Prevent crashes in erroneous cases

Author: KacperFKorban

Diff for: compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1694,16 +1694,18 @@ trait Applications extends Compatibility {
   def typedUnApply(tree: untpd.UnApply, selType: Type)(using Context): UnApply =
     throw new UnsupportedOperationException("cannot type check an UnApply node")
 
-  def typedAppliedConstructorType(tree: untpd.Apply)(using Context) =
-    val Select(New(tpt), _) = tree.fun: @unchecked // Always wrapped in `New`, see `simpleType` in `Parsers`
-    val tree1 = typedExpr(tree)
-    val widenSkolemsMap = new TypeMap:
-      def apply(tp: Type) = mapOver(tp.widenSkolem)
-    val preciseTp = widenSkolemsMap(tree1.tpe)
-    val classTp = typedType(tpt).tpe
-    if !preciseTp.isError && (preciseTp frozen_=:= classTp) then
-      report.warning(PointlessAppliedConstructorType(tpt, tree.args, classTp), tree.srcPos)
-    TypeTree(preciseTp)
+  def typedAppliedConstructorType(tree: untpd.Apply)(using Context) = tree.fun match
+    case Select(New(tpt), _) =>
+      val tree1 = typedExpr(tree)
+      val widenSkolemsMap = new TypeMap:
+        def apply(tp: Type) = mapOver(tp.widenSkolem)
+      val preciseTp = widenSkolemsMap(tree1.tpe)
+      val classTp = typedType(tpt).tpe
+      if !preciseTp.isError && (preciseTp frozen_=:= classTp) then
+        report.warning(PointlessAppliedConstructorType(tpt, tree.args, classTp), tree.srcPos)
+      TypeTree(preciseTp)
+    case _ =>
+      throw TypeError(em"Unexpected applied constructor type: $tree")
 
   /** Is given method reference applicable to argument trees `args`?
    *  @param  resultType   The expected result type of the application

Diff for: tests/neg/context-function-syntax.scala

@@ -1,5 +1,5 @@
 val test =
-  (using x: Int) => x  // error // error
+  (using x: Int) => x  // error // error // error
 
 val f = () ?=> 23 // error
 val g: ContextFunction0[Int] = ??? // ok

Diff for: tests/neg/deptypes.scala

@@ -2,10 +2,10 @@
 
 type Vec[T] = (n: Int) =>> Array[T] // error: not yet implemented
 
-type Matrix[T](m: Int, n: Int) = Vec[Vec[T](n)](m)  // error: not yet implemented
+type Matrix[T](m: Int, n: Int) = Vec[Vec[T](n)](m)  // error // error: not yet implemented
 
-type Tensor2[T](m: Int)(n: Int) = Matrix[T](m, n)   // error: not yet implemented
+type Tensor2[T](m: Int)(n: Int) = Matrix[T](m, n)
 
-val x: Vec[Int](10) = ???  // error: not yet implemented
+val x: Vec[Int](10) = ???
 val n = 10
-type T = Vec[String](n)  // error: not yet implemented
+type T = Vec[String](n)

Diff for: tests/neg/i7751.scala

@@ -1,3 +1,3 @@
 import language.`3.3`
-val a = Some(a=a,)=> // error // error // error // error
+val a = Some(a=a,)=> // error // error // error
 val a = Some(x=y,)=>