Strip named tuple from scrutinee when testing refutability of a named pattern match

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -387,8 +387,8 @@ object TypeOps:
           if tycon1.typeSymbol == tycon2.typeSymbol && (tycon1 =:= tycon2) =>
             mergeRefinedOrApplied(tp1, tp2) match
               case tp: AppliedType if tp.isUnreducibleWild =>
-                // fall back to or-dominators rather tahn inferring a type that would
-                // caue an unreducible type error later.
+                // fall back to or-dominators rather than inferring a type that would
+                // cause an unreducible type error later.
                 approximateOr(tp1, tp2)
               case tp => tp
           case (tp1, tp2) =>

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

@@ -963,10 +963,16 @@ trait Checking {
       false
     }
 
-    def check(pat: Tree, pt: Type): Boolean =
+    // Is scrutinee type `pt` a subtype of `pat.tpe`, after stripping named tuples
+    // and accounting for large generic tuples?
+    // Named tuples need to be stripped off, since names are dropped in patterns
+    def conforms(pat: Tree, pt: Type): Boolean =
       pt.isTupleXXLExtract(pat.tpe) // See isTupleXXLExtract, fixes TupleXXL parameter type
-      || pt <:< pat.tpe
-      || fail(pat, pt, Reason.NonConforming)
+      || pt.stripNamedTuple <:< pat.tpe
+      || (pt.widen ne pt) && conforms(pat, pt.widen)
+
+    def check(pat: Tree, pt: Type): Boolean =
+      conforms(pat, pt) || fail(pat, pt, Reason.NonConforming)
 
     def recur(pat: Tree, pt: Type): Boolean =
       !sourceVersion.isAtLeast(`3.2`)