extmarks: better linewise/charwise handling

spec/range_spec.lua

@@ -627,7 +627,7 @@ describe('Range', function()
       'the lazy dog',
     }, function()
       -- Construct a range over 'fox jumps'
-      local r = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, Pos.MAX_COL), 'V')
+      local r = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, 5), 'v')
       local extrange = r:save_to_extmark()
       assert.are.same({ 'fox', 'jumps' }, extrange:range():lines())
       -- change 'jumps' to 'leaps':
@@ -642,4 +642,29 @@ describe('Range', function()
       assert.are.same({ 'fox', 'leaps' }, extrange:range():lines())
     end)
   end)
+
+  it('can save linewise extmark', function()
+    withbuf({
+      'The quick brown',
+      'fox',
+      'jumps',
+      'over',
+      'the lazy dog',
+    }, function()
+      -- Construct a range over 'fox jumps'
+      local r = Range.new(Pos.new(nil, 2, 1), Pos.new(nil, 3, Pos.MAX_COL), 'V')
+      local extrange = r:save_to_extmark()
+      assert.are.same({ 'fox', 'jumps' }, extrange:range():lines())
+
+      local extmark = vim.api.nvim_buf_get_extmark_by_id(
+        extrange.bufnr,
+        vim.api.nvim_create_namespace 'u.range',
+        extrange.id,
+        { details = true }
+      )
+      local row0, col0, details = unpack(extmark)
+      assert.are.same({ 1, 0 }, { row0, col0 })
+      assert.are.same({ 3, 0 }, { details.end_row, details.end_col })
+    end)
+  end)
 end)