tightened rules for specifying modifiers

* Instead of separate stand-alone commands, they are now allowed only immediately
  in front of the commands that accept them.
* The order is still insignificant if both `@` and `:` are accepted.
* The number of colon modifiers is now also checked.
  We basically get this for free.
* `@` has syntactic significance, so it could not be set conditionally anyway.
  Still, it was possible to provoke bugs were `@` was interpreted conditionally
  as in `@ 2<I/foo/$>`.
* Even when not causing bugs, a mistyped `@` would often influence the
  __next__ command, causing unexpected behavior, for instance when
  typing `@(233C)W`.
* While it was theoretically possible to set `:` conditionally, it could also
  be "passed through" accidentally to some command where it wasn't expected as in
  `:Ifoo$ C`.
  I do not know of any real useful application or idiom of a conditionally set `:`.
  If there would happen to be some kind of useful application, `:'` and `:|` could
  be re-allowed easily, though.
* I was condidering introducing a common parser state for modified commands,
  but that would have been tricky and introduce a lot of redundant command lists.
  So instead, we now simply everywhere check for excess modifiers.
  To simplify this task, teco_machine_main_transition_t now contains flags
  signaling whether the transition is allowed with `@` or `:` modifiers set.
  It currently only has to be checked in the start state, after `E` and `F`.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/parser.c b/src/parser.c
index f4f7595..044a741 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -355,6 +355,13 @@ teco_machine_main_transition_input(teco_machine_main_t *ctx,
 		return NULL;
 	}
 
+	if ((ctx->modifier_at && !transitions[chr].modifier_at) ||
+	    (ctx->mode == TECO_MODE_NORMAL &&
+	     ctx->modifier_colon > transitions[chr].modifier_colon)) {
+		teco_error_modifier_set(error, chr);
+		return NULL;
+	}
+
 	if (ctx->mode == TECO_MODE_NORMAL && transitions[chr].transition_cb) {
 		/*
 		 * NOTE: We could also just let transition_cb return a boolean...