Add reflect Unapply.apply

Fixes scala#12850

Author: nicolasstucki

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -1439,6 +1439,8 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
     end UnapplyTypeTest
 
     object Unapply extends UnapplyModule:
+      def apply(fun: Term, implicits: List[Term], patterns: List[Tree]): Unapply =
+        withDefaultPos(tpd.UnApply(fun, implicits, patterns, dotc.core.Symbols.defn.NothingType))
       def copy(original: Tree)(fun: Term, implicits: List[Term], patterns: List[Tree]): Unapply =
         withDefaultPos(tpd.cpy.UnApply(original)(fun, implicits, patterns))
       def unapply(x: Unapply): (Term, List[Term], List[Tree]) =

library/src/scala/quoted/Quotes.scala

@@ -2087,7 +2087,11 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
 
     /** Methods of the module object `val Unapply` */
     trait UnapplyModule { this: Unapply.type =>
+      /** Create an `Unapply` tree representing a pattern `<fun>(<patterns*>)(using <implicits*>)` */
+      def apply(fun: Term, implicits: List[Term], patterns: List[Tree]): Unapply
+      /** Copy an `Unapply` tree representing a pattern `<fun>(<patterns*>)(using <implicits*>)` */
       def copy(original: Tree)(fun: Term, implicits: List[Term], patterns: List[Tree]): Unapply
+      /** Matches an `Unapply(fun, implicits, patterns)` tree representing a pattern `<fun>(<patterns*>)(using <implicits*>)` */
       def unapply(x: Unapply): (Term, List[Term], List[Tree])
     }
 
@@ -2097,8 +2101,15 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Extension methods of `Unapply` */
     trait UnapplyMethods:
       extension (self: Unapply)
+        /** The extractor function of the pattern.
+         *
+         *  It may be a reference to the `unapply` method of the pattern or may be a
+         *  partially applied tree containing type parameters and leading given parameters.
+         */
         def fun: Term
+        /** Training implicit parameters of the `unapply` method */
         def implicits: List[Term]
+        /** List of nested patterns */
         def patterns: List[Tree]
       end extension
     end UnapplyMethods

project/MiMaFilters.scala

@@ -11,5 +11,7 @@ object MiMaFilters {
     exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SourceFileMethods.getJPath"),
     exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SourceFileMethods.name"),
     exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SourceFileMethods.path"),
+    exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#UnapplyModule.apply"),
+    exclude[DirectMissingMethodProblem]("scala.quoted.Quotes#reflectModule#UnapplyModule.apply"),
   )
 }

tests/pos-macros/i12850/Macros_1.scala

@@ -0,0 +1,19 @@
+
+import scala.quoted.*
+
+inline def foo() = ${ expr }
+
+private def expr(using Quotes): Expr[Unit] =
+  import quotes.reflect.*
+
+  // Option(1) match
+  //   case Some(1) => ()
+  //   case None => ()
+  val mtch2 = Match(
+      Apply(TypeApply(Ref(Symbol.requiredMethod("scala.Option.apply")), List(Inferred(TypeRepr.of[Int]))), List(Literal(IntConstant(1)))),
+      List(
+        CaseDef(/** FIXME: needs TypedTree from #12200; remove cast */Typed(Unapply(TypeApply(Ref(Symbol.requiredMethod("scala.Some.unapply")), List(Inferred(TypeRepr.of[Int]))), Nil, List(Literal(IntConstant(1)))).asInstanceOf[Term], Inferred(TypeRepr.of[Some[Int]])), None, Literal(UnitConstant())),
+        CaseDef(Ref(Symbol.requiredModule("scala.None")), None, Literal(UnitConstant())))
+  )
+
+  mtch2.asExprOf[Unit]

tests/pos-macros/i12850/Test_2.scala

@@ -0,0 +1 @@
+def test = foo()