[RFC FS-1114] Make long-established deprecation warning messages into errors

[dsyme]

Implements https://github.com/fsharp/fslang-design/blob/main/RFCs/FS-1114-ml-compat-revisions.md

• get it green

[dsyme]

@KevinRansom This is now ready (though I know you're prioritizing the F# 6.0 labelling, that comes first).

The revisions go into preview with this PR. These don't have to be part of F# 6.0, happy for you to decide when to integrate

The PR also adds LangVersion to LexBuffer and this simplifies the many places we pass functions through. FCS now respects the language version for ParseFile operations, e.g. if one comes in explicitly via the ParsingOptions (which will stem from project options). This is correct API behaviour and the tests have been adjusted for it, though it won't change any actual IDE behaviour since no IDEs just parse files, they always ParseAndCheck files.

[auduchinok]

though it won't change any actual IDE behaviour since no IDEs just parse files, they always ParseAndCheck files

Just for the record, we use ParseFile a lot in Rider.

[dsyme]

Just for the record, we use ParseFile a lot in Rider.

Right, I'm assuming you still collect diagnostics from CheckFile (of course).

Anyway either way it's still right that ParseFile respect language version.

[auduchinok]

Right, I'm assuming you still collect diagnostics from CheckFile (of course).

We currently report parse and type check errors separately, and the parse ones come from ParseFile. It was implemented this way before the LangVersion was introduced, and I didn't know ParseFile worked differently these days.

It seems we have to either use ParseAndCheck for parse errors too, or to just wait until this PR is merged. Given we have some time before the next release, I'll probably just wait for this PR to land.

[dsyme]

We currently report parse and type check errors separately, and the parse ones come from ParseFile. It was implemented this way before the LangVersion was introduced, and I didn't know ParseFile worked differently these days.

Today, ParseFile effectively uses preview language version

• FSharpParsingOptions doesn't have any langversion info.

• When parsing "lexbuf.SupportsFeature" is implemented as a lambda returning true, meaning all features are considered supported

In practice I don't think there's a case where this matters today. However with this PR we start to emit errors for the long-deprecated features, but that depends on langversion, so it's important to pass the right langversion through.

[KevinRansom]

Thanks for this