Warn when named tuples resemble assignments

[mbovel]

This PR adds a warning for named tuples that look like assignment, such as (x = 1).

This is the first half to implement #21681. The second will be to add warnings for named arguments to infix method calls (as a separate PR?).

Started during the Spree of October 21st.

Closes #21770.

[som-snytt]

My quick test shows an unexpected error

Compilation failed for: tests/warn/infix-named-args.scala
-> following the diagnostics:
 at 5: None of the overloaded alternatives of method + in class Int with types
 (x: Double): Double
 (x: Float): Float
 (x: Long): Long
 (x: Int): Int
 (x: Char): Int
 (x: Short): Int
 (x: Byte): Int
 (x: String): String
match arguments ((x : Int))

for the test in

https://github.com/scala/scala3/pull/21565/files

[mbovel]

My quick test shows an unexpected error

def f = 42 + (x = 1)

-- [E134] Type Error: playground.scala:1:11 ------------------------------------
1 |def f = 42 + (x = 1)
  |        ^^^^
  |   None of the overloaded alternatives of method + in class Int with types
  |    (x: Double): Double
  |    (x: Float): Float
  |    (x: Long): Long
  |    (x: Int): Int
  |    (x: Char): Int
  |    (x: Short): Int
  |    (x: Byte): Int
  |    (x: String): String
  |   match arguments ((x : Int))

It is expected to have an error in this case, isn't it? I also get in on main.

We should add a warning to tell the user that (x = 1) is interpreted as a tuple in this case as suggested in #21681, but we haven't had the time to implement it yet.

[mbovel]

Also, we found that our naive use of ctx.scope.lookup it not complete enough. It seems it only looks in the current scope.

It doesn't work for example for:

object Test:
  var age: Int = 28
  (age = 29) // warn

@nicolasstucki suggests that we move our check to Typer and type the identifier there to resolve the symbol properly.

[mbovel]

@nicolasstucki @bracevac I moved the check to Typer and tried to type the key as an Ident as discussed: ca5f467. However Symbol.setter is still not defined. Maybe it only is once the whole class is type-checked?

I then tried to type the whole thing as Assign, with a temporary context: dd22105. It seems to work locally, let's see what the CI says.

[SethTisue]

I hit this issue in my own code just this morning, during a 3.6.1 upgrade — locating the cause took me a while, so I’m glad to see a warning being added

[noti0na1]

Can you add a test for #21770 as well?

def f(g: Int  => Unit) = g(0)

def test = 
  var cache: Option[Int] = None
  f(i => (cache = Some(i)))

Thanks!

[mbovel]

Can you add a test for #21770 as well?

Done.

[noti0na1]

LGTM