Filter completions for record fields in patterns

[kerams]

Fixes#15889.

| { } and | { f = 1; g } do not recover gracefully and there is no match clause, let alone SynPat.Record. Didn't feel like fixing that here.

[vzarytovskii]

Nice

[auduchinok]

| { } and | { f = 1; g } do not recover gracefully and there is no match clause, let alone SynPat.Record. Didn't feel like fixing that here.

I can work on it if you want to wait a bit here or help me fix the code completion later.

[kerams]

I reckon that if you manage to return SynPat.Record ([], m) and SynPat.Record ([ oneField ], m)/SynPat.Record ([ oneField; SynPat.FromParseError (...) ], m) for the 2 clauses, completions will work nicely without any changes.

[psfinaki]

So this can be simplified after #15921?

[vzarytovskii]

Should auto-merge when comments are resolved.

[auduchinok]

@vzarytovskii If we decide to merge #15921 first, it would be better to double check that this PR doesn't need any updates.