ b/runtime/lua/vim/keymap.lua
@@ -39,9 +39,10 @@ local keymap = {}
 ---     type = 'v',
 ---     exclusive = false,
 ---     eol = false,
+---     bounds = true,
 ---   })
 ---   local line1 = region[1][1][2]
----   local line2 = region[#region][1][2]
+---   local line2 = region[1][2][2]
 ---   vim.print({ line1, line2 })
 --- end)
 ---