Merge pull request #9514 from dotty-staging/add-asExprOf

Add quoted.Expr.asExprOf and Reflection.Tree.{asExprOf, isExpr}

Author: nicolasstucki

compiler/src/dotty/tools/dotc/tastyreflect/ReflectionCompilerInterface.scala

@@ -272,8 +272,10 @@ class ReflectionCompilerInterface(val rootContext: core.Contexts.Context) extend
     override def unapply(x: Any): Option[Term] = x match
       case _ if Unapply_TypeTest.unapply(x).isDefined => None
       case _: tpd.PatternTree @unchecked => None
-      case x: tpd.SeqLiteral @unchecked => Some(x)
       case x: tpd.Tree @unchecked if x.isTerm => Some(x)
+      case x: tpd.SeqLiteral @unchecked => Some(x)
+      case x: tpd.Inlined @unchecked => Some(x)
+      case x: tpd.NamedArg @unchecked => Some(x)
       case _ => None
   }
 

library/src-bootstrapped/scala/quoted/Expr.scala

@@ -41,11 +41,14 @@ abstract class Expr[+T] private[scala] {
     !scala.internal.quoted.Expr.unapply[EmptyTuple, EmptyTuple](this)(using that, false, qctx).isEmpty
 
   /** Checked cast to a `quoted.Expr[U]` */
-  def cast[U](using tp: scala.quoted.Type[U])(using qctx: QuoteContext): scala.quoted.Expr[U] = {
+  def cast[U](using tp: scala.quoted.Type[U])(using qctx: QuoteContext): scala.quoted.Expr[U] = asExprOf[U]
+
+  /** Convert this to an `quoted.Expr[X]` if this expression is a valid expression of type `X` or throws */
+  def asExprOf[X](using tp: scala.quoted.Type[X])(using qctx: QuoteContext): scala.quoted.Expr[X] = {
     val tree = this.unseal
     val expectedType = tp.unseal.tpe
     if (tree.tpe <:< expectedType)
-      this.asInstanceOf[scala.quoted.Expr[U]]
+      this.asInstanceOf[scala.quoted.Expr[X]]
     else
       throw new scala.tasty.reflect.ExprCastError(
         s"""Expr: ${tree.show}
@@ -178,7 +181,7 @@ object Expr {
   /** Given a tuple of the form `(Expr[A1], ..., Expr[An])`, outputs a tuple `Expr[(A1, ..., An)]`. */
   def ofTuple[T <: Tuple: Tuple.IsMappedBy[Expr]: Type](tup: T)(using qctx: QuoteContext): Expr[Tuple.InverseMap[T, Expr]] = {
     val elems: Seq[Expr[Any]] = tup.asInstanceOf[Product].productIterator.toSeq.asInstanceOf[Seq[Expr[Any]]]
-    ofTupleFromSeq(elems).cast[Tuple.InverseMap[T, Expr]]
+    ofTupleFromSeq(elems).asExprOf[Tuple.InverseMap[T, Expr]]
   }
 
   /** Find an implicit of type `T` in the current scope given by `qctx`.

library/src-bootstrapped/scala/quoted/util/ExprMap.scala

@@ -102,22 +102,18 @@ trait ExprMap {
       }
 
       def transformTerm(tree: Term, tpe: Type)(using ctx: Context): Term =
-        tree match {
-        case _: Closure =>
-          tree
-        case _: Inlined =>
-          transformTermChildren(tree, tpe)
-        case _ =>
-          tree.tpe.widen match {
-            case _: MethodType | _: PolyType =>
-              transformTermChildren(tree, tpe)
-            case _ =>
-              type X
-              val expr = tree.seal.asInstanceOf[Expr[X]]
-              val t = tpe.seal.asInstanceOf[quoted.Type[X]]
-              transform(expr)(using qctx, t).unseal
-          }
-      }
+        tree match
+          case _: Closure =>
+            tree
+          case _: Inlined =>
+            transformTermChildren(tree, tpe)
+          case _ if tree.isExpr =>
+            type X
+            val expr = tree.seal.asInstanceOf[Expr[X]]
+            val t = tpe.seal.asInstanceOf[quoted.Type[X]]
+            transform(expr)(using qctx, t).unseal
+          case _ =>
+            transformTermChildren(tree, tpe)
 
       def transformTypeTree(tree: TypeTree)(using ctx: Context): TypeTree = tree
 
@@ -155,7 +151,7 @@ trait ExprMap {
         trees mapConserve (transformTypeCaseDef(_))
 
     }
-    new MapChildren().transformTermChildren(e.unseal, tpe.unseal.tpe).seal.cast[T] // Cast will only fail if this implementation has a bug
+    new MapChildren().transformTermChildren(e.unseal, tpe.unseal.tpe).asExprOf[T]
   }
 
 }

library/src-non-bootstrapped/scala/quoted/Expr.scala

@@ -2,3 +2,4 @@ package scala.quoted
 
 abstract class Expr[+T] private[scala]:
   def unseal(using qctx: QuoteContext): qctx.tasty.Term
+  def asExprOf[X](using tp: scala.quoted.Type[X])(using qctx: QuoteContext): scala.quoted.Expr[X] = ???

library/src/scala/tasty/Reflection.scala

@@ -488,7 +488,28 @@ class Reflection(private[scala] val internal: CompilerInterface) { self =>
       /** Shows the tree as fully typed source code */
       def showWith(syntaxHighlight: SyntaxHighlight)(using ctx: Context): String =
         new SourceCodePrinter[self.type](self)(syntaxHighlight).showTree(tree)
+
+      /** Does this tree represent a valid expression? */
+      def isExpr(using ctx: Context): Boolean =
+        tree match
+          case tree: Term =>
+            tree.tpe.widen match
+              case _: MethodType | _: PolyType => false
+              case _ => true
+          case _ => false
+
     end extension
+
+
+    /** Convert this tree to an `quoted.Expr[T]` if the tree is a valid expression or throws */
+    extension [T](tree: Tree)
+      def asExprOf(using scala.quoted.Type[T])(using QuoteContext): scala.quoted.Expr[T] =
+        if tree.isExpr then
+          new scala.internal.quoted.Expr(tree, internal.compilerId).asExprOf[T]
+        else tree match
+          case tree: Term => throw new Exception("Expected an expression. This is a partially applied Term. Try eta-expanding the term first.")
+          case _ => throw new Exception("Expected a Term but was: " + tree)
+
   end Tree
 
   given (using ctx: Context) as TypeTest[Tree, PackageClause] = internal.PackageClause_TypeTest
@@ -655,15 +676,13 @@ class Reflection(private[scala] val internal: CompilerInterface) { self =>
 
       /** Convert `Term` to an `quoted.Expr[Any]` if the term is a valid expression or throws */
       def seal(using ctx: Context): scala.quoted.Expr[Any] =
-        sealOpt.getOrElse {
-          throw new Exception("Cannot seal a partially applied Term. Try eta-expanding the term first.")
-        }
+        if self.isExpr then new scala.internal.quoted.Expr(self, internal.compilerId)
+        else throw new Exception("Cannot seal a partially applied Term. Try eta-expanding the term first.")
 
       /** Convert `Term` to an `quoted.Expr[Any]` if the term is a valid expression */
       def sealOpt(using ctx: Context): Option[scala.quoted.Expr[Any]] =
-        self.tpe.widen match
-          case _: MethodType | _: PolyType => None
-          case _ => Some(new scala.internal.quoted.Expr(self, internal.compilerId))
+        if self.isExpr then Some(new scala.internal.quoted.Expr(self, internal.compilerId))
+        else None
 
       /** Type of this term */
       def tpe(using ctx: Context): Type = internal.Term_tpe(self)