Deprecate +(x: String): String on primitives

[smarter]

This is consistent with the deprecation of any2stringadd in #6315.

[smarter]

Somehow this broke specialization of Function:

> scalac test/files/run/Course-2002-02.scala
> scala Test
[...]
java.lang.NoSuchMethodError: scala.Function2.apply$mcDII$sp(II)D
        at M4$.<init>(Course-2002-02.scala:106)
        at M4$.<clinit>(Course-2002-02.scala)
        at Test$.main(Course-2002-02.scala:533)
        at Test.main(Course-2002-02.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at scala.reflect.internal.util.ScalaClassLoader.$anonfun$run$2(ScalaClassLoader.scala:99)
        at scala.reflect.internal.util.ScalaClassLoader.asContext(ScalaClassLoader.scala:33)
        at scala.reflect.internal.util.ScalaClassLoader.asContext$(ScalaClassLoader.scala:31)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:130)
        at scala.reflect.internal.util.ScalaClassLoader.run(ScalaClassLoader.scala:99)
        at scala.reflect.internal.util.ScalaClassLoader.run$(ScalaClassLoader.scala:91)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:130)
        at scala.tools.nsc.CommonRunner.run(ObjectRunner.scala:22)
        at scala.tools.nsc.CommonRunner.run$(ObjectRunner.scala:21)
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
        at scala.tools.nsc.CommonRunner.runAndCatch(ObjectRunner.scala:29)
        at scala.tools.nsc.CommonRunner.runAndCatch$(ObjectRunner.scala:28)
        at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:63)
        at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:83)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:94)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:99)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

I don't have the faintest idea why. Any clue?

[smarter]

Somehow this broke specialization of Function

Looks like it works on the CI and also works locally after doing a clean ¯\_(ツ)_/¯

[lrytz]

Nice, thank you!

[dwijnand]

Nice work.

[Jasper-M]

Next up: changing + on String to only accept a String?

[lrytz]

A few more tests to update: https://scala-ci.typesafe.com/job/scala-2.13.x-validate-main/2377/#showFailuresLink

[lrytz]

That was actually an addition 🤣

Done.

[xuwei-k]

scala/bug#11025

[nafg]

Should this have a release notes label like #6315 ?

[nafg]

I'm not sure I get the point of this. An overbroad method on Any is one thing. What are some pitfalls that removing it from primitives avoids?

[Ichoran]

@nafg - It avoids strings gobbling up every other type when you didn't intend it. Normally this wouldn't be an issue because the type would be wrong and it'd be caught soon enough downstream, but if you end up wanting a string at the end anyway (because it's output), you can end up in a situation where you meant to do some math and report on the outcome, but instead you concatenated a number with something. (I have actually done this.)

It also reduces the number of confusing "Why does it say I can't have a String here?! I don't! (Do I?)" episodes.