Deprecate typesafe variadic class arguments

[dkorpel]

Testing it as an error first to see if anything on buildkite relies on this feature.

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Testing this PR locally

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[dkorpel]

2 buildkite projects fail when it becomes an error:

ddox:

[main(----) INF] Generating module: test
+ '[' '!' -f .no_diff ']'
+ git --no-pager diff --exit-code -- docs
+ popd
~/rejectedsoftware-ddox
+ for dir in tests/*
+ pushd tests/issue177_variadic
~/rejectedsoftware-ddox/tests/issue177_variadic ~/rejectedsoftware-ddox
+ dmd -Xftest.json -Dd__dummy_html -c -o- test.d
test.d(19): Error: cannot have typesafe variadic parameter of class type `test.C`
void bug(scope C c...)
     ^
test.d(40): Error: cannot have typesafe variadic parameter of class type `test.C`
alias FT3 = void function(scope C c...);
^
test.d(55): Error: cannot have typesafe variadic parameter of class type `test.C`
void function(scope C c...) var3;

This is simply a test case for all kinds of typesafe variadic functions, easily removed.

dwt:

    Starting Performing "debug" build using /buildkite/builds/zaphod-4/dlang/dmd/buildkite-ci-build/distribution/bin/dmd for x86_64.
    Building dwt ~master: building configuration [linux-gtk]
base/src/java/lang/Class.d(42,17): Error: cannot have typesafe variadic parameter of class type `java.lang.Class.Class`
    Constructor getConstructor(Class parameterTypes...){
                ^
base/src/java/lang/Class.d(54,17): Error: cannot have typesafe variadic parameter of class type `java.lang.Class.Class`
    Constructor getDeclaredConstructor(Class parameterTypes...){
                ^
base/src/java/lang/Class.d(70,12): Error: cannot have typesafe variadic parameter of class type `java.lang.Class.Class`
    Method getDeclaredMethod(String name, Class parameterTypes...){
           ^
Error /buildkite/builds/zaphod-4/dlang/dmd/buildkite-ci-build/distribution/bin/dmd failed with exit code 1.

These 3 functions are stubs in root class Class that call implMissing, and are never overridden as far as I can see. Considering Class doesn't even have any fields, it's probably a typo, and meant to say Class[] parameterTypes....

[thewilsonator]

This otherwise looks good

[dkorpel]

Walter and Atila approved this in an email, but Walter requested to not break code and keep it as legacy feature, so I removed the comment to make it an error in 2.121.

[Herringway]

If there's no plans to remove it, then call it what it is. A warning.

[dkorpel]

There used to be a -wo switch warning about obsolete features, but it has been superseded by editions. The DIP for that still needs to reach formal assessment, so currently there's no 'correct' way to mark this feature. Considering only 1 (accidental, stub) use is found on buildkite, I don't think it matters here.

[Herringway]

There used to be a -wo switch warning about obsolete features, but it has been superseded by editions. The DIP for that still needs to reach formal assessment, so currently there's no 'correct' way to mark this feature. Considering only 1 (accidental, stub) use is found on buildkite, I don't think it matters here.

The correct way is an error or nothing at all. Editions don't exist, and therefore should not factor into this decision.

[dkorpel]

I'm in favor of turning it into an error, maybe Walter changes his mind 10 releases later.