fix: match completions for type aliases (#18667)

metals backport:  scalameta/metals#5714
CC: @tgodzik

Author: tgodzik

presentation-compiler/src/main/dotty/tools/pc/completions/MatchCaseCompletions.scala

@@ -90,7 +90,7 @@ object CaseKeywordCompletion:
             new Parents(NoType, definitions)
       case sel => new Parents(sel.tpe, definitions)
 
-    val selectorSym = parents.selector.typeSymbol
+    val selectorSym = parents.selector.widen.metalsDealias.typeSymbol
 
     // Special handle case when selector is a tuple or `FunctionN`.
     if definitions.isTupleClass(selectorSym) || definitions.isFunctionClass(
@@ -153,7 +153,9 @@ object CaseKeywordCompletion:
           if isValid(ts) then visit(autoImportsGen.inferSymbolImport(ts))
         )
       // Step 2: walk through known subclasses of sealed types.
-      val sealedDescs = subclassesForType(parents.selector.widen.bounds.hi)
+      val sealedDescs = subclassesForType(
+        parents.selector.widen.metalsDealias.bounds.hi
+      )
       sealedDescs.foreach { sym =>
         val symbolImport = autoImportsGen.inferSymbolImport(sym)
         visit(symbolImport)
@@ -241,7 +243,7 @@ object CaseKeywordCompletion:
       completionPos,
       clientSupportsSnippets
     )
-    val tpe = selector.tpe.widen.bounds.hi match
+    val tpe = selector.tpe.widen.metalsDealias.bounds.hi match
       case tr @ TypeRef(_, _) => tr.underlying
       case t => t
 

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionCaseSuite.scala

@@ -657,3 +657,44 @@ class CompletionCaseSuite extends BaseCompletionSuite:
          |case Singing(song) => test.Activity
          |case Sports(time, intensity) => test.Activity""".stripMargin
     )
+
+  @Test def `type-alias-case` =
+    check(
+      s"""|object O:
+          |  type Id[A] = A
+          |
+          |  enum Animal:
+          |    case Cat, Dog
+          |
+          |  val animal: Id[Animal] = ???
+          |
+          |  animal match
+          |    cas@@
+          |""".stripMargin,
+      """|case Animal.Cat =>
+         |case Animal.Dog =>
+         |""".stripMargin,
+    )
+
+  @Test def `type-alias-sealed-trait-case` =
+    check(
+      s"""|object O {
+          | type Id[A] = A
+          |
+          |sealed trait Animal
+          |object Animal {
+          |   case class Cat() extends Animal
+          |   case object Dog extends Animal
+          |}
+          |
+          | val animal: Id[Animal] = ???
+          |
+          |  animal match {
+          |    cas@@
+          |  }
+          |}
+          |""".stripMargin,
+      """|case Cat() => test.O.Animal
+         |case Dog => test.O.Animal
+         |""".stripMargin,
+    )

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionMatchSuite.scala

@@ -601,3 +601,72 @@ class CompletionMatchSuite extends BaseCompletionSuite:
           |}""".stripMargin,
       filter = _.contains("exhaustive")
     )
+
+  @Test def `type-alias` =
+    checkEdit(
+      s"""|object O {
+          | type Id[A] = A
+          |
+          | enum Animal:
+          |   case Cat, Dog
+          |
+          | val animal: Id[Animal] = ???
+          |
+          | animal ma@@
+          |}
+          |""".stripMargin,
+      s"""object O {
+          | type Id[A] = A
+          |
+          | enum Animal:
+          |   case Cat, Dog
+          |
+          | val animal: Id[Animal] = ???
+          |
+          | animal match
+          |\tcase Animal.Cat => $$0
+          |\tcase Animal.Dog =>
+          |
+          |}
+          |""".stripMargin,
+      filter = _.contains("exhaustive"),
+    )
+
+  @Test def `type-alias-sealed-trait` =
+    checkEdit(
+      s"""|object O {
+          | type Id[A] = A
+          |
+          |sealed trait Animal
+          |object Animal {
+          |   case object Cat extends Animal
+          |   case object Dog extends Animal
+          |}
+          |
+          | val animal: Id[Animal] = ???
+          |
+          |animal ma@@
+          |}
+          |""".stripMargin,
+      s"""|
+          |import O.Animal.Cat
+          |import O.Animal.Dog
+          |object O {
+          | type Id[A] = A
+          |
+          |sealed trait Animal
+          |object Animal {
+          |   case object Cat extends Animal
+          |   case object Dog extends Animal
+          |}
+          |
+          | val animal: Id[Animal] = ???
+          |
+          |animal match
+          |\tcase Cat => $$0
+          |\tcase Dog =>
+          |
+          |}
+          |""".stripMargin,
+      filter = _.contains("exhaustive"),
+    )