vim-patch:9.1.1539: completion: messages don't respect 'shm' setting (#34923)

Problem:  completion: messages don't respect 'shm' setting
Solution: Turn off completion messages when 'shortmess' includes "c"
          (Girish Palya).

`:set shortmess+=c` is intended to reduce noise during completion by
suppressing messages.
Previously, some completion messages still appeared regardless of this setting.

This change ensures that **all** completion-related messages are suppressed
when `'c'` is present in `'shortmess'`.

Not entirely sure if the original behavior was intentional. If there's a
reason certain messages were always shown, feel free to close this without
merging.

closes: vim/vim#17737

fe1d3c8af7

Co-authored-by: Girish Palya <girishji@gmail.com>

test/functional/editor/completion_spec.lua

@@ -1373,4 +1373,33 @@ describe('completion', function()
       {5:-- Keyword completion (^N^P) The only match}                 |
     ]])
   end)
+
+  -- oldtest: Test_shortmess()
+  it('shortmess+=c turns off completion messages', function()
+    command([[call setline(1, ['hello', 'hullo', 'heee'])]])
+    feed('Goh<C-N>')
+    screen:expect([[
+      hello                                                       |
+      hullo                                                       |
+      heee                                                        |
+      hello^                                                       |
+      {12:hello          }{1:                                             }|
+      {4:hullo          }{1:                                             }|
+      {4:heee           }{1:                                             }|
+      {5:-- Keyword completion (^N^P) }{6:match 1 of 3}                   |
+    ]])
+    feed('<Esc>')
+    command('set shm+=c')
+    feed('Sh<C-N>')
+    screen:expect([[
+      hello                                                       |
+      hullo                                                       |
+      heee                                                        |
+      hello^                                                       |
+      {12:hello          }{1:                                             }|
+      {4:hullo          }{1:                                             }|
+      {4:heee           }{1:                                             }|
+      {5:-- INSERT --}                                                |
+   ]])
+  end)
 end)

test/old/testdir/test_ins_complete.vim

@@ -5059,4 +5059,25 @@ func Test_nonkeyword_trigger()
   unlet g:CallCount
 endfunc
 
+" Test that option shortmess=c turns off completion messages
+func Test_shortmess()
+  CheckScreendump
+
+  let lines =<< trim END
+    call setline(1, ['hello', 'hullo', 'heee'])
+  END
+
+  call writefile(lines, 'Xpumscript', 'D')
+  let buf = RunVimInTerminal('-S Xpumscript', #{rows: 12})
+  call term_sendkeys(buf, "Goh\<C-N>")
+  call TermWait(buf, 200)
+  call VerifyScreenDump(buf, 'Test_shortmess_complmsg_1', {})
+  call term_sendkeys(buf, "\<ESC>:set shm+=c\<CR>")
+  call term_sendkeys(buf, "Sh\<C-N>")
+  call TermWait(buf, 200)
+  call VerifyScreenDump(buf, 'Test_shortmess_complmsg_2', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable