Import selector checks looks at left of arrow instead of right

[som-snytt]

Compiler version

3.3.2-RC1-bin-SNAPSHOT-git-8948092

Minimized code

➜  ~ ~/projects/dotty/bin/scala
Welcome to Scala 3.3.2-RC1-bin-SNAPSHOT-git-8948092 (20.0.1, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> object O { val a = 1 }
// defined object O

scala> import O.{a=>b, a}
-- [E122] Syntax Error: ------------------------------------------------------------------------------------------------
1 |import O.{a=>b, a}
  |                ^
  |                a is renamed twice on the same import line.
1 error found

scala> import O.{a=>b, toString=>b}

scala>

Output

// as shown

Expectation

The aliasing import is fine, but introducing the same name twice is not.

The spec does not constrain import selectors, so technically any warning or error is a lint.

scala/bug#12813