Nobody expects to import toString

[som-snytt]

Compiler version

3.6.3

Minimized code

scala> def f = { import scala.util.Properties.*; toString }
-- [E049] Reference Error: -----------------------------------------------------
1 |def f = { import scala.util.Properties.*; toString }
  |                                          ^^^^^^^^
  |               Reference to toString is ambiguous.
  |               It is both defined in object rs$line$1
  |               and imported subsequently by import scala.util.Properties._
  |
  | longer explanation available when compiling with `-explain`
1 error found

Output

[error] 594 |      println(s"ARG $toString")
[error]     |                     ^^^^^^^^
[error]     |           Reference to toString is ambiguous.
[error]     |           It is both defined in class Test
[error]     |           and imported subsequently by import scala.util.Properties._

Expectation

When I'm really frazzled and trying to debug, don't mess with me, just print the string.

The example is from vulpix, where the local import was 100 lines earlier in the source.

This came up in Scala 2 implementation of the ambiguity for inherited vs definitions in scope. That was at scala/scala#10220 (comment) where an exception for toString was deemed too special.

Scala 2 disallows importing universal members from root imports. There is a ticket for package object members referenced by top level defs.

So there is precedent for placing limits on these behaviors which sacrifice convenience and intuition to regularity.

In a template nesting level, an import is shadowed by an inherited member, but a local import wins.

A possible limit would be to always disallow import of universal members by wildcard import (including root imports).

(Whether to detune the ambiguity for inherited vs scope is a separate issue, but worth considering.)

[Gedochao]

Note: this currently causes a warning when done outside of the REPL.

def f = { import scala.util.Properties.*; toString }

scala-cli compile repro.scala --server=false
-- [E181] Potential Issue Warning: /Users/pchabelski/IdeaProjects/scala-cli-tests-2/untitled/compiler-repro/repro.scala:1:42 
1 |def f = { import scala.util.Properties.*; toString }
  |                                          ^^^^^^^^
  |                         Suspicious top-level unqualified call to toString
  |
  | longer explanation available when compiling with `-explain`
1 warning found

[som-snytt]

That's funny. The top-level warning is supposed to warn that you're using toString of a package object, which isn't the case here.

I don't know why it doesn't error in a top-level def.

class C:
  def f =
    import java.util.Properties.*
    toString // error typer

def g =
  import java.util.Properties.*
  toString // warn refchecks