Grammar – Consistency & Cleanup

[Nigel-Ecma]

Up to Standard v5 the C# grammar was defined using a custom BNF-like grammar which supported optional and recursion, starting with Standard v6 the ANTLR grammar notation was adopted which added support for repetition. As of now the C# grammar has well almost 70 rules using repetition which has replaced unnecessary recursion.

In general language constructs which are left-associative are often described using left-recursive grammar rules which visualised as trees produce left-deep structures – e.g. this is the case for many arithmetic operators. Similarly right-associative constructs may be described by right-recursive rules which visualised produce right-deep structures. Finally list-like constructs are often described using repetition and visualised produced wide-flater trees – e.g. think argument lists, type parameter lists etc.

In v5 the list-like constructs where often represented by left-recursion as there was no repetition, from v6 such rules have been replaced by those using repetition.

This PR is the first of a number to pickup the stragglers, v5-era list-like structures described using left-recursion. Further a number of these rules have similar “cousins” within the grammar which have long made since made the transition and the dissimilarity in approach due to these straggles make the grammar as a whole less consistent.

As of today there are just 7 stragglers and 1 semi-straggler (it seems to have started transition and faltered).

This first PR handles: expression_list, query_body_clauses, type_parameters, and variant_type_parameters

Review Notes:

You only need to consider the changes to the *.md files in standard; the other files are machine-generated updates to parsing test samples describing the new expected parse for some samples. If you wish to see visualisations of the changes you may download the changed *.svg files in the PR and the current versions of them in draft-v8 and view them side-by-side (multiple monitors helps!)

[jskeet]

I hadn't expected to understand this PR, but I think I actually do. Shocker! (That doesn't mean it shouldn't be carefully reviewed by others, mind you.)

[BillWagner]

I reviewed the grammar changes closely, but didn't look much at the changes in the testing files.

I like the grammar updates. Those look great.

I'll approve as well.

@jskeet Can we merge this at tomorrow's meeting?

[jskeet]

@BillWagner

@jskeet Can we merge this at tomorrow's meeting?

That's my hope, yes :)