No line numbers for errors discovered in lrpar/ctbuilder.rs

[ltratt]

The error messages we get from yacc/parser.rs are really helpful, but if the text gets through to ctbuilder.rs the errors are less helpful. Consider:

FuncAttrs -> Result<Vec<AstFuncAttr>, Box<dyn Error>>:
    FuncAttrs FuncAttr { flattenr($1, $) }

The error one gets is:

Unknown text following '$' operator: $)

without a line number (and also repeating the $ character; I think the relevant code &pre_action[last + off..] is missing a +1). That can make tracking the problem down a little frustrating. Given we have token_span in YaccGrammar can we also record and pass through the span of action text? Then ctbuilder.rs could give line/column warnings for such errors.

[ratmice]

I believe we should be able to add a function like action_span() perhaps, but I'll have to look into it!

[ltratt]

Thanks!

[ratmice]

I think the biggest difficulty here is SemVer compatibility, it looks like both
GrammarAST::add_prod and struct Production need changes.

I think the right thing to do is pub action: Option<String>, into pub action: Option<(String, Span)>,

I think if we tried to separate them into distinct fields, such as adding pub action_span: Option<Span> to Production we end up with cases like Some(span) but no action: None.

I don't think YaccGrammar requires any incompatible changes though, there we can just add a new fn action_span. But unfortunately (as per the above) it doesn't look like we currently store that span in the AST anywhere.

I'll probably look at getting some simpler changes before attempting this one.

[ltratt]

I think the biggest difficulty here is SemVer compatibility, it looks like both
GrammarAST::add_prod and struct Production need changes.

I think that's a bullet worth biting. Maybe we can find the other bits where we give errors without line numbers and do all of them in one go?