`AnonymousInstanceCannotBeEmpty` error not triggered

[WojciechMazur]

Anonymous givens should not be allowed. There is a dedicated error code for this

scala3/compiler/src/dotty/tools/dotc/reporting/messages.scala

Lines 2877 to 2884 in f310b11

	class AnonymousInstanceCannotBeEmpty(impl: untpd.Template)(using Context)
	extends SyntaxMsg(AnonymousInstanceCannotBeEmptyID) {
	def msg(using Context) = i"anonymous instance must implement a type or have at least one extension method"
	def explain(using Context) =
	i"""|Anonymous instances cannot be defined with an empty body. The block
	|`${impl.show}` should either contain an implemented type or at least one extension method.
	|"""
	}

However it seems to be never triggered in

scala3/compiler/src/dotty/tools/dotc/ast/Desugar.scala

Lines 1349 to 1361 in f310b11

	/** Invent a name for an anonymous given of type or template `impl`. */
	def inventGivenName(impl: Tree)(using Context): SimpleName =
	val str = impl match
	case impl: Template =>
	if impl.parents.isEmpty then
	report.error(AnonymousInstanceCannotBeEmpty(impl), impl.srcPos)
	nme.ERROR.toString
	else
	impl.parents.map(inventTypeName(_)).mkString("given_", "_", "")
	case impl: Tree =>
	"given_" ++ inventTypeName(impl)
	str.toTermName.asSimpleName

Compiler version

3.7.4
3.8.1-nightly

Minimized code

given {}

The question is should anonymous refinements be allowed:

given {def foo: Int} = ???
given {def bar: Int} = ???

Both compile but produce the same name leading to other compilation error

Output

Compiles

Expectation