Refutable extractor may be an Apply tree

And in fact we need to be able to handle arbitrary parameter lists (and type
parameter lists) when extracting the extractor name.

Fixes scala#15650

Author: griggt

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

@@ -816,10 +816,13 @@ trait Checking {
         case RefutableExtractor =>
           val extractor =
             val UnApply(fn, _, _) = pat: @unchecked
-            fn match
+            tpd.funPart(fn) match
               case Select(id, _) => id
-              case TypeApply(Select(id, _), _) => id
-          em"pattern binding uses refutable extractor `$extractor`"
+              case _ => EmptyTree
+          if extractor.isEmpty then
+            em"pattern binding uses refutable extractor"
+          else
+            em"pattern binding uses refutable extractor `$extractor`"
 
       val fix =
         if isPatDef then "adding `: @unchecked` after the expression"

tests/pos/i15650.scala

@@ -0,0 +1,18 @@
+class Rational
+
+import scala.quoted.*
+
+class TC
+
+object meta:
+  object rationalTE:
+    def unapply(using Quotes)(tr: quotes.reflect.TypeRepr): Option[Rational] = ???
+
+  object rationalTC:
+    def unapply(using Quotes)(using TC)(tr: quotes.reflect.TypeRepr): Option[Rational] = ???
+
+  def foo(using Quotes)(p: quotes.reflect.TypeRepr): Unit =
+    val rationalTE(e) = p  // warn: pattern binding uses refutable extractor `meta.rationalTE`
+
+  def bar(using Quotes)(using TC)(p: quotes.reflect.TypeRepr): Unit =
+    val rationalTC(c) = p  // warn: pattern binding uses refutable extractor `meta.rationalTC`