vim-patch:8.2.3141: no error when using :complete for :command without -nargs

Problem:    No error when using :complete for :command without -nargs.
Solution:   Give an error. (Martin Tournoij, closes vim/vim#8544, closes vim/vim#8541)
https://github.com/vim/vim/commit/de69a7353e9bec552e15dbe3706a9f4e88080fce

N/A patches for version.c:

vim-patch:8.1.1801: cannot build without the +eval feature

Problem:    Cannot build without the +eval feature.
Solution:   Always define funcexe_T.
https://github.com/vim/vim/commit/505e43a20eb25674b18d73971fe3b51dad917f9a

vim-patch:8.1.1818: unused variable

Problem:    Unused variable.
Solution:   Remove the variable. (Mike Williams)
https://github.com/vim/vim/commit/b4a88a0441a65a0c9411c294825a08ca703f541e

vim-patch:8.2.1464: Vim9: build warning for unused variable

Problem:    Vim9: build warning for unused variable.
Solution:   Delete the variable declaration.
https://github.com/vim/vim/commit/829ac868b7615d73dbfb536f7fcd44fc7c5b7c1d

vim-patch:8.2.2639: build failure when fsync() is not available

Problem:    Build failure when fsync() is not available.
Solution:   Add #ifdef.
https://github.com/vim/vim/commit/5ea79a2599d35f75e1ae8a75d2711c754c4cb7c4

vim-patch:8.2.2814: Vim9: unused variable

Problem:    Vim9: unused variable. (John Marriott)
Solution:   Adjust #ifdef.
https://github.com/vim/vim/commit/b06b50dfa06e1cbefd634e2735e7cd5ddd5b911c

vim-patch:8.2.2947: build failure without the channel feature

Problem:    Build failure without the channel feature.
Solution:   Add back #ifdef. (John Marriott)
https://github.com/vim/vim/commit/f5bfa8faa7bbe025c10148d37e8b47217a430a3b

vim-patch:8.2.2976: build failure without the +eval feature

Problem:    Build failure without the +eval feature.
Solution:   Add #ifdefs.
https://github.com/vim/vim/commit/8de901e1f1b051e02a61ae76ad7c925e4c0642e5

vim-patch:8.2.2986: build failure without the profile feature

Problem:    Build failure without the profile feature.
Solution:   Add #ifdef.
https://github.com/vim/vim/commit/d9f31c13d217b4b97f724774a67a6d1f8640e8ae

vim-patch:8.2.3114: Amiga-like systems: build error using stat()

Problem:    Amiga-like systems: build error using stat().
Solution:   Only build swapfile_process_running() on systems where it is
            actually used. (Ola Söder, closes vim/vim#8519)
https://github.com/vim/vim/commit/599a6e5b3629d943a795cd69e4d3d19886f86405

2 files changed, 30 insertions, 19 deletions

diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index d10ecf5c7f..3afcd9ec5a 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -5514,6 +5514,9 @@ invalid_count:
   return OK;
 }
 
+static char e_complete_used_without_nargs[] = N_(
+    "E1208: -complete used without -nargs");
+
 /*
  * ":command ..."
  */
@@ -5565,10 +5568,10 @@ static void ex_command(exarg_T *eap)
     uc_list(name, end - name);
   } else if (!ASCII_ISUPPER(*name)) {
     EMSG(_("E183: User defined commands must start with an uppercase letter"));
-    return;
   } else if (name_len <= 4 && STRNCMP(name, "Next", name_len) == 0) {
     EMSG(_("E841: Reserved name, cannot be used for user defined command"));
-    return;
+  } else if (compl > 0 && (argt & EX_EXTRA) == 0) {
+    EMSG(_(e_complete_used_without_nargs));
   } else {
     uc_add_command(name, end - name, p, argt, def, flags, compl, compl_arg,
                    addr_type_arg, eap->forceit);
diff --git a/src/nvim/testdir/test_usercommands.vim b/src/nvim/testdir/test_usercommands.vim
index 4621207d19..29e578ac6d 100644
--- a/src/nvim/testdir/test_usercommands.vim
+++ b/src/nvim/testdir/test_usercommands.vim
@@ -238,6 +238,8 @@ func Test_CmdErrors()
   call assert_fails('com! -complete=custom DoCmd :', 'E467:')
   call assert_fails('com! -complete=customlist DoCmd :', 'E467:')
   call assert_fails('com! -complete=behave,CustomComplete DoCmd :', 'E468:')
+  call assert_fails('com! -complete=file DoCmd :', 'E1208:')
+  call assert_fails('com! -nargs=0 -complete=file DoCmd :', 'E1208:')
   call assert_fails('com! -nargs=x DoCmd :', 'E176:')
   call assert_fails('com! -count=1 -count=2 DoCmd :', 'E177:')
   call assert_fails('com! -count=x DoCmd :', 'E178:')
@@ -306,27 +308,33 @@ func Test_CmdCompletion()
   call feedkeys(":com DoC\<C-A>\<C-B>\"\<CR>", 'tx')
   call assert_equal('"com DoC', @:)
 
-  com! -complete=behave DoCmd :
+  com! -nargs=1 -complete=behave DoCmd :
   call feedkeys(":DoCmd \<C-A>\<C-B>\"\<CR>", 'tx')
   call assert_equal('"DoCmd mswin xterm', @:)
 
-  " This does not work. Why?
-  "call feedkeys(":DoCmd x\<C-A>\<C-B>\"\<CR>", 'tx')
-  "call assert_equal('"DoCmd xterm', @:)
-
-  com! -complete=custom,CustomComplete DoCmd :
+  com! -nargs=* -complete=custom,CustomComplete DoCmd :
   call feedkeys(":DoCmd \<C-A>\<C-B>\"\<CR>", 'tx')
   call assert_equal('"DoCmd January February Mars', @:)
 
-  com! -complete=customlist,CustomCompleteList DoCmd :
+  com! -nargs=? -complete=customlist,CustomCompleteList DoCmd :
   call feedkeys(":DoCmd \<C-A>\<C-B>\"\<CR>", 'tx')
   call assert_equal('"DoCmd Monday Tuesday Wednesday', @:)
 
-  com! -complete=custom,CustomCompleteList DoCmd :
+  com! -nargs=+ -complete=custom,CustomCompleteList DoCmd :
   call assert_fails("call feedkeys(':DoCmd \<C-D>', 'tx')", 'E730:')
 
-  com! -complete=customlist,CustomComp DoCmd :
+  com! -nargs=+ -complete=customlist,CustomComp DoCmd :
   call assert_fails("call feedkeys(':DoCmd \<C-D>', 'tx')", 'E117:')
+
+  " custom completion without a function
+  com! -nargs=? -complete=custom, DoCmd
+  call assert_beeps("call feedkeys(':DoCmd \t', 'tx')")
+
+  " custom completion failure with the wrong function
+  com! -nargs=? -complete=custom,min DoCmd
+  call assert_fails("call feedkeys(':DoCmd \t', 'tx')", 'E118:')
+
+  delcom DoCmd
 endfunc
 
 func CallExecute(A, L, P)
@@ -459,21 +467,21 @@ func Test_command_list()
         \           execute('command DoCmd'))
 
   " Test with various -complete= argument values (non-exhaustive list)
-  command! -complete=arglist DoCmd :
+  command! -nargs=1 -complete=arglist DoCmd :
   call assert_equal("\n    Name              Args Address Complete    Definition"
-        \        .. "\n    DoCmd             0            arglist     :",
+        \        .. "\n    DoCmd             1            arglist     :",
         \           execute('command DoCmd'))
-  command! -complete=augroup DoCmd :
+  command! -nargs=* -complete=augroup DoCmd :
   call assert_equal("\n    Name              Args Address Complete    Definition"
-        \        .. "\n    DoCmd             0            augroup     :",
+        \        .. "\n    DoCmd             *            augroup     :",
         \           execute('command DoCmd'))
-  command! -complete=custom,CustomComplete DoCmd :
+  command! -nargs=? -complete=custom,CustomComplete DoCmd :
   call assert_equal("\n    Name              Args Address Complete    Definition"
-        \        .. "\n    DoCmd             0            custom      :",
+        \        .. "\n    DoCmd             ?            custom      :",
         \           execute('command DoCmd'))
-  command! -complete=customlist,CustomComplete DoCmd :
+  command! -nargs=+ -complete=customlist,CustomComplete DoCmd :
   call assert_equal("\n    Name              Args Address Complete    Definition"
-        \        .. "\n    DoCmd             0            customlist  :",
+        \        .. "\n    DoCmd             +            customlist  :",
         \           execute('command DoCmd'))
 
   " Test with various -narg= argument values.