Support implicit arguments before extractor method

Author: EnzeXing

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -1298,9 +1298,13 @@ object Objects:
           case select: Select =>
             eval(select.qualifier, thisV, klass)
 
-        val implicitValues = evalArgs(implicits.map(Arg.apply), thisV, klass)
-        // TODO: implicit values may appear before and/or after the scrutinee parameter.
-        val unapplyRes = call(receiver, funRef.symbol, TraceValue(scrutinee, summon[Trace]) :: implicitValues, funRef.prefix, superType = NoType, needResolve = true)
+        def implicitValuesBeforeScrutinee(fun: Tree): Contextual[List[ArgInfo]] = fun match
+          case Apply(f, implicitArgs) =>
+            implicitValuesBeforeScrutinee(f) ++ evalArgs(implicitArgs.map(Arg.apply), thisV, klass)
+          case _ => List()
+
+        val implicitValuesAfterScrtinee = evalArgs(implicits.map(Arg.apply), thisV, klass)
+        val unapplyRes = call(receiver, funRef.symbol, TraceValue(scrutinee, summon[Trace]) :: (implicitValuesBeforeScrutinee(fun) ++ implicitValuesAfterScrtinee), funRef.prefix, superType = NoType, needResolve = true)
 
         if fun.symbol.name == nme.unapplySeq then
           var resultTp = unapplyResTp

tests/init-global/neg/unapply-implicit-arg.scala

@@ -0,0 +1,11 @@
+class Foo
+
+object Bar {
+  def unapply(using Foo)(pair: (Int, Int))(using Foo): Option[Int] =
+    if pair._1 == 0 then Some(pair._1) else Some(pair._2)
+  given Foo = new Foo
+  val i1: Int = 0
+  val i2: Int = (i1, i2) match // error
+    case Bar(i) => i
+    case _ => 0
+}

tests/init-global/neg/unapplySeq-implicit-arg.scala

@@ -0,0 +1,11 @@
+class Foo
+
+object Bar {
+  def unapplySeq(using Foo)(using Foo)(pair: (Int, Int))(using Foo): Option[Seq[Int]] =
+    if pair._1 == 0 then Some(Seq(pair._1)) else Some(Seq(pair._2))
+  given Foo = new Foo
+  val i1: Int = 0
+  val i2: Int = (i1, i2) match // error
+    case Bar(i) => i
+    case _ => 0
+}

tests/init-global/pos/unapply-implicit-arg-pos.scala

@@ -0,0 +1,11 @@
+class Foo
+
+object Bar {
+  def unapply(using Foo)(using Foo)(pair: (Int, Int))(using Foo): Option[Int] =
+    if pair._1 == 0 then Some(pair._1) else Some(pair._2)
+  given Foo = new Foo
+  val i1: Int = 0
+  val i2: Int = (i1, i1) match
+    case Bar(i) => i
+    case _ => 0
+}

tests/init-global/pos/unapplySeq-implicit-arg-pos.scala

@@ -0,0 +1,11 @@
+class Foo
+
+object Bar {
+  def unapplySeq(using Foo)(using Foo)(pair: (Int, Int))(using Foo): Option[Seq[Int]] =
+    if pair._1 == 0 then Some(Seq(pair._1)) else Some(Seq(pair._2))
+  given Foo = new Foo
+  val i1: Int = 0
+  val i2: Int = (i1, i1) match
+    case Bar(i) => i
+    case _ => 0
+}