feat(autocmds): retrieve lua callback (#18642)

add a new `callback` field to `nvim_get_autocmds`

5 files changed, 112 insertions, 38 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 2c75acbe1f..e47c5cbd6f 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -3610,7 +3610,11 @@ nvim_get_autocmds({*opts})                               *nvim_get_autocmds()*
                     • group_name (string): the autocommand group name.
                     • desc (string): the autocommand description.
                     • event (string): the autocommand event.
-                    • command (string): the autocommand command.
+                    • command (string): the autocommand command. Note: this
+                      will be empty if a callback is set.
+                    • callback (function|string|nil): Lua function or name of
+                      a Vim script function which is executed when this
+                      autocommand is triggered.
                     • once (boolean): whether the autocommand is only run
                       once.
                     • pattern (string): the autocommand pattern. If the
diff --git a/src/nvim/api/autocmd.c b/src/nvim/api/autocmd.c
index 19b4119344..3a35e49dc8 100644
--- a/src/nvim/api/autocmd.c
+++ b/src/nvim/api/autocmd.c
@@ -66,7 +66,9 @@ static int64_t next_autocmd_id = 1;
 ///             - group_name (string): the autocommand group name.
 ///             - desc (string): the autocommand description.
 ///             - event (string): the autocommand event.
-///             - command (string): the autocommand command.
+///             - command (string): the autocommand command. Note: this will be empty if a callback is set.
+///             - callback (function|string|nil): Lua function or name of a Vim script function
+///             which is executed when this autocommand is triggered.
 ///             - once (boolean): whether the autocommand is only run once.
 ///             - pattern (string): the autocommand pattern.
 ///             If the autocommand is buffer local |autocmd-buffer-local|:
@@ -280,9 +282,28 @@ Array nvim_get_autocmds(Dict(get_autocmds) *opts, Error *err)
           PUT(autocmd_info, "desc", CSTR_TO_OBJ(ac->desc));
         }
 
-        PUT(autocmd_info,
-            "command",
-            STRING_OBJ(cstr_as_string(aucmd_exec_to_string(ac, ac->exec))));
+        if (ac->exec.type == CALLABLE_CB) {
+          PUT(autocmd_info, "command", STRING_OBJ(STRING_INIT));
+
+          Callback *cb = &ac->exec.callable.cb;
+          switch (cb->type) {
+          case kCallbackLua:
+            if (nlua_ref_is_function(cb->data.luaref)) {
+              PUT(autocmd_info, "callback", LUAREF_OBJ(api_new_luaref(cb->data.luaref)));
+            }
+            break;
+          case kCallbackFuncref:
+          case kCallbackPartial:
+            PUT(autocmd_info, "callback", STRING_OBJ(cstr_as_string(callback_to_string(cb))));
+            break;
+          default:
+            abort();
+          }
+        } else {
+          PUT(autocmd_info,
+              "command",
+              STRING_OBJ(cstr_as_string(xstrdup(ac->exec.callable.cmd))));
+        }
 
         PUT(autocmd_info,
             "pattern",
@@ -442,7 +463,8 @@ Integer nvim_create_autocmd(uint64_t channel_id, Object event, Dict(create_autoc
     // not do that.
 
     Object *callback = &opts->callback;
-    if (callback->type == kObjectTypeLuaRef) {
+    switch (callback->type) {
+    case kObjectTypeLuaRef:
       if (callback->data.luaref == LUA_NOREF) {
         api_set_error(err,
                       kErrorTypeValidation,
@@ -459,10 +481,12 @@ Integer nvim_create_autocmd(uint64_t channel_id, Object event, Dict(create_autoc
 
       cb.type = kCallbackLua;
       cb.data.luaref = api_new_luaref(callback->data.luaref);
-    } else if (callback->type == kObjectTypeString) {
+      break;
+    case kObjectTypeString:
       cb.type = kCallbackFuncref;
       cb.data.funcref = string_to_cstr(callback->data.string);
-    } else {
+      break;
+    default:
       api_set_error(err,
                     kErrorTypeException,
                     "'callback' must be a lua function or name of vim function");
diff --git a/src/nvim/autocmd.c b/src/nvim/autocmd.c
index 31efce13f6..69f01afcb6 100644
--- a/src/nvim/autocmd.c
+++ b/src/nvim/autocmd.c
@@ -2477,32 +2477,6 @@ bool autocmd_delete_id(int64_t id)
 //  AucmdExecutable Functions
 // ===========================================================================
 
-/// Generate a string description of a callback
-static char *aucmd_callback_to_string(Callback cb)
-{
-  // NOTE: this function probably belongs in a helper
-
-  size_t msglen = 100;
-  char *msg = (char *)xmallocz(msglen);
-
-  switch (cb.type) {
-  case kCallbackLua:
-    snprintf(msg, msglen, "<lua: %d>", cb.data.luaref);
-    break;
-  case kCallbackFuncref:
-    // TODO(tjdevries): Is this enough space for this?
-    snprintf(msg, msglen, "<vim function: %s>", cb.data.funcref);
-    break;
-  case kCallbackPartial:
-    snprintf(msg, msglen, "<vim partial: %s>", cb.data.partial->pt_name);
-    break;
-  default:
-    snprintf(msg, msglen, "%s", "");
-    break;
-  }
-  return msg;
-}
-
 /// Generate a string description for the command/callback of an autocmd
 char *aucmd_exec_to_string(AutoCmd *ac, AucmdExecutable acc)
   FUNC_ATTR_PURE
@@ -2511,7 +2485,7 @@ char *aucmd_exec_to_string(AutoCmd *ac, AucmdExecutable acc)
   case CALLABLE_EX:
     return xstrdup(acc.callable.cmd);
   case CALLABLE_CB:
-    return aucmd_callback_to_string(acc.callable.cb);
+    return callback_to_string(&acc.callable.cb);
   case CALLABLE_NONE:
     return "This is not possible";
   }
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index 2c76741891..97726da5f4 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -1205,6 +1205,30 @@ void callback_copy(Callback *dest, Callback *src)
   }
 }
 
+/// Generate a string description of a callback
+char *callback_to_string(Callback *cb)
+{
+  size_t msglen = 100;
+  char *msg = (char *)xmallocz(msglen);
+
+  switch (cb->type) {
+  case kCallbackLua:
+    snprintf(msg, msglen, "<lua: %d>", cb->data.luaref);
+    break;
+  case kCallbackFuncref:
+    // TODO(tjdevries): Is this enough space for this?
+    snprintf(msg, msglen, "<vim function: %s>", cb->data.funcref);
+    break;
+  case kCallbackPartial:
+    snprintf(msg, msglen, "<vim partial: %s>", cb->data.partial->pt_name);
+    break;
+  default:
+    snprintf(msg, msglen, "%s", "");
+    break;
+  }
+  return msg;
+}
+
 /// Remove watcher from a dictionary
 ///
 /// @param  dict  Dictionary to remove watcher from.
diff --git a/test/functional/api/autocmd_spec.lua b/test/functional/api/autocmd_spec.lua
index 491dac9f35..5dfcd09438 100644
--- a/test/functional/api/autocmd_spec.lua
+++ b/test/functional/api/autocmd_spec.lua
@@ -135,17 +135,22 @@ describe('autocmd api', function()
         local desc = 'Can show description'
         meths.set_var('desc', desc)
 
-        exec_lua([[
+        local result = exec_lua([[
           local callback = function() print 'Should Not Have Errored' end
           vim.api.nvim_create_autocmd("BufReadPost", {
             pattern = "*.py",
             callback = callback,
             desc = vim.g.desc,
           })
+          local aus = vim.api.nvim_get_autocmds({ event = 'BufReadPost' })
+          local first = aus[1]
+          return {
+            desc = first.desc,
+            cbtype = type(first.callback)
+          }
         ]])
 
-        eq(desc, meths.get_autocmds({ event = 'BufReadPost' })[1].desc)
-        matches('<lua: %d+>', meths.get_autocmds({ event = 'BufReadPost' })[1].command)
+        eq({ desc = desc, cbtype = 'function' }, result)
       end)
 
       it('will not add a description unless it was provided', function()
@@ -465,6 +470,49 @@ describe('autocmd api', function()
         -- 3-7 for the 5 we make in the autocmd
         eq({1, 2, 3, 4, 5, 6, 7}, bufs)
       end)
+
+      it('can retrieve a callback from an autocmd', function()
+        local content = 'I Am A Callback'
+        meths.set_var('content', content)
+
+        local result = exec_lua([[
+          local cb = function() return vim.g.content end
+          vim.api.nvim_create_autocmd("User", {
+            pattern = "TestTrigger",
+            desc = "A test autocommand with a callback",
+            callback = cb,
+          })
+          local aus = vim.api.nvim_get_autocmds({ event = 'User', pattern = 'TestTrigger'})
+          local first = aus[1]
+          return {
+            cb = {
+              type = type(first.callback),
+              can_retrieve = first.callback() == vim.g.content
+            }
+          }
+        ]])
+
+        eq("function", result.cb.type)
+        eq(true, result.cb.can_retrieve)
+      end)
+
+      it('will return an empty string as the command for an autocmd that uses a callback', function()
+        local result = exec_lua([[
+          local callback = function() print 'I Am A Callback' end
+          vim.api.nvim_create_autocmd("BufWritePost", {
+            pattern = "*.py",
+            callback = callback,
+          })
+          local aus = vim.api.nvim_get_autocmds({ event = 'BufWritePost' })
+          local first = aus[1]
+          return {
+            command = first.command,
+            cbtype = type(first.callback)
+          }
+        ]])
+
+        eq({ command = "", cbtype = 'function' }, result)
+      end)
     end)
 
     describe('groups', function()