Implicits are resolved with empty parameter lists

[hamzaremmal]

Compiler version

Since 3.4.2

Minimized code

implicit val x: Int = 0
def foo(implicit x: Int): Int = x
foo()

Output

Complies

Expectation

Behaves as Scala < 3.4.2 and as in the specification.

Note

This is the error message that was generated before 3.4.2

-- [E171] Type Error: ----------------------------------------------------------
1 |foo()
  |^^^^^
  |missing argument for parameter x of method foo: (implicit x: Int): Int
1 error found

and in scala 2.13.14

scala> foo()
          ^
       error: not enough arguments for method foo: (implicit x: Int): Int.
       Unspecified value parameter x.

[Gedochao]

Last good stable release: 3.4.1
Last good nightly release: 3.4.2-RC1-bin-20240222-98efdab-NIGHTLY
First bad nightly release: 3.4.2-RC1-bin-20240226-e0cb1e7-NIGHTLY
First bad stable release: 3.4.2

e0cb1e7 is the first bad commit
cc @SethTisue

[Gedochao]

Looks similar to:

• Possibly incorrect suppression of parameter list #22380

Potentially also relevant:

• Overloading and implicit argument result in inconsistent outcomes #22421
• Overloading or implicit bug in 3.4.1 #20053
• Overloading with context function bug #15163

[sjrd]

e0cb1e7 is the first bad commit
cc @SethTisue

That ... does not look likely. 😅 Is it possible that bisect ended up in a "local minimum" of the build not even functioning at all, rather than the actual typechecking regression?

[som-snytt]

Seems to be 1e89016

A quarter-line tweak in #19737

[Gedochao]

Is it possible that bisect ended up in a "local minimum" of the build not even functioning at all, rather than the actual typechecking regression?

Yeah... that's likely what happened 😅 I need to think about tweaking the bisect script for cases such as this...

Anyway, as @som-snytt suggested, the correct commit seems to be 1e89016
cc @EugeneFlesselle

[SethTisue]

whew

[som-snytt]

I took a look. It turns on that an implicit parameter list is supplied only when it is missing, whereas with "use-site using" or explicit using you can supply just some args. (In matchArgs, it already has an arg list.) (I remember that subtlety came up a few years ago in documentation for scala 2.)

All this time, I thought I knew how to call a method.

I'll submit a PR when I see where to toss the monkey wrench.