Move actiont checking from codegen to ast validation.

[ratmice]

Here is an attempt to validate actiont earlier,
adding it to YaccGrammarError.

I'm uncertain it's possible to trigger for YaccKind::Grmtools I would imagine you'd get a syntax error before it could complete_and_validate. So I checked that with a manually constructed AST.

[ratmice]

There is a similar error here that should probably also be moved in this patch

[ratmice]

Should be fixed in 9e956c2

[ratmice]

Ditto for this error.

[ratmice]

Should be fixed in 6313b96 and tested in ca3a9b1

And with that the diag variable becomes unused and can be removed from the last stages of codegen.

[ratmice]

Would UnrecognizedActionVariable be better?

[ratmice]

I renamed it in c2d027c

[ratmice]

We could consider making this boolean check a method on YaccKind?
With a different name like YaccKind::requires_actions?

I think it might also simplify a similar check in CTParserBulder.

[ratmice]

This else is probably a bit wonky, but it doesn't seem totally wrong in that we know each match is going to be at least 2?

There is one corner case here though where we get a weird span.
If we slightly modify the test I added:

(Modified test)

            r#"
%token a
%%
start -> () : "a" {$};
"#,
        );
        assert_eq!(
            ast_validity.errors(),
            vec![YaccGrammarError {
                kind: YaccGrammarErrorKind::UnrecognisedActionVariable,
                spans: vec![Span::new(33, 33)],
            }]
        );

We see that the cursor with the removed space before the $ points to a zero length span
beginning right after the $ at the very end of the action. I would probably expect a span of like (32, 33). Morning brain hasn't started working yet to figure out what's going on with this calculation.

        let ast_validity = ASTWithValidityInfo::new(
            YaccKind::Grmtools,
            r#"
%token a
%%
start -> () : "a" { $foo; };
"#,
        );
        assert_eq!(
            ast_validity.errors(),
            vec![YaccGrammarError {
                kind: YaccGrammarErrorKind::UnrecognisedActionVariable,
                spans: vec![Span::new(33, 37)],
            }]
        );