Annotation with default arguments result in warning

[scabug]

Using annotation with default arguments sometimes causing a unnecessary warning. Order of parameters is same for usage and declaration so this is not caused by #7656. Tested on both 2.11.6 and 2.11.7.

Here is minimal[1]:

class Ann(a: Int = 1, b: Int = 2, c: Int = 4) extends StaticAnnotation

@Ann() class TestAnn1 // no warning
@Ann(a = 1) class TestAnn2 // no warning
@Ann(a = 2, b = 1) class TestAnn3 // no warning
@Ann(a = 2, b = 1, c = 1) class TestAnn4 // no warning
@Ann(b = 1) class TestAnn5 // warning
@Ann(b = 1, c = 1) class TestAnn6 // warning
@Ann( c = 1) class TestAnn7 // warning

[1] https://gist.github.com/romanowski/aa495710f86c4185b525

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9612?orig=1
Reporter: @romanowski
See #7656

[scabug]

@romanowski said:
To overcome this we are currently using compiler plugin to workaround this issue but we cannot do that in Intellij presentation compiler. We are using fatal warning so ignoring this warning is not an option.

[scabug]

@som-snytt said:
@Ann(b = 1) class TestAnn5 becomes @Ann(b = 1, a = default$1, c = default$3) class TestAnn5 which is why it looks out of order.

[scabug]

@soc said:
I need to check whether scala/scala#4848 caused any improvements/regressions.