vim-patch:8.1.1113: making an autocommand trigger once is not so easy

Problem:    Making an autocommand trigger once is not so easy.
Solution:   Add the ++once argument.  Also add ++nested as an alias for
            "nested". (Justin M. Keyes, closes vim/vim#4100)
eb93f3f0e2

src/nvim/fileio.c

@@ -6061,17 +6061,30 @@ void do_autocmd(char_u *arg_in, int forceit)
     for (size_t i = 0; i < 2; i++) {
       if (*cmd != NUL) {
         // Check for "++once" flag.
-        if (!once && STRNCMP(cmd, "++once", 6) == 0 && ascii_iswhite(cmd[6])) {
+        if (STRNCMP(cmd, "++once", 6) == 0 && ascii_iswhite(cmd[6])) {
+          if (once) {
+            EMSG2(_(e_duparg2), "++once");
+          }
           once = true;
           cmd = skipwhite(cmd + 6);
         }
+
         // Check for "++nested" flag.
-        if (!nested
-            && ((STRNCMP(cmd, "++nested", 8) == 0 && ascii_iswhite(cmd[8]))
-                // Deprecated form (without "++").
-                || (STRNCMP(cmd, "nested", 6) == 0 && ascii_iswhite(cmd[6])))) {
+        if ((STRNCMP(cmd, "++nested", 8) == 0 && ascii_iswhite(cmd[8]))) {
+          if (nested) {
+            EMSG2(_(e_duparg2), "++nested");
+          }
           nested = true;
-          cmd = skipwhite(cmd + ('+' == cmd[0] ? 8 : 6));
+          cmd = skipwhite(cmd + 8);
+        }
+
+        // Check for the old (deprecated) "nested" flag.
+        if (STRNCMP(cmd, "nested", 6) == 0 && ascii_iswhite(cmd[6])) {
+          if (nested) {
+            EMSG2(_(e_duparg2), "nested");
+          }
+          nested = true;
+          cmd = skipwhite(cmd + 6);
         }
       }
     }

src/nvim/globals.h

@@ -931,6 +931,7 @@ EXTERN char_u e_interr[] INIT(= N_("Interrupted"));
 EXTERN char_u e_invaddr[] INIT(= N_("E14: Invalid address"));
 EXTERN char_u e_invarg[] INIT(= N_("E474: Invalid argument"));
 EXTERN char_u e_invarg2[] INIT(= N_("E475: Invalid argument: %s"));
+EXTERN char_u e_duparg2[] INIT(= N_("E983: Duplicate argument: %s"));
 EXTERN char_u e_invexpr2[] INIT(= N_("E15: Invalid expression: %s"));
 EXTERN char_u e_invrange[] INIT(= N_("E16: Invalid range"));
 EXTERN char_u e_invcmd[] INIT(= N_("E476: Invalid command"));

src/nvim/testdir/test_autocmd.vim

@@ -1308,3 +1308,73 @@ func Test_Changed_FirstTime()
   call delete('Xchanged.txt')
   bwipe!
 endfunc
+
+func Test_autocmd_nested()
+  let g:did_nested = 0
+  augroup Testing
+    au WinNew * edit somefile
+    au BufNew * let g:did_nested = 1
+  augroup END
+  split
+  call assert_equal(0, g:did_nested)
+  close
+  bwipe! somefile
+
+  " old nested argument still works
+  augroup Testing
+    au!
+    au WinNew * nested edit somefile
+    au BufNew * let g:did_nested = 1
+  augroup END
+  split
+  call assert_equal(1, g:did_nested)
+  close
+  bwipe! somefile
+
+  " New ++nested argument works
+  augroup Testing
+    au!
+    au WinNew * ++nested edit somefile
+    au BufNew * let g:did_nested = 1
+  augroup END
+  split
+  call assert_equal(1, g:did_nested)
+  close
+  bwipe! somefile
+
+  augroup Testing
+    au!
+  augroup END
+
+  call assert_fails('au WinNew * ++nested ++nested echo bad', 'E983:')
+  call assert_fails('au WinNew * nested nested echo bad', 'E983:')
+endfunc
+
+func Test_autocmd_once()
+  " Without ++once WinNew triggers twice
+  let g:did_split = 0
+  augroup Testing
+    au WinNew * let g:did_split += 1
+  augroup END
+  split
+  split
+  call assert_equal(2, g:did_split)
+  call assert_true(exists('#WinNew'))
+  close
+  close
+
+  " With ++once WinNew triggers once
+  let g:did_split = 0
+  augroup Testing
+    au!
+    au WinNew * ++once let g:did_split += 1
+  augroup END
+  split
+  split
+  call assert_equal(1, g:did_split)
+  call assert_false(exists('#WinNew'))
+  close
+  close
+
+  call assert_fails('au WinNew * ++once ++once echo bad', 'E983:')
+endfunc