Dotty: Regression Aug 15th-17th in community build compiling Squants

[olafurpg]

• 0.3.0-bin-20170815-8b8baba-NIGHTLY is green https://travis-ci.org/lampepfl/dotty-community-build/jobs/265491127
• 0.3.0-bin-20170817-fed2dc2-NIGHTLY is red https://travis-ci.org/lampepfl/dotty-community-build/jobs/265885027#L588

Compilation errors

[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/energy/Energy.scala:242:19 
[error] 242 |    def toEnergy = Energy(s)
[error]     |                   ^^^^^^
[error]     |              object Energy in package energy does not take parameters
[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/energy/Power.scala:145:18 
[error] 145 |    def toPower = Power(s)
[error]     |                  ^^^^^
[error]     |               object Power in package energy does not take parameters
[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/energy/PowerRamp.scala:109:22 
[error] 109 |    def toPowerRamp = PowerRamp(s)
[error]     |                      ^^^^^^^^^
[error]     |           object PowerRamp in package energy does not take parameters
[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/information/Information.scala:214:24 0m
[error] 214 |    def toInformation = Information(s)
[error]     |                        ^^^^^^^^^^^
[error]     |    object Information in package information does not take parameters
[warn] -- Migration Warning: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/market/Money.scala:465:27 
[warn] 465 |    def negate(x: Money) = -x
[warn]     |                           ^^
[warn]     |                 method unary_- in class Quantity requires () argument
[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/mass/Mass.scala:216:17 
[error] 216 |    def toMass = Mass(s)
[error]     |                 ^^^^
[error]     |                 object Mass in package mass does not take parameters
[error] -- [E049] Reference Error: /home/travis/build/lampepfl/dotty-community-build/squants/shared/src/main/scala/squants/space/Length.scala:290:19 
[error] 290 |    def toLength = Length(s)
[error]     |                   ^^^^^^
[error]     |               object Length in package space does not take parameters
[warn] 5 warnings found
[error] 6 errors found
[error] (squantsJVM/compile:compileIncremental) Compilation failed

Definition of Energy https://github.com/dotty-staging/squants/blob/616fe0d74bedea35a5b2f0e79dc3c42cbaa5b0ce/shared/src/main/scala/squants/energy/Energy.scala#L27

[smarter]

My guess would be https://github.com/lampepfl/dotty/pull/2962

[felixmulder]

Minimized:

object Test {
  object Energy {
    private def parse(value: Any) = ???
    def apply = parse _
  }

  // Energy.apply("") // works!
  Energy("") // crashy-boom-boom
}

[smarter]

Felix's reduction is incorrect because it doesn't compile with scalac either.

[felixmulder]

Here's the corrected version, I'm hoping github mail works - because we
can't access the web ui from EPFL currently.

object Test {

  object Energy {
    def apply(load: Int): Int = load
    private def parse(value: Any) = ???
    def apply = parse _
  }

  Energy("")
}

[olafurpg]

Any update on this? The community build is still red for Squants. https://travis-ci.org/lampepfl/dotty-community-build/jobs/270746972#L588

[felixmulder]

We concluded that the code is bad and that it should be changed. What happens is that the call Energy("") has to be adapted with an apply. The problem then becomes, how many applys and where?

So it tries:

Energy.apply(""), but that is not legal since we're actually getting back the function apply which in turn has to be adapted, and #2962 makes that an impossibility.

The code should be changed to: def apply(a: Any) = parse(a) in Squants.

Sorry for the delayed response,
F

[olafurpg]

Fair enough, I agree with the conclusion 👍

[felixmulder]

We should put this in the spec, though :)

[allanrenucci]

I am reopening this issue. The following code snippet is rejected by Dotty but with an unrelated error message:

object Test {
  object Energy {
    private def parse(value: Any) = ???
    def apply = parse _
  }

  Energy("")
}

-- [E043] Syntax Error: tests/allan/Test.scala:23:2 ----------------------------
23 |  Energy("")
   |  ^^^^^^
   |  overloaded or recursive method Energy needs return type

[smarter]

I think the culprit is https://github.com/lampepfl/dotty/pull/2823/commits/30ac9e2fdda6fddadaf42284cc45fef4272c51c2#diff-7c63b7bfffa9340fb48ac9b61fa56beeR1931, some conditions were added to check if we're in an overloaded or recursive method call but I don't understand what they're based on. We could revert to the previous logic here.

[odersky]

I think the culprit is 30ac9e2#diff-7c63b7bfffa9340fb48ac9b61fa56beeR1931

I would guess the same. Allan can you revert that commit and see whether it passes?