fix(lua): on_yank error with blockwise multibyte region #20162

Prevent out of range error when calling `str_byteindex`.
Use `vim.str_byteindex(bufline, #bufline)` to cacluate utf length of `bufline`.
fix #20161

runtime/lua/vim/_editor.lua

@@ -416,11 +416,16 @@ function vim.region(bufnr, pos1, pos2, regtype, inclusive)
       c2 = c1 + regtype:sub(2)
       -- and adjust for non-ASCII characters
       bufline = vim.api.nvim_buf_get_lines(bufnr, l, l + 1, true)[1]
-      if c1 < #bufline then
+      local utflen = vim.str_utfindex(bufline, #bufline)
+      if c1 <= utflen then
         c1 = vim.str_byteindex(bufline, c1)
+      else
+        c1 = #bufline + 1
       end
-      if c2 < #bufline then
+      if c2 <= utflen then
         c2 = vim.str_byteindex(bufline, c2)
+      else
+        c2 = #bufline + 1
       end
     else
       c1 = (l == pos1[1]) and pos1[2] or 0

test/functional/lua/vim_spec.lua

@@ -2227,13 +2227,19 @@ describe('lua stdlib', function()
     eq(true, exec_lua[[return vim.g.test]])
   end)
 
-  it('vim.region', function()
-    insert(helpers.dedent( [[
-    text tααt tααt text
-    text tαxt txtα tex
-    text tαxt tαxt
-    ]]))
-    eq({5,15}, exec_lua[[ return vim.region(0,{1,5},{1,14},'v',true)[1] ]])
+  describe('vim.region', function()
+    it('charwise', function()
+      insert(helpers.dedent( [[
+      text tααt tααt text
+      text tαxt txtα tex
+      text tαxt tαxt
+      ]]))
+      eq({5,15}, exec_lua[[ return vim.region(0,{1,5},{1,14},'v',true)[1] ]])
+    end)
+    it('blockwise', function()
+      insert([[αα]])
+      eq({0,5}, exec_lua[[ return vim.region(0,{0,0},{0,4},'3',true)[0] ]])
+    end)
   end)
 
   describe('vim.on_key', function()