Fix a bug with named NEVER_MATCH expressions #454
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Unfortunately, the new error also not so good, because it is misleading. The grammar
start 'start' = []cannot have any expectations because it just cannot match any input. Probably, it would be better to emit compiler error here instead. This grammar does not expect "start" rule at this position, it expect literally nothing. Even EOF is not expected there.
| @@ -618,7 +618,7 @@ function generateBytecode(ast, options) { | |||
| [op.SILENT_FAILS_ON], | |||
| generate(node.expression, context), | |||
| [op.SILENT_FAILS_OFF], | |||
| buildCondition(match, [op.IF_ERROR], [op.FAIL, nameIndex], []) | |||
| buildCondition(-match, [op.IF_ERROR], [op.FAIL, nameIndex], []) | |||
| ); | |||
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Good catch! The bug probably was introduced during rebase while adapt initial PR to the new code after another merged PR.
Actually, the whole buildSequence could be replaced by [op.FAIL, nameIndex] if node always fail and there are no actions or semantic predicates (because they can have side effects), but anyway, it is better to do in a separate pass.
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if node always fail and there are no actions or semantic predicates (because they can have side effects)
There are already comments about adding side-effect analysis so we can do that kind of thing...
But that was true whether or not it's a
I guess thats ok if it's a start rule that always fails - but my examples only used start rules to exemplify the problem. You could use it as a catch all where a promising start goes off the rails: Ok, its still not a great example, but it could be useful to have a |
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@Mingun did you end up being happy with where this patch is at the moment? |
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Yes, please merge. |
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I've got a clean rebase on top of main as it sits at the moment. I'm going to try pushing it to @markw65 's branch, which is likely going to fail. If so, I guess I'll start a new PR with my copy of the branch, and try to ensure the authorship is kept intact as much as possible. |
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OK, that looks like it worked. Merging. |
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Sorry, I've been occupied elsewhere, but thanks for merging. |
Found while working on #452.
The condition was backwards, so the error got misreported:
Before the fix:
After the fix:
There was already a test, but it was testing for the incorrect result...