vim-patch:9.1.1408: not easily possible to complete from register content (#34198)

Problem:  not easily possible to complete from register content
Solution: add register-completion submode using i_CTRL-X_CTRL-R
          (glepnir)

closes: vim/vim#17354

0546068aae

test/functional/editor/completion_spec.lua

@@ -124,7 +124,7 @@ describe('completion', function()
         foo                                                         |
         ^                                                            |
         {1:~                                                           }|*5
-        {5:-- ^X mode (^]^D^E^F^I^K^L^N^O^Ps^U^V^Y)}                    |
+        {5:-- ^X mode (^]^D^E^F^I^K^L^N^O^P^Rs^U^V^Y)}                  |
       ]])
       feed('<C-n>')
       screen:expect([[

test/functional/ui/float_spec.lua

@@ -3519,7 +3519,7 @@ describe('float window', function()
                                                             |
           {0:~                                                 }|*7
         ## grid 3
-          {3:-- ^X mode (^]^D^E^F^I^K^L^N^O^Ps^U^V^Y)}          |
+          {3:-- ^X mode (^]^D^E^F^I^K^L^N^O^P^Rs^U^V^Y)}        |
         ## grid 4
           {1:   }|
           {2:~  }|*2
@@ -3543,7 +3543,7 @@ describe('float window', function()
           {1:   }  {1:^   }                                          |
           {2:~  }{0:  }{2:~  }{0:                                          }|*2
           {0:~                                                 }|*5
-          {3:-- ^X mode (^]^D^E^F^I^K^L^N^O^Ps^U^V^Y)}          |
+          {3:-- ^X mode (^]^D^E^F^I^K^L^N^O^P^Rs^U^V^Y)}        |
         ]],
         }
       end

test/functional/ui/messages_spec.lua

@@ -815,7 +815,7 @@ describe('ui/ext_messages', function()
       ^                         |
       {1:~                        }|*2
     ]],
-      showmode = { { '-- ^X mode (^]^D^E^F^I^K^L^N^O^Ps^U^V^Y)', 5, 11 } },
+      showmode = { { '-- ^X mode (^]^D^E^F^I^K^L^N^O^P^Rs^U^V^Y)', 5, 11 } },
     }
 
     feed('<c-p>')

test/old/testdir/test_ins_complete.vim

@@ -3792,4 +3792,85 @@ func Test_complete_match()
   delfunc TestComplete
 endfunc
 
+func Test_register_completion()
+  let @a = "completion test apple application"
+  let @b = "banana behavior better best"
+  let @c = "complete completion compliment computer"
+  let g:save_reg = ''
+  func GetItems()
+    let g:result = complete_info(['pum_visible'])
+  endfunc
+
+  new
+  call setline(1, "comp")
+  call cursor(1, 4)
+  call feedkeys("a\<C-X>\<C-R>\<C-N>\<C-N>\<Esc>", 'tx')
+  call assert_equal("compliment", getline(1))
+
+  inoremap <buffer><F2> <C-R>=GetItems()<CR>
+  call feedkeys("S\<C-X>\<C-R>\<F2>\<ESC>", 'tx')
+  call assert_equal(1, g:result['pum_visible'])
+
+  call setline(1, "app")
+  call cursor(1, 3)
+  call feedkeys("a\<C-X>\<C-R>\<C-N>\<Esc>", 'tx')
+  call assert_equal("application", getline(1))
+
+  " Test completion with case differences
+  set ignorecase
+  let @e = "TestCase UPPERCASE lowercase"
+  call setline(1, "testc")
+  call cursor(1, 5)
+  call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+  call assert_equal("TestCase", getline(1))
+
+  " Test clipboard registers if available
+  if has('clipboard_working')
+    let g:save_reg = getreg('*')
+    call setreg('*', "clipboard selection unique words")
+    call setline(1, "uni")
+    call cursor(1, 3)
+    call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+    call assert_equal("unique", getline(1))
+    call setreg('*', g:save_reg)
+
+    let g:save_reg = getreg('+')
+    call setreg('+', "system clipboard special content")
+    call setline(1, "spe")
+    call cursor(1, 3)
+    call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+    call assert_equal("special", getline(1))
+    call setreg('+', g:save_reg)
+
+    call setreg('*', g:save_reg)
+    call setreg('a', "normal register")
+    call setreg('*', "clipboard mixed content")
+    call setline(1, "mix")
+    call cursor(1, 3)
+    call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+    call assert_equal("mixed", getline(1))
+    call setreg('*', g:save_reg)
+  endif
+
+  " Test black hole register should be skipped
+  let @_ = "blackhole content should not appear"
+  call setline(1, "black")
+  call cursor(1, 5)
+  call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+  call assert_equal("black", getline(1))
+
+  let @1 = "recent yank zero"
+  call setline(1, "ze")
+  call cursor(1, 2)
+  call feedkeys("a\<C-X>\<C-R>\<Esc>", 'tx')
+  call assert_equal("zero", getline(1))
+
+  " Clean up
+  bwipe!
+  delfunc GetItems
+  unlet g:result
+  unlet g:save_reg
+  set ignorecase&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable