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Disallow empty parameter clauses in extension definition #23143

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Merged
merged 1 commit into from
May 13, 2025
Merged

Disallow empty parameter clauses in extension definition #23143

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10 changes: 8 additions & 2 deletions compiler/src/dotty/tools/dotc/parsing/Parsers.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -3673,7 +3673,10 @@ object Parsers {
// begin termParamClause
inParensWithCommas {
if in.token == RPAREN && paramOwner != ParamOwner.ExtensionPrefix && !impliedMods.is(Given)
then Nil
then
if paramOwner.takesOnlyUsingClauses then
syntaxError(em"`using` expected")
Nil
else
val clause =
if paramOwner == ParamOwner.ExtensionPrefix
Expand Down Expand Up @@ -4468,7 +4471,10 @@ object Parsers {
leadParamss += extParams
isUsingClause(extParams)
do ()
leadParamss ++= termParamClauses(ParamOwner.ExtensionFollow, numLeadParams)
// Empty parameter clauses are filtered out. They are already reported as syntax errors and are not
// allowed here.
val extFollowParams = termParamClauses(ParamOwner.ExtensionFollow, numLeadParams).filterNot(_.isEmpty)
leadParamss ++= extFollowParams
if in.isColon then
syntaxError(em"no `:` expected here")
in.nextToken()
Expand Down
3 changes: 3 additions & 0 deletions tests/neg/extensions-can-only-have-using.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
extension(x: Any)() // error
def f = 42
val x = Nil.f
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