Merge pull request #541 from scala/backport-lts-3.3-23618

Backport "Emit an error for quoted pattern type variable after `new`" to 3.3 LTS

Author: tgodzik

compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala

@@ -229,6 +229,10 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case PointlessAppliedConstructorTypeID // errorNumber: 213
   case IllegalContextBoundsID // errorNumber: 214
   case NamedPatternNotApplicableID // errorNumber: 215
+  case UnnecessaryNN // errorNumber: 216
+  case ErasedNotPureID // errorNumber: 217
+  case IllegalErasedDefID // errorNumber: 218
+  case CannotInstantiateQuotedTypeVarID // errorNumber: 219
 
   def errorNumber = ordinal - 1
 

tests/neg-macros/i22616b.check

@@ -0,0 +1,13 @@
+-- [E007] Type Mismatch Error: tests/neg-macros/i22616b.scala:17:18 ----------------------------------------------------
+17 |      case '{ Foo($y: t) } => // error
+   |                  ^^^^^
+   |                  Found:    t
+   |                  Required: String
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E006] Not Found Error: tests/neg-macros/i22616b.scala:18:19 --------------------------------------------------------
+18 |        '{type S = t; ()} // error
+   |                   ^
+   |                   Not found: type t
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg-macros/i22616b.scala

@@ -0,0 +1,22 @@
+// This test illustrates a current limitation of quoted pattern type variables,
+// which has been discussed in https://github.com/scala/scala3/issues/22616#issuecomment-3012534064:
+// These type variables do not have bound in general (see `typedQuotedTypeVar`),
+// so they might not conform to the expected type. Here, `t` does not conform
+// to `String`.
+
+import scala.quoted.{FromExpr, Expr, Quotes}
+
+case class Foo(x: String)
+
+object Macro:
+  inline def myMacro(): Unit =
+    ${ myMacroImpl('{Foo("hello")}) }
+
+  def myMacroImpl(x: Expr[Foo])(using Quotes): Expr[Unit] =
+    x match
+      case '{ Foo($y: t) } => // error
+        '{type S = t; ()} // error
+      case _ =>
+        println("not a foo")
+
+    '{()}

tests/run-macros/i22616c.check

@@ -0,0 +1 @@
+_B_

tests/run-macros/i22616c/Macro_4.scala

@@ -0,0 +1,11 @@
+import scala.quoted.*
+
+object Macro:
+  inline def myMacro[T](): String =
+    ${ myMacroImpl[T]() }
+
+  def myMacroImpl[T: Type]()(using Quotes): Expr[String] =
+    import quotes.reflect.*
+    val myTypeRepr = MyTypeRepr(TypeRepr.of[T])
+    val `caseName`(name) = myTypeRepr.requiredAnnotationValue[caseName]
+    Expr(name)

tests/run-macros/i22616c/MyTypeRepr_3.scala

@@ -0,0 +1,33 @@
+import scala.quoted.*
+
+final class MyTypeRepr(using val quotes: Quotes)(val unwrap: quotes.reflect.TypeRepr) {
+  import quotes.reflect.*
+
+  def getAnnotation(annotTpe: quotes.reflect.Symbol): Option[quotes.reflect.Term] =
+    unwrap.typeSymbol.getAnnotation(annotTpe)
+
+  def optionalAnnotation[Annot: Type]: Option[Expr[Annot]] = {
+    val annotTpe = TypeRepr.of[Annot]
+    val annotFlags = annotTpe.typeSymbol.flags
+
+    if (annotFlags.is(Flags.Abstract) || annotFlags.is(Flags.Trait))
+      report.errorAndAbort(s"Bad annotation type ${annotTpe.show} is abstract")
+
+    this.getAnnotation(annotTpe.typeSymbol) match
+      case Some(tree) if tree.tpe <:< annotTpe => Some(tree.asExprOf[Annot])
+      case _                                   => None
+  }
+
+  def requiredAnnotation[Annot: Type]: Expr[Annot] =
+    optionalAnnotation[Annot].getOrElse(report.errorAndAbort(s"Missing required annotation `${TypeRepr.of[Annot].show}` for `$this`"))
+
+  def optionalAnnotationValue[Annot: {Type, FromExpr}]: Option[Annot] =
+    optionalAnnotation[Annot].map { expr =>
+      expr.value.getOrElse(report.errorAndAbort(s"Found annotation `${TypeRepr.of[Annot].show}` for `$this`, but are unable to extract Expr.value\n${expr.show}"))
+    }
+
+  def requiredAnnotationValue[Annot: {Type, FromExpr}]: Annot = {
+    val expr = requiredAnnotation[Annot]
+    expr.value.getOrElse(report.errorAndAbort(s"Found annotation `${TypeRepr.of[Annot].show}` for `$this`, but are unable to extract Expr.value\n${expr.show}"))
+  }
+}

tests/run-macros/i22616c/SealedTrait3_2.scala

@@ -0,0 +1,8 @@
+sealed trait SealedTrait3[+A, +B]
+object SealedTrait3 {
+  final case class AB1[+B, +A](a: B, b: A) extends SealedTrait3[B, A]
+  final case class AB2[+C, +D](a: C, b: D) extends SealedTrait3[D, C]
+  final case class A[+T](a: T) extends SealedTrait3[T, Nothing]
+  @caseName("_B_") final case class B[+T](b: T) extends SealedTrait3[Nothing, T]
+  case object Neither extends SealedTrait3[Nothing, Nothing]
+}

tests/run-macros/i22616c/Test_5.scala

@@ -0,0 +1,2 @@
+@main def Test =
+  println(Macro.myMacro[SealedTrait3.B[Any]]())

tests/run-macros/i22616c/caseName_1.scala

@@ -0,0 +1,14 @@
+import scala.quoted.*
+
+final case class caseName(name: String) extends scala.annotation.Annotation
+object caseName {
+  // This demonstrates a workaround for issue #22616.
+  given FromExpr[caseName] =
+    new FromExpr[caseName] {
+      override def unapply(x: Expr[caseName])(using Quotes): Option[caseName] =
+        x match {
+          case '{ new `caseName`(${ Expr(name) }) } => Some(caseName(name))
+          case _                                    => println(x.show); None
+        }
+    }
+}