Address review: warning on insertion

Author: liufengyun

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3268,7 +3268,15 @@ class Typer extends Namer
 
     def adaptNoArgsOther(wtp: Type, functionExpected: Boolean): Tree = {
       val implicitFun = isImplicitFunctionRef(wtp) && !untpd.isContextualClosure(tree)
-      def caseCompanion = functionExpected && tree.symbol.is(Module) && tree.symbol.companionClass.is(Case)
+      def caseCompanion =
+          functionExpected &&
+          tree.symbol.is(Module) &&
+          tree.symbol.companionClass.is(Case) &&
+          !tree.tpe.widen.classSymbol.asClass.classParents.exists(defn.isFunctionType(_)) && {
+            ctx.warning("The method `apply` is inserted. The auto insertion will be deprecated, please write `" + tree.show + ".apply` explicitly.", tree.sourcePos)
+            true
+          }
+
       if ((implicitFun || caseCompanion) &&
           !isApplyProto(pt) &&
           pt != AssignProto &&

tests/neg-custom-args/fatal-warnings/i6190a.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg-custom-args/fatal-warnings/i6190b.scala:3:29 -------------------------------------------------------
+3 |def foo = List("1", "2").map(Rule)  // error
+  |                             ^^^^
+  |      The method `apply` is inserted. The auto insertion will be deprecated, please write `Rule.apply` explicitly.

tests/neg-custom-args/fatal-warnings/i6190b.check

@@ -0,0 +1,3 @@
+case class Rule(name: String)
+
+def foo = List("1", "2").map(Rule)  // error

tests/neg-custom-args/fatal-warnings/i6190b.scala

@@ -0,0 +1,6 @@
+class Rule(name: String)
+object Rule {
+  def apply(name: String): Rule = new Rule(name)
+}
+
+def foo = List("1", "2").map(Rule)  // error

tests/neg/i6190.scala

@@ -0,0 +1,6 @@
+case class Rule(name: String)
+object Rule extends (String => Rule) {
+  def apply(name: String): Rule = new Rule(name)
+}
+
+def foo = List("1", "2").map(Rule)

tests/pos-special/fatal-warnings/i6190a.scala

@@ -0,0 +1,3 @@
+case class Rule(name: String)
+
+def foo = List("1", "2").map(Rule.apply)