vim-patch:9.0.1774: no support for custom cmdline completion (#24808)

Problem:  no support for custom cmdline completion
Solution: Add new vimscript functions

Add the following two functions:
- getcmdcompltype() returns custom and customlist functions

- getcompletion() supports both custom and customlist

closes: vim/vim#12228

https://github.com/vim/vim/commit/92997dda789ad8061841128cbc99b15ec0374411

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

4 files changed, 43 insertions, 4 deletions

diff --git a/src/nvim/cmdexpand.c b/src/nvim/cmdexpand.c
index eb9394c8ff..9470f77ab5 100644
--- a/src/nvim/cmdexpand.c
+++ b/src/nvim/cmdexpand.c
@@ -3515,12 +3515,34 @@ void f_getcompletion(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   ExpandInit(&xpc);
   xpc.xp_pattern = (char *)pattern;
   xpc.xp_pattern_len = strlen(xpc.xp_pattern);
+  xpc.xp_line = (char *)pattern;
+
   xpc.xp_context = cmdcomplete_str_to_type(type);
   if (xpc.xp_context == EXPAND_NOTHING) {
     semsg(_(e_invarg2), type);
     return;
   }
 
+  if (xpc.xp_context == EXPAND_USER_DEFINED) {
+    // Must be "custom,funcname" pattern
+    if (strncmp(type, "custom,", 7) != 0) {
+      semsg(_(e_invarg2), type);
+      return;
+    }
+
+    xpc.xp_arg = (char *)(type + 7);
+  }
+
+  if (xpc.xp_context == EXPAND_USER_LIST) {
+    // Must be "customlist,funcname" pattern
+    if (strncmp(type, "customlist,", 11) != 0) {
+      semsg(_(e_invarg2), type);
+      return;
+    }
+
+    xpc.xp_arg = (char *)(type + 11);
+  }
+
   if (xpc.xp_context == EXPAND_MENUS) {
     set_context_in_menu_cmd(&xpc, "menu", xpc.xp_pattern, false);
     xpc.xp_pattern_len = strlen(xpc.xp_pattern);
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index 154023b25f..be87201bbf 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -3582,7 +3582,9 @@ M.funcs = {
       color		color schemes
       command		Ex command
       compiler	compilers
-      diff_buffer     |:diffget| and |:diffput| completion
+      custom,{func}	custom completion, defined via {func}
+      customlist,{func} custom completion, defined via {func}
+      diff_buffer	|:diffget| and |:diffput| completion
       dir		directory names
       environment	environment variable names
       event		autocommand events
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 17c17e60ce..89f5e92c33 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -4165,11 +4165,19 @@ static char *get_cmdline_completion(void)
   }
 
   char *cmd_compl = get_user_cmd_complete(p->xpc, p->xpc->xp_context);
-  if (cmd_compl != NULL) {
-    return xstrdup(cmd_compl);
+  if (cmd_compl == NULL) {
+    return NULL;
   }
 
-  return NULL;
+  if (p->xpc->xp_context == EXPAND_USER_LIST
+      || p->xpc->xp_context == EXPAND_USER_DEFINED) {
+    size_t buflen = strlen(cmd_compl) + strlen(p->xpc->xp_arg) + 2;
+    char *buffer = xmalloc(buflen);
+    snprintf(buffer, buflen, "%s,%s", cmd_compl, p->xpc->xp_arg);
+    return buffer;
+  }
+
+  return xstrdup(cmd_compl);
 }
 
 /// "getcmdcompltype()" function
diff --git a/src/nvim/usercmd.c b/src/nvim/usercmd.c
index 65720342ce..e585818e75 100644
--- a/src/nvim/usercmd.c
+++ b/src/nvim/usercmd.c
@@ -425,6 +425,13 @@ char *get_user_cmd_complete(expand_T *xp, int idx)
 
 int cmdcomplete_str_to_type(const char *complete_str)
 {
+  if (strncmp(complete_str, "custom,", 7) == 0) {
+    return EXPAND_USER_DEFINED;
+  }
+  if (strncmp(complete_str, "customlist,", 11) == 0) {
+    return EXPAND_USER_LIST;
+  }
+
   for (int i = 0; i < (int)(ARRAY_SIZE(command_complete)); i++) {
     char *cmd_compl = get_command_complete(i);
     if (cmd_compl == NULL) {