paste: support replace mode (#11945)

* paste: support replace mode
* Clean up

Co-authored-by: Jesse Bakker <git@jessebakker.com>

src/nvim/lua/vim.lua

@@ -212,6 +212,18 @@ do
         vim.api.nvim_put(lines, 'c', true, true)
         -- XXX: Normal-mode: workaround bad cursor-placement after first chunk.
         vim.api.nvim_command('normal! a')
+      elseif phase < 2 and mode == 'R' then
+        local nchars = 0
+        for _, line in ipairs(lines) do
+            nchars = nchars + line:len()
+        end
+        local row, col = unpack(vim.api.nvim_win_get_cursor(0))
+        local bufline = vim.api.nvim_buf_get_lines(0, row-1, row, true)[1]
+        local firstline = lines[1]
+        firstline = bufline:sub(1, col)..firstline
+        lines[1] = firstline
+        lines[#lines] = lines[#lines]..bufline:sub(col + nchars + 1, bufline:len())
+        vim.api.nvim_buf_set_lines(0, row-1, row, false, lines)
       else
         vim.api.nvim_put(lines, 'c', false, true)
       end

test/functional/api/vim_spec.lua

@@ -571,6 +571,28 @@ describe('API', function()
       eq({0,7,1,0}, funcs.getpos('.'))
       eq(false, nvim('get_option', 'paste'))
     end)
+    it('Replace-mode', function()
+      -- Within single line
+      nvim('put', {'aabbccdd', 'eeffgghh', 'iijjkkll'}, "c", true, false)
+      command('normal l')
+      command('startreplace')
+      nvim('paste', '123456', true, -1)
+      expect([[
+      a123456d
+      eeffgghh
+      iijjkkll]])
+      command('%delete _')
+      -- Across lines
+      nvim('put', {'aabbccdd', 'eeffgghh', 'iijjkkll'}, "c", true, false)
+      command('normal l')
+      command('startreplace')
+      nvim('paste', '123\n456', true, -1)
+      expect([[
+      a123
+      456d
+      eeffgghh
+      iijjkkll]])
+    end)
     it('crlf=false does not break lines at CR, CRLF', function()
       nvim('paste', 'line 1\r\n\r\rline 2\nline 3\rline 4\r', false, -1)
       expect('line 1\r\n\r\rline 2\nline 3\rline 4\r')