Backport "Emit an error for quoted pattern type variable after new" to 3.7.3 (#23644)

WojciechMazur · web-flow · commit d8f21026a9e5 · 2025-08-01T19:33:11.000+02:00
Backports #23618 to the 3.7.3-RC1. PR submitted by the release tooling. [skip ci]
diff --git a/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala b/compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala
@@ -232,6 +232,7 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case UnnecessaryNN // errorNumber: 216
   case ErasedNotPureID // errorNumber: 217
   case IllegalErasedDefID // errorNumber: 218
+  case CannotInstantiateQuotedTypeVarID // errorNumber: 219
 
   def errorNumber = ordinal - 1
 
diff --git a/compiler/src/dotty/tools/dotc/reporting/messages.scala b/compiler/src/dotty/tools/dotc/reporting/messages.scala
@@ -3435,6 +3435,18 @@ final class QuotedTypeMissing(tpe: Type)(using Context) extends StagingMessage(Q
 
 end QuotedTypeMissing
 
+final class CannotInstantiateQuotedTypeVar(symbol: Symbol)(using patternCtx: Context) extends StagingMessage(CannotInstantiateQuotedTypeVarID):
+  override protected def msg(using Context): String =
+    i"""Quoted pattern type variable `${symbol.name}` cannot be instantiated.
+      |If you meant to refer to a class named `${symbol.name}`, wrap it in backticks.
+      |If you meant to introduce a binding, this is not allowed after `new`. You might
+      |want to use the lower-level `quotes.reflect` API instead.
+      |Read more about type variables in quoted pattern in the Scala documentation:
+      |https://docs.scala-lang.org/scala3/guides/macros/quotes.html#type-variables-in-quoted-patterns
+    """
+
+  override protected def explain(using Context): String = ""
+
 final class DeprecatedAssignmentSyntax(key: Name, value: untpd.Tree)(using Context) extends SyntaxMsg(DeprecatedAssignmentSyntaxID):
   override protected def msg(using Context): String =
     i"""Deprecated syntax: since 3.7 this is interpreted as a named tuple with one element,
diff --git a/compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala b/compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala
@@ -222,7 +222,7 @@ trait QuotesAndSplices {
         if ctx.mode.is(Mode.InPatternAlternative) then
           report.error(IllegalVariableInPatternAlternative(tree.name), tree.srcPos)
         val typeSym = inContext(quotePatternOuterContext(ctx)) {
-          newSymbol(ctx.owner, tree.name.toTypeName, Case, typeSymInfo, NoSymbol, tree.span)
+          newSymbol(ctx.owner, tree.name.toTypeName, Synthetic | Case, typeSymInfo, NoSymbol, tree.span)
         }
         addQuotedPatternTypeVariable(typeSym)
         Bind(typeSym, untpd.Ident(nme.WILDCARD).withType(typeSymInfo)).withSpan(tree.span)
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1237,6 +1237,9 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       case _ =>
         var tpt1 = typedType(tree.tpt)
         val tsym = tpt1.tpe.underlyingClassRef(refinementOK = false).typeSymbol
+        if ctx.mode.isQuotedPattern && tpt1.tpe.typeSymbol.isAllOf(Synthetic | Case) then
+          val errorTp = errorType(CannotInstantiateQuotedTypeVar(tpt1.tpe.typeSymbol), tpt1.srcPos)
+          return cpy.New(tree)(tpt1).withType(errorTp)
         if tsym.is(Package) then
           report error(em"$tsym cannot be instantiated", tpt1.srcPos)
         tpt1 = tpt1.withType(ensureAccessible(tpt1.tpe, superAccess = false, tpt1.srcPos))
diff --git a/tests/neg-macros/i22616.check b/tests/neg-macros/i22616.check
@@ -0,0 +1,16 @@
+-- [E219] Staging Issue Error: tests/neg-macros/i22616.scala:13:22 -----------------------------------------------------
+13 |          case '{ new caseName(${ Expr(name) }) } => Some(caseName(name))  // error // error
+   |                      ^^^^^^^^
+   |                  Quoted pattern type variable `caseName` cannot be instantiated.
+   |                  If you meant to refer to a class named `caseName`, wrap it in backticks.
+   |                  If you meant to introduce a binding, this is not allowed after `new`. You might
+   |                  want to use the lower-level `quotes.reflect` API instead.
+   |                  Read more about type variables in quoted pattern in the Scala documentation:
+   |                  https://docs.scala-lang.org/scala3/guides/macros/quotes.html#type-variables-in-quoted-patterns
+   |                      
+-- [E006] Not Found Error: tests/neg-macros/i22616.scala:13:67 ---------------------------------------------------------
+13 |          case '{ new caseName(${ Expr(name) }) } => Some(caseName(name))  // error // error
+   |                                                                   ^^^^
+   |                                                                   Not found: name
+   |
+   | longer explanation available when compiling with `-explain`
diff --git a/tests/neg-macros/i22616.scala b/tests/neg-macros/i22616.scala
@@ -0,0 +1,18 @@
+import scala.quoted.*
+
+final case class caseName(name: String) extends scala.annotation.Annotation
+object caseName {
+
+  given FromExpr[caseName] =
+    new FromExpr[caseName] {
+      override def unapply(x: Expr[caseName])(using Quotes): Option[caseName] =
+        val y: Int = 42
+        x match {
+          case '{ caseName(${ Expr(name) }) }     => Some(caseName(name))
+          // with/without the following line...
+          case '{ new caseName(${ Expr(name) }) } => Some(caseName(name))  // error // error
+          case _                                  => println(x.show); None
+        }
+    }
+
+}
diff --git a/tests/neg-macros/i22616b.check b/tests/neg-macros/i22616b.check
@@ -0,0 +1,13 @@
+-- [E007] Type Mismatch Error: tests/neg-macros/i22616b.scala:17:18 ----------------------------------------------------
+17 |      case '{ Foo($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`
diff --git a/tests/neg-macros/i22616b.scala b/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")
+
+    '{()}
diff --git a/tests/run-macros/i22616c.check b/tests/run-macros/i22616c.check
@@ -0,0 +1 @@
+_B_
diff --git a/tests/run-macros/i22616c/Macro_4.scala 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)
diff --git a/tests/run-macros/i22616c/MyTypeRepr_3.scala b/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${expr.show}"))
+  }
+}
diff --git a/tests/run-macros/i22616c/SealedTrait3_2.scala b/tests/run-macros/i22616c/SealedTrait3_2.scala
@@ -0,0 +1,8 @@
+sealed trait SealedTrait3[+A, +B]
+object SealedTrait3 {
+  final case class AB1[+B, +A](a: B, b: A) extends SealedTrait3[B, A]
+  final case class AB2[+C, +D](a: C, b: D) extends SealedTrait3[D, C]
+  final case class A[+T](a: T) extends SealedTrait3[T, Nothing]
+  @caseName("_B_") final case class B[+T](b: T) extends SealedTrait3[Nothing, T]
+  case object Neither extends SealedTrait3[Nothing, Nothing]
+}
diff --git a/tests/run-macros/i22616c/Test_5.scala b/tests/run-macros/i22616c/Test_5.scala
@@ -0,0 +1,2 @@
+@main def Test =
+  println(Macro.myMacro[SealedTrait3.B[Any]]())
diff --git a/tests/run-macros/i22616c/caseName_1.scala b/tests/run-macros/i22616c/caseName_1.scala
@@ -0,0 +1,14 @@
+import scala.quoted.*
+
+final case class caseName(name: String) extends scala.annotation.Annotation
+object caseName {
+  // This demonstrates a workaround for issue #22616.
+  given FromExpr[caseName] =
+    new FromExpr[caseName] {
+      override def unapply(x: Expr[caseName])(using Quotes): Option[caseName] =
+        x match {
+          case '{ new `caseName`(${ Expr(name) }) } => Some(caseName(name))
+          case _                                    => println(x.show); None
+        }
+    }
+}

Original file line number	Diff line number	Diff line change
`@@ -222,7 +222,7 @@ trait QuotesAndSplices {`
`222`	`222`	`if ctx.mode.is(Mode.InPatternAlternative) then`
`223`	`223`	`report.error(IllegalVariableInPatternAlternative(tree.name), tree.srcPos)`
`224`	`224`	`val typeSym = inContext(quotePatternOuterContext(ctx)) {`
`225`		`- newSymbol(ctx.owner, tree.name.toTypeName, Case, typeSymInfo, NoSymbol, tree.span)`
	`225`	`+ newSymbol(ctx.owner, tree.name.toTypeName, Synthetic \| Case, typeSymInfo, NoSymbol, tree.span)`
`226`	`226`	`}`
`227`	`227`	`addQuotedPatternTypeVariable(typeSym)`
`228`	`228`	`Bind(typeSym, untpd.Ident(nme.WILDCARD).withType(typeSymInfo)).withSpan(tree.span)`