fix(api): generic error messages, not using TRY_WRAP #31596

Problem:
- API functions using `try_start` directly, do not surface the
  underlying error message, and instead show generic messages.
- Error-handling code is duplicated in the API impl.
- Failure modes are not tested.

Solution:
- Use `TRY_WRAP`.
- Add tests.

src/nvim/api/vim.c

@@ -669,16 +669,9 @@ void nvim_set_current_dir(String dir, Error *err)
   memcpy(string, dir.data, dir.size);
   string[dir.size] = NUL;
 
-  try_start();
-
-  if (!changedir_func(string, kCdScopeGlobal)) {
-    if (!try_end(err)) {
-      api_set_error(err, kErrorTypeException, "Failed to change directory");
-    }
-    return;
-  }
-
-  try_end(err);
+  TRY_WRAP(err, {
+    changedir_func(string, kCdScopeGlobal);
+  });
 }
 
 /// Gets the current line.
@@ -942,14 +935,9 @@ void nvim_set_current_win(Window window, Error *err)
     return;
   }
 
-  try_start();
-  goto_tabpage_win(win_find_tabpage(win), win);
-  if (!try_end(err) && win != curwin) {
-    api_set_error(err,
-                  kErrorTypeException,
-                  "Failed to switch to window %d",
-                  window);
-  }
+  TRY_WRAP(err, {
+    goto_tabpage_win(win_find_tabpage(win), win);
+  });
 }
 
 /// Creates a new, empty, unnamed buffer.
@@ -1208,14 +1196,9 @@ void nvim_set_current_tabpage(Tabpage tabpage, Error *err)
     return;
   }
 
-  try_start();
-  goto_tabpage_tp(tp, true, true);
-  if (!try_end(err) && tp != curtab) {
-    api_set_error(err,
-                  kErrorTypeException,
-                  "Failed to switch to tabpage %d",
-                  tabpage);
-  }
+  TRY_WRAP(err, {
+    goto_tabpage_tp(tp, true, true);
+  });
 }
 
 /// Pastes at cursor (in any mode), and sets "redo" so dot (|.|) will repeat the input. UIs call

src/nvim/api/vimscript.c

@@ -125,19 +125,17 @@ theend:
 ///
 /// On execution error: fails with Vimscript error, updates v:errmsg.
 ///
-/// Prefer using |nvim_cmd()| or |nvim_exec2()| over this. To evaluate multiple lines of Vim script
-/// or an Ex command directly, use |nvim_exec2()|. To construct an Ex command using a structured
-/// format and then execute it, use |nvim_cmd()|. To modify an Ex command before evaluating it, use
-/// |nvim_parse_cmd()| in conjunction with |nvim_cmd()|.
+/// Prefer |nvim_cmd()| or |nvim_exec2()| instead. To modify an Ex command in a structured way
+/// before executing it, modify the result of |nvim_parse_cmd()| then pass it to |nvim_cmd()|.
 ///
 /// @param command  Ex command string
 /// @param[out] err Error details (Vim error), if any
 void nvim_command(String command, Error *err)
   FUNC_API_SINCE(1)
 {
-  try_start();
-  do_cmdline_cmd(command.data);
-  try_end(err);
+  TRY_WRAP(err, {
+    do_cmdline_cmd(command.data);
+  });
 }
 
 /// Evaluates a Vimscript |expression|. Dicts and Lists are recursively expanded.
@@ -283,13 +281,11 @@ Object nvim_call_dict_function(Object dict, String fn, Array args, Arena *arena,
   bool mustfree = false;
   switch (dict.type) {
   case kObjectTypeString:
-    try_start();
-    if (eval0(dict.data.string.data, &rettv, NULL, &EVALARG_EVALUATE) == FAIL) {
-      api_set_error(err, kErrorTypeException,
-                    "Failed to evaluate dict expression");
-    }
-    clear_evalarg(&EVALARG_EVALUATE, NULL);
-    if (try_end(err)) {
+    TRY_WRAP(err, {
+      eval0(dict.data.string.data, &rettv, NULL, &EVALARG_EVALUATE);
+      clear_evalarg(&EVALARG_EVALUATE, NULL);
+    });
+    if (ERROR_SET(err)) {
       return rv;
     }
     // Evaluation of the string arg created a new dict or increased the

src/nvim/api/window.c

@@ -182,14 +182,9 @@ void nvim_win_set_height(Window window, Integer height, Error *err)
     return;
   }
 
-  if (height > INT_MAX || height < INT_MIN) {
-    api_set_error(err, kErrorTypeValidation, "Height value outside range");
-    return;
-  }
-
-  try_start();
-  win_setheight_win((int)height, win);
-  try_end(err);
+  TRY_WRAP(err, {
+    win_setheight_win((int)height, win);
+  });
 }
 
 /// Gets the window width
@@ -224,14 +219,9 @@ void nvim_win_set_width(Window window, Integer width, Error *err)
     return;
   }
 
-  if (width > INT_MAX || width < INT_MIN) {
-    api_set_error(err, kErrorTypeValidation, "Width value outside range");
-    return;
-  }
-
-  try_start();
-  win_setwidth_win((int)width, win);
-  try_end(err);
+  TRY_WRAP(err, {
+    win_setwidth_win((int)width, win);
+  });
 }
 
 /// Gets a window-scoped (w:) variable
@@ -436,15 +426,15 @@ Object nvim_win_call(Window window, LuaRef fun, Error *err)
   }
   tabpage_T *tabpage = win_find_tabpage(win);
 
-  try_start();
   Object res = OBJECT_INIT;
-  win_execute_T win_execute_args;
-  if (win_execute_before(&win_execute_args, win, tabpage)) {
-    Array args = ARRAY_DICT_INIT;
-    res = nlua_call_ref(fun, NULL, args, kRetLuaref, NULL, err);
-  }
-  win_execute_after(&win_execute_args);
-  try_end(err);
+  TRY_WRAP(err, {
+    win_execute_T win_execute_args;
+    if (win_execute_before(&win_execute_args, win, tabpage)) {
+      Array args = ARRAY_DICT_INIT;
+      res = nlua_call_ref(fun, NULL, args, kRetLuaref, NULL, err);
+    }
+    win_execute_after(&win_execute_args);
+  });
   return res;
 }