fix(api): validate command names in nvim_add_user_command (#17406)

This uses the same validation used when defining commands with
`:command`.

3 files changed, 50 insertions, 10 deletions

diff --git a/src/nvim/api/private/helpers.c b/src/nvim/api/private/helpers.c
index ddcfff0097..2b107a3f27 100644
--- a/src/nvim/api/private/helpers.c
+++ b/src/nvim/api/private/helpers.c
@@ -1384,6 +1384,11 @@ void add_user_command(String name, Object command, Dict(user_command) *opts, int
   LuaRef luaref = LUA_NOREF;
   LuaRef compl_luaref = LUA_NOREF;
 
+  if (!uc_validate_name(name.data)) {
+    api_set_error(err, kErrorTypeValidation, "Invalid command name");
+    goto err;
+  }
+
   if (mb_islower(name.data[0])) {
     api_set_error(err, kErrorTypeValidation, "'name' must begin with an uppercase letter");
     goto err;
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 4dba0b97ed..87f8865133 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -5164,6 +5164,24 @@ char_u *get_command_name(expand_T *xp, int idx)
   return cmdnames[idx].cmd_name;
 }
 
+/// Check for a valid user command name
+///
+/// If the given {name} is valid, then a pointer to the end of the valid name is returned.
+/// Otherwise, returns NULL.
+char *uc_validate_name(char *name)
+{
+  if (ASCII_ISALPHA(*name)) {
+    while (ASCII_ISALNUM(*name)) {
+      name++;
+    }
+  }
+  if (!ends_excmd(*name) && !ascii_iswhite(*name)) {
+    return NULL;
+  }
+
+  return name;
+}
+
 int uc_add_command(char_u *name, size_t name_len, char_u *rep, uint32_t argt, long def, int flags,
                    int compl, char_u *compl_arg, LuaRef compl_luaref, cmd_addr_T addr_type,
                    LuaRef luaref, bool force)
@@ -5679,23 +5697,18 @@ static void ex_command(exarg_T *eap)
 
   // Get the name (if any) and skip to the following argument.
   name = p;
-  if (ASCII_ISALPHA(*p)) {
-    while (ASCII_ISALNUM(*p)) {
-      p++;
-    }
-  }
-  if (!ends_excmd(*p) && !ascii_iswhite(*p)) {
+  end = (char_u *)uc_validate_name((char *)name);
+  if (!end) {
     emsg(_("E182: Invalid command name"));
     return;
   }
-  end = p;
-  name_len = (int)(end - name);
+  name_len = (size_t)(end - name);
 
   // If there is nothing after the name, and no attributes were specified,
   // we are listing commands
   p = skipwhite(end);
   if (!has_attr && ends_excmd(*p)) {
-    uc_list(name, end - name);
+    uc_list(name, name_len);
   } else if (!ASCII_ISUPPER(*name)) {
     emsg(_("E183: User defined commands must start with an uppercase letter"));
   } else if (name_len <= 4 && STRNCMP(name, "Next", name_len) == 0) {
@@ -5703,7 +5716,7 @@ static void ex_command(exarg_T *eap)
   } 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, LUA_NOREF,
+    uc_add_command(name, name_len, p, argt, def, flags, compl, compl_arg, LUA_NOREF,
                    addr_type_arg, LUA_NOREF, eap->forceit);
   }
 }
diff --git a/test/functional/api/command_spec.lua b/test/functional/api/command_spec.lua
index d64d324a88..de22c9078c 100644
--- a/test/functional/api/command_spec.lua
+++ b/test/functional/api/command_spec.lua
@@ -180,6 +180,28 @@ describe('nvim_add_user_command', function()
     feed('<C-U>Test b<Tab>')
     eq('Test bbb', funcs.getcmdline())
   end)
+
+  it('does not allow invalid command names', function()
+    matches("'name' must begin with an uppercase letter", pcall_err(exec_lua, [[
+      vim.api.nvim_add_user_command('test', 'echo "hi"', {})
+    ]]))
+
+    matches('Invalid command name', pcall_err(exec_lua, [[
+      vim.api.nvim_add_user_command('t@', 'echo "hi"', {})
+    ]]))
+
+    matches('Invalid command name', pcall_err(exec_lua, [[
+      vim.api.nvim_add_user_command('T@st', 'echo "hi"', {})
+    ]]))
+
+    matches('Invalid command name', pcall_err(exec_lua, [[
+      vim.api.nvim_add_user_command('Test!', 'echo "hi"', {})
+    ]]))
+
+    matches('Invalid command name', pcall_err(exec_lua, [[
+      vim.api.nvim_add_user_command('💩', 'echo "hi"', {})
+    ]]))
+  end)
 end)
 
 describe('nvim_del_user_command', function()