Attempt to subtract with overflow

[andrewbaxter]

Describe the bug
The code panics at

                    .split_off(self.res_stack.len() - 3usize)

from the generated code:

            ProdKind::InlineElStrong => {
                let mut i = self
                    .res_stack
                    .split_off(self.res_stack.len() - 3usize)
                    .into_iter();
                match (i.next().unwrap(), i.next().unwrap(), i.next().unwrap()) {
                    (
                        Symbol::NonTerminal(NonTerminal::StrongDelim(p0)),
                        Symbol::NonTerminal(NonTerminal::Inline(p1)),
                        Symbol::NonTerminal(NonTerminal::StrongDelimOpt(p2)),
                    ) => {
                        NonTerminal::InlineEl(
                            inline_actions::inline_el_strong(&*context, p0, p1, p2),
                        )
                    }
                    _ => panic!("Invalid symbol parse stack data."),
                }
            }

It's possible that this is a grammar issue, but it's not clear what happened from info in the panic itself.

Here's the grammar:

Inline: InlineEl*;
InlineEl: prefix=StrongDelim children=Inline suffix=StrongDelim? {Strong, 11, left}
        | prefix=EmphasisDelim children=Inline suffix=EmphasisDelim? {Emphasis, 11, left} 
        | title_prefix=LinkTitlePrefix title=Inline continuation=Link1? {Link , 11, left}
        | prefix=CodeDelim text=CodeChar* suffix=CodeDelim? {Code, 11, left} 
        | text=TextChar+ {Text, 9, left};

StrongDelim: StrongT;

EmphasisDelim: EmphasisT;

LinkTitlePrefix: LinkTitlePrefixT;
LinkTitleSuffix: LinkTitleSuffixT;
LinkAddressPrefix: LinkAddressPrefixT;
LinkAddressSuffix: LinkAddressSuffixT;
Link1: title_suffix=LinkTitleSuffix address=LinkAddress?;
LinkAddress: prefix=LinkAddressPrefix address=LinkAddressChar* suffix=LinkAddressSuffix?;
LinkAddressChar: LinkAddressCharT | EscapedChar;

CodeDelim: CodeDelimT;
CodeChar: CodeCharT | EscapedChar;

TextChar: TextCharT | EscapedChar;

EscapeChar: EscapeT;
EscapedChar: prefix=EscapeChar text=AnyCharT;

Layout: Empty;

terminals
Empty: "";
EscapeT: "\\";
AnyCharT: /./;
TextCharT: /[^*_`\\]/;
CodeDelimT: "`";
CodeCharT: /[^`\\]/;
LinkTitlePrefixT: "[";
LinkTitleSuffixT: "](";
LinkAddressPrefixT: "(";
LinkAddressSuffixT: ")";
LinkAddressCharT: /[^)\\]/;
StrongT: "*";
EmphasisT: "_";

So foremost this is a bug about error messages.

[igordejanovic]

Thanks for the report. I don't think it could be a grammar issue. It smells to me like a bug in code gen. Could you make a PR with a failing regression test? Probably the best place to put it is in the tests crate. Something like src/regressions/issue_16_subtract_overflow_panic.

[andrewbaxter]

Oh sure! Sorry, it may take me a couple days. Thanks for the pointers for making the test.

Although TBH I'm not confident I have the exact text that caused the issue on hand... I'll see if I can reproduce it. I should have included the text too.

[igordejanovic]

Thanks much for the PR! No problem at all for the delays. I'm also sometimes very slow in responses depending on other tasks I have so no worries.

[igordejanovic]

I figured out what the problem is but it requires a bit of work. Only default builder for GLR is affected. Thus, the workaround until I fix the issue is to either use generic builder or LR parsing.

[igordejanovic]

@andrewbaxter I've finished rework of the generator. This issue is resolved. Thanks again for the regression test. I'll make a bugfix release in the following days.

[andrewbaxter]

Awesome, thanks! 🙇