Fail more eagerly when trying to adapt named unapply patterns (#22315)

closes #22192

Author: odersky

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

@@ -109,6 +109,10 @@ object Applications {
     if (isValid) elemTp else NoType
   }
 
+  def namedTupleOrProductTypes(tp: Type)(using Context): List[Type] =
+    if tp.isNamedTupleType then tp.namedTupleElementTypes.map(_(1))
+    else productSelectorTypes(tp, NoSourcePosition)
+
   def productSelectorTypes(tp: Type, errorPos: SrcPos)(using Context): List[Type] = {
     val sels = for (n <- Iterator.from(0)) yield extractorMemberType(tp, nme.selectorName(n), errorPos)
     sels.takeWhile(_.exists).toList
@@ -177,9 +181,14 @@ object Applications {
       else fallback
 
     private def tryAdaptPatternArgs(elems: List[untpd.Tree], pt: Type)(using Context): Option[List[untpd.Tree]] =
-      tryEither[Option[List[untpd.Tree]]]
-        (Some(desugar.adaptPatternArgs(elems, pt)))
-        ((_, _) => None)
+      namedTupleOrProductTypes(pt) match
+        case List(defn.NamedTuple(_, _))=>
+          // if the product types list is a singleton named tuple, autotupling might be applied, so don't fail eagerly
+          tryEither[Option[List[untpd.Tree]]]
+            (Some(desugar.adaptPatternArgs(elems, pt)))
+            ((_, _) => None)
+        case pts =>
+          Some(desugar.adaptPatternArgs(elems, pt))
 
     private def getUnapplySelectors(tp: Type)(using Context): List[Type] =
       // We treat patterns as product elements if
@@ -199,7 +208,7 @@ object Applications {
       else tp :: Nil
 
     private def productUnapplySelectors(tp: Type)(using Context): Option[List[Type]] =
-      if defn.isProductSubType(tp) then
+      if defn.isProductSubType(tp) && args.lengthCompare(productArity(tp)) <= 0 then
         tryAdaptPatternArgs(args, tp) match
           case Some(args1) if isProductMatch(tp, args1.length, pos) =>
             args = args1

tests/neg/i22192.check

@@ -0,0 +1,30 @@
+-- Error: tests/neg/i22192.scala:6:12 ----------------------------------------------------------------------------------
+6 |  case City(iam = n, confused = p) => // error // error
+  |            ^^^^^^^
+  |            No element named `iam` is defined in selector type City
+-- Error: tests/neg/i22192.scala:6:21 ----------------------------------------------------------------------------------
+6 |  case City(iam = n, confused = p) => // error // error
+  |                     ^^^^^^^^^^^^
+  |                     No element named `confused` is defined in selector type City
+-- [E006] Not Found Error: tests/neg/i22192.scala:7:7 ------------------------------------------------------------------
+7 |    s"$n has a population of $p" // error // error
+  |       ^
+  |       Not found: n
+  |
+  | longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg/i22192.scala:7:30 -----------------------------------------------------------------
+7 |    s"$n has a population of $p" // error // error
+  |                              ^
+  |                              Not found: p
+  |
+  | longer explanation available when compiling with `-explain`
+-- Error: tests/neg/i22192.scala:10:12 ---------------------------------------------------------------------------------
+10 |  case Some(iam = n) => // error
+   |            ^^^^^^^
+   |            No element named `iam` is defined in selector type City
+-- [E006] Not Found Error: tests/neg/i22192.scala:11:4 -----------------------------------------------------------------
+11 |    n // error
+   |    ^
+   |    Not found: n
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i22192.scala

@@ -0,0 +1,11 @@
+import scala.language.experimental.namedTuples
+
+case class City(name: String, population: Int)
+
+def getCityInfo(city: City) = city match
+  case City(iam = n, confused = p) => // error // error
+    s"$n has a population of $p" // error // error
+
+def getCityInfo1(city: Option[City]) = city match
+  case Some(iam = n) => // error
+    n // error

tests/neg/i22192a.check

@@ -0,0 +1,20 @@
+-- Error: tests/neg/i22192a.scala:6:12 ---------------------------------------------------------------------------------
+6 |  case Some(iam = n) => // error
+  |            ^^^^^^^
+  |            No element named `iam` is defined in selector type (name : String)
+-- [E006] Not Found Error: tests/neg/i22192a.scala:7:4 -----------------------------------------------------------------
+7 |    n // error
+  |    ^
+  |    Not found: n
+  |
+  | longer explanation available when compiling with `-explain`
+-- Error: tests/neg/i22192a.scala:11:12 --------------------------------------------------------------------------------
+11 |  case Some(iam = n) => // error
+   |            ^^^^^^^
+   |            No element named `iam` is defined in selector type (name : String, population : Int)
+-- [E006] Not Found Error: tests/neg/i22192a.scala:12:4 ----------------------------------------------------------------
+12 |    n // error
+   |    ^
+   |    Not found: n
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i22192a.scala

@@ -0,0 +1,13 @@
+import scala.language.experimental.namedTuples
+
+type City = (name: String)
+
+def getCityInfo(city: Option[City]) = city match
+  case Some(iam = n) => // error
+    n // error
+  case _ =>
+
+def getCiryInfo1(city: Option[(name: String, population: Int)]) = city match
+  case Some(iam = n) => // error
+    n // error
+  case _ =>

tests/pos/i22192.scala

@@ -0,0 +1,15 @@
+import scala.language.experimental.namedTuples
+
+case class City(name: String, population: Int)
+
+def getCityInfo(city: City) = city match
+  case City(population = p, name = n) =>
+    s"$n has a population of $p"
+
+def getCityInfo1(city: Option[(name: String)]) = city match
+  case Some(name = n) => n
+  case _ =>
+
+def getCityInfo2(city: Option[(name: String, population: Int)]) = city match
+  case Some(name = n) => n
+  case _ =>