fix(api): do not pull a fast one for nvim_del_augroup_by_id

This is a bit more boilerplate because of painful impedance mismatch (is
augroup names the root source of truth? is ids the source of truth? who
knows? what does truth even mean?), but show an error reflecting what
the caller actually tried (they passed in an invalid id, not a null
string)

scripts/linterrcodes.lua

@@ -32,6 +32,7 @@ local dup_allowed = {
   E312 = 2,
   E317 = 4,
   E319 = 2,
+  E367 = 3,
   E423 = 3,
   E474 = 60,
   E475 = 6,

src/nvim/api/autocmd.c

@@ -663,8 +663,7 @@ void nvim_del_augroup_by_id(Integer id, Error *err)
   FUNC_API_SINCE(9)
 {
   TRY_WRAP(err, {
-    char *name = id == 0 ? NULL : augroup_name((int)id);
-    augroup_del(name, false);
+    augroup_del_by_id((int)id);
   });
 }
 
@@ -678,7 +677,7 @@ void nvim_del_augroup_by_name(String name, Error *err)
   FUNC_API_SINCE(9)
 {
   TRY_WRAP(err, {
-    augroup_del(name.data, false);
+    augroup_del(name.data, -1, false);
   });
 }
 

src/nvim/autocmd.c

@@ -421,6 +421,17 @@ int augroup_add(const char *name)
   return next_id;
 }
 
+void augroup_del_by_id(int id)
+{
+  char *name = id <= 0 ? NULL : augroup_name(id);
+  if (name == NULL) {
+    semsg(_("E367: No such group id: %d"), id);
+  } else {
+    // NB: this can still error, but the error might be "semantic" like "-- Deleted --"
+    augroup_del(name, id, false);
+  }
+}
+
 /// Delete the augroup that matches name.
 /// @param stupid_legacy_mode bool: This parameter determines whether to run the augroup
 ///     deletion in the same fashion as `:augroup! {name}` where if there are any remaining
@@ -432,11 +443,18 @@ int augroup_add(const char *name)
 ///     I did not consider this good behavior, so now when NOT in stupid_legacy_mode, we actually
 ///     delete these groups and their commands, like you would expect (and don't leave hanging
 ///     `--- DELETED ---` groups around)
-void augroup_del(char *name, bool stupid_legacy_mode)
+/// @param id_for_error  only to provide context for an error message:
+///                       if >= 0, we tried to look up the group by id
+///                       if < 0, only use `name` for error
+void augroup_del(char *name, int id_for_error, bool stupid_legacy_mode)
 {
   int group = augroup_find(name);
   if (group == AUGROUP_ERROR) {  // the group doesn't exist
-    semsg(_("E367: No such group: \"%s\""), name);
+    if (id_for_error > 0) {
+      semsg(_("E367: No such group id: %d \"%s\""), id_for_error, name);
+    } else {
+      semsg(_("E367: No such group: \"%s\""), name);
+    }
     return;
   } else if (group == current_augroup) {
     emsg(_("E936: Cannot delete the current group"));
@@ -548,7 +566,7 @@ void do_augroup(char *arg, bool del_group)
     if (*arg == NUL) {
       emsg(_(e_argreq));
     } else {
-      augroup_del(arg, true);
+      augroup_del(arg, -1, true);
     }
   } else if (STRICMP(arg, "end") == 0) {  // ":aug end": back to group 0
     current_augroup = AUGROUP_DEFAULT;

test/functional/api/autocmd_spec.lua

@@ -1671,13 +1671,13 @@ describe('autocmd api', function()
       eq('Vim:E367: No such group: "noexist"', pcall_err(api.nvim_del_augroup_by_name, 'noexist'))
 
       eq(false, exec_lua [[return pcall(vim.api.nvim_del_augroup_by_id, -12342)]])
-      eq('Vim:E367: No such group: "--Deleted--"', pcall_err(api.nvim_del_augroup_by_id, -12312))
+      eq('Vim:E367: No such group id: -12312', pcall_err(api.nvim_del_augroup_by_id, -12312))
 
       eq(false, exec_lua [[return pcall(vim.api.nvim_del_augroup_by_id, 0)]])
-      eq('Vim:E367: No such group: "[NULL]"', pcall_err(api.nvim_del_augroup_by_id, 0))
+      eq('Vim:E367: No such group id: 0', pcall_err(api.nvim_del_augroup_by_id, 0))
 
       eq(false, exec_lua [[return pcall(vim.api.nvim_del_augroup_by_id, 12342)]])
-      eq('Vim:E367: No such group: "[NULL]"', pcall_err(api.nvim_del_augroup_by_id, 12312))
+      eq('Vim:E367: No such group id: 12312', pcall_err(api.nvim_del_augroup_by_id, 12312))
     end)
 
     it('groups work with once', function()
@@ -1828,6 +1828,13 @@ describe('autocmd api', function()
       -- so now this works as expected
       eq(false, pcall(api.nvim_get_autocmds, { group = 'TEMP_ABCD' }))
       eq(0, #api.nvim_get_autocmds { event = 'BufReadPost' })
+
+      -- deleting an already deleted group gives NICE error message:
+      -- exact value of augroup_id here depends on defaults.lua and bullshit, splice it in!
+      eq(
+        'Vim:E367: No such group id: ' .. augroup_id .. ' "--Deleted--"',
+        pcall_err(api.nvim_del_augroup_by_id, augroup_id)
+      )
     end)
 
     it('api: should clear and not return any autocmds for delete groups by name', function()