vim-patch:9.1.1518: getcompletiontype() may crash (#34819)

Problem:  getcompletiontype() crashes when no completion is available
          (after v9.1.1509).
Solution: Don't call set_expand_context() (zeertzjq)

fixes: vim/vim#17681
closes: vim/vim#17684

e2c0f81dd0

src/nvim/cmdexpand.c

@@ -3854,10 +3854,7 @@ void f_getcompletiontype(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 
   int cmdline_len = (int)strlen(pat);
   set_cmd_context(&xpc, (char *)pat, cmdline_len, cmdline_len, false);
-  xpc.xp_pattern_len = strlen(xpc.xp_pattern);
-  xpc.xp_col = cmdline_len;
-
-  rettv->vval.v_string = get_cmdline_completion(&xpc);
+  rettv->vval.v_string = cmdcomplete_type_to_str(xpc.xp_context, xpc.xp_arg);
 
   ExpandCleanup(&xpc);
 }

src/nvim/eval.lua

@@ -3760,8 +3760,8 @@ M.funcs = {
       |getcmdprompt()|, |getcmdcomplpat()| and |setcmdline()|.
       Returns an empty string when completion is not defined.
 
-      To get the type of the command-line completion for the
-      specified string, use |getcompletiontype()|.
+      To get the type of the command-line completion for a specified
+      string, use |getcompletiontype()|.
     ]=],
     name = 'getcmdcompltype',
     params = {},

src/nvim/ex_getln.c

@@ -4198,31 +4198,28 @@ static char *get_cmdline_completion_pattern(void)
 }
 
 /// Get the command-line completion type.
-char *get_cmdline_completion(expand_T *xpc)
+static char *get_cmdline_completion(void)
 {
-  int xp_context = xpc->xp_context;
+  if (cmdline_star > 0) {
+    return NULL;
+  }
+
+  CmdlineInfo *p = get_ccline_ptr();
+  if (p == NULL || p->xpc == NULL) {
+    return NULL;
+  }
+
+  int xp_context = p->xpc->xp_context;
   if (xp_context == EXPAND_NOTHING) {
-    set_expand_context(xpc);
-    xp_context = xpc->xp_context;
-    xpc->xp_context = EXPAND_NOTHING;
+    set_expand_context(p->xpc);
+    xp_context = p->xpc->xp_context;
+    p->xpc->xp_context = EXPAND_NOTHING;
   }
   if (xp_context == EXPAND_UNSUCCESSFUL) {
     return NULL;
   }
 
-  char *cmd_compl = get_user_cmd_complete(NULL, xp_context);
-  if (cmd_compl == NULL) {
-    return NULL;
-  }
-
-  if (xp_context == EXPAND_USER_LIST || xp_context == EXPAND_USER_DEFINED) {
-    size_t buflen = strlen(cmd_compl) + strlen(xpc->xp_arg) + 2;
-    char *buffer = xmalloc(buflen);
-    snprintf(buffer, buflen, "%s,%s", cmd_compl, xpc->xp_arg);
-    return buffer;
-  }
-
-  return xstrdup(cmd_compl);
+  return cmdcomplete_type_to_str(xp_context, p->xpc->xp_arg);
 }
 
 /// "getcmdcomplpat()" function
@@ -4236,14 +4233,7 @@ void f_getcmdcomplpat(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 void f_getcmdcompltype(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
 {
   rettv->v_type = VAR_STRING;
-  rettv->vval.v_string = NULL;
-
-  CmdlineInfo *p = get_ccline_ptr();
-  if (cmdline_star > 0 || p == NULL || p->xpc == NULL) {
-    return;
-  }
-
-  rettv->vval.v_string = get_cmdline_completion(p->xpc);
+  rettv->vval.v_string = get_cmdline_completion();
 }
 
 /// "getcmdline()" function

src/nvim/usercmd.c

@@ -403,7 +403,7 @@ char *get_user_cmd_nargs(expand_T *xp, int idx)
 
 static char *get_command_complete(int arg)
 {
-  if (arg >= (int)(ARRAY_SIZE(command_complete))) {
+  if (arg < 0 || arg >= (int)(ARRAY_SIZE(command_complete))) {
     return NULL;
   }
   return (char *)command_complete[arg];
@@ -422,6 +422,26 @@ char *get_user_cmd_complete(expand_T *xp, int idx)
   return cmd_compl;
 }
 
+/// Get the name of completion type "expand" as an allocated string.
+/// "compl_arg" is the function name for "custom" and "customlist" types.
+/// Returns NULL if no completion is available.
+char *cmdcomplete_type_to_str(int expand, const char *compl_arg)
+{
+  char *cmd_compl = get_command_complete(expand);
+  if (cmd_compl == NULL || expand == EXPAND_USER_LUA) {
+    return NULL;
+  }
+
+  if (expand == EXPAND_USER_LIST || expand == EXPAND_USER_DEFINED) {
+    size_t buflen = strlen(cmd_compl) + strlen(compl_arg) + 2;
+    char *buffer = xmalloc(buflen);
+    snprintf(buffer, buflen, "%s,%s", cmd_compl, compl_arg);
+    return buffer;
+  }
+
+  return xstrdup(cmd_compl);
+}
+
 int cmdcomplete_str_to_type(const char *complete_str)
 {
   if (strncmp(complete_str, "custom,", 7) == 0) {