Improve Expr.toString and Type.toString

[nicolasstucki]

With this change, the toString can return the same as the show method.

We now capture the context in each Expr and Type instead of the Scope. This context can be used to compute the Scope.

Note that the context that is captured is the same one that is captured by the Quotes instance. As the expressions created with this Quotes should not escape the splice the created that Quotes, the Expr should not outlive the instance of Quotes. Therefore the captured context should not leak out of the macro expansion (or nested splice).

Behavior

• This changes the default string representation of quoted expressions

def printExpr(e: Expr[T])(using Quotes) =
  println(e)
printExpr('{ f(x) })

// previous behavior
'{ ... }

// new behavior
'{ f(x) }

• This also work well with pattern matching

'{ f(x) } match
  case '{ f(1) } => ...
  case '{ f(2) } => ...

// previous behavior
scala.MatchError: '{ ... }  (of class scala.quoted.Expr)
  at Foo.test(Foo$3:4)
  ...

// new behavior
MatchError: '{ f(x) } (of class scala.quoted.Expr)
  at Foo.test(Foo$3:4)
  ...

• This would also simplify debuggers as they could directly show the string

[nicolasstucki]

test performance with #quotes please: 779a382

[dottybot]

performance test scheduled for 779a382: 1 job(s) in queue, 0 running.

[nicolasstucki]

test performance with #quotes please

[dottybot]

performance test scheduled: 1 job(s) in queue, 1 running.

[dottybot]

performance test scheduled: 1 job(s) in queue, 1 running.

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/16556/ to see the changes.

Benchmarks is based on merging with main (779a382)

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/16556/ to see the changes.

Benchmarks is based on merging with main (779a382)

[odersky]

What data is stored in a Context? In principle it looks cleaner to me to separate data types
like Expr and Type from the Context that prints them.

I am not seeing the motivation for the change. Can you describe what was the toString behavior before? And what is it now?

[odersky]

I am still not sure this is the right way to do it. Normally, it's best to leave toString as the low-level debug info that simple shows the tree as is. I.e. not {...} but a case class term instead. And then there is a high-level show method that takes
a context and prints the tree in a high-level syntax. Why is that approach not applicable here?

[nicolasstucki]

Replaced with #16663