Allow backticks in variables defined through pattern matching

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scala> trait HasType{ var `type`: String }
defined trait HasType

Would be nice if that compiled:

scala> new HasType{ var Some(`type`) = Some("foo") }
<console>:10: error: stable identifier required, but $anon.this.`type` found.
              new HasType{ var Some(`type`) = Some("foo") }
                                    ^

Workaround:

scala> new HasType{ var Some(t) = Some("foo"); var `type`= t }
res7: HasType{def t: String; def t_=(x$1: String): Unit} = $anon$1@38c60a18

I am programmatically generating Scala code, so the workaround means a corner case in the code generator.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-8044?orig=1
Reporter: @cvogt

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@cvogt said:
Already has different semantics. Change wouldn't make sense.

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@retronym said:
It might be possible to extend the grammar to allow this in pattern binders:

I think we could change:

Pattern2 ::= varid ‘@’ Pattern3

to:

Pattern2 ::= id ‘@’ Pattern3

Which would admit both of:

scala> val Some(Tpe @ _) = Some(1)
<console>:1: error: ')' expected but '@' found.
       val Some(Tpe @ _) = Some(1)
                    ^

scala> val Some(`type` @ _) = Some(1)
<console>:1: error: ')' expected but '@' found.
       val Some(`type` @ _) = Some(1)
                       ^

Perhaps you can think over this proposal critically. If you can make a case that it doesn't introduce ambiguity, lets discuss at the Scala meeting.

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@cvogt said:
Nice idea! In my case, I worked around it using positional access on tuples for now, getting away without special casing. I re-open the ticket as Improvement/Trivial, so somebody else can pick up the topic if interested.

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@som-snytt said:
This is the narrower change of allowing backquoted idents that still look like varids.

scala/scala#4935