Don't show entire context when completing

src/nvim/lua/executor.c

@@ -1292,7 +1292,7 @@ static void nlua_add_treesitter(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
   lua_setfield(lstate, -2, "_ts_parse_query");
 }
 
-int nlua_expand_pat(char_u *pat, int *num_results, char_u ***results)
+int nlua_expand_pat(expand_T *xp, char_u *pat, int *num_results, char_u ***results)
 {
   lua_State *const lstate = nlua_enter();
   int ret = OK;
@@ -1307,10 +1307,11 @@ int nlua_expand_pat(char_u *pat, int *num_results, char_u ***results)
   // [ vim, vim._log_keystroke, buf ]
   lua_pushlstring(lstate, (const char *)pat, STRLEN(pat));
 
-  if (lua_pcall(lstate, 1, 1, 0)) {
+  if (lua_pcall(lstate, 1, 2, 0) != 0) {
     nlua_error(
         lstate,
         _("Error executing vim._expand_pat: %.*s"));
+    return FAIL;
   }
 
   Error err = ERROR_INIT;
@@ -1318,12 +1319,18 @@ int nlua_expand_pat(char_u *pat, int *num_results, char_u ***results)
   *num_results = 0;
   *results = NULL;
 
-  Array completions = nlua_pop_Array(lstate, &err);
+  int prefix_len = (int)nlua_pop_Integer(lstate, &err);
   if (ERROR_SET(&err)) {
     ret = FAIL;
     goto cleanup;
   }
 
+  Array completions = nlua_pop_Array(lstate, &err);
+  if (ERROR_SET(&err)) {
+    ret = FAIL;
+    goto cleanup_array;
+  }
+
   garray_T result_array;
   ga_init(&result_array, (int)sizeof(char *), 80);
   for (size_t i = 0; i < completions.size; i++) {
@@ -1331,7 +1338,7 @@ int nlua_expand_pat(char_u *pat, int *num_results, char_u ***results)
 
     if (v.type != kObjectTypeString) {
       ret = FAIL;
-      goto cleanup;
+      goto cleanup_array;
     }
 
     GA_APPEND(
@@ -1340,12 +1347,15 @@ int nlua_expand_pat(char_u *pat, int *num_results, char_u ***results)
         vim_strsave((char_u *)v.data.string.data));
   }
 
+  xp->xp_pattern += prefix_len;
   *results = result_array.ga_data;
   *num_results = result_array.ga_len;
 
-cleanup:
+cleanup_array:
   api_free_array(completions);
 
+cleanup:
+
   if (ret == FAIL) {
     ga_clear(&result_array);
   }

src/nvim/lua/vim.lua

@@ -547,7 +547,7 @@ function vim._expand_pat(pat, env)
   if pat == '' then
     local result = vim.tbl_keys(env)
     table.sort(result)
-    return result
+    return result, 0
   end
 
   -- TODO: We can handle spaces in [] ONLY.
@@ -558,7 +558,7 @@ function vim._expand_pat(pat, env)
 
   -- Get the last part of the pattern
   local last_part = pat:match("[%w.:_%[%]'\"]+$")
-  if not last_part then return {} end
+  if not last_part then return {}, 0 end
 
   local parts, search_index = vim._expand_pat_get_parts(last_part)
 
@@ -568,11 +568,11 @@ function vim._expand_pat(pat, env)
   local final_env = env
   for _, part in ipairs(parts) do
     if type(final_env) ~= 'table' then
-      return {}
+      return {}, 0
     end
 
     -- Normally, we just have a string
-    --  Just attempt to get the string directly from the environment
+    -- Just attempt to get the string directly from the environment
     if type(part) == "string" then
       final_env = rawget(final_env, part)
     else
@@ -584,32 +584,32 @@ function vim._expand_pat(pat, env)
       -- -> _G[MY_VAR] -> "api"
       local result_key = part[1]
       if not result_key then
-        return {}
+        return {}, 0
       end
 
       local result = rawget(env, result_key)
 
       if result == nil then
-        return {}
+        return {}, 0
       end
 
       final_env = rawget(final_env, result)
     end
 
     if not final_env then
-      return {}
+      return {}, 0
     end
   end
 
   local result = vim.tbl_map(function(v)
-    return prefix_match_pat .. v
+    return v
   end, vim.tbl_filter(function(name)
     return string.find(name, match_pat) ~= nil
   end, vim.tbl_keys(final_env)))
 
   table.sort(result)
 
-  return result
+  return result, #prefix_match_pat
 end
 
 vim._expand_pat_get_parts = function(lua_string)