Provide a context ClassLoader to macros

compiler/src/dotty/tools/dotc/transform/Splicer.scala

@@ -44,13 +44,19 @@ object Splicer {
       val macroOwner = newSymbol(ctx.owner, nme.MACROkw, Macro | Synthetic, defn.AnyType, coord = tree.span)
       try
         inContext(ctx.withOwner(macroOwner)) {
-          val interpreter = new Interpreter(pos, classLoader)
-
-          // Some parts of the macro are evaluated during the unpickling performed in quotedExprToTree
-          val interpretedExpr = interpreter.interpret[scala.quoted.QuoteContext => scala.quoted.Expr[Any]](tree)
-          val interpretedTree = interpretedExpr.fold(tree)(macroClosure => PickledQuotes.quotedExprToTree(macroClosure(QuoteContext())))
-
-          checkEscapedVariables(interpretedTree, macroOwner)
+          val oldContextClassLoader = Thread.currentThread().getContextClassLoader
+          Thread.currentThread().setContextClassLoader(classLoader)
+          try {
+            val interpreter = new Interpreter(pos, classLoader)
+
+            // Some parts of the macro are evaluated during the unpickling performed in quotedExprToTree
+            val interpretedExpr = interpreter.interpret[scala.quoted.QuoteContext => scala.quoted.Expr[Any]](tree)
+            val interpretedTree = interpretedExpr.fold(tree)(macroClosure => PickledQuotes.quotedExprToTree(macroClosure(QuoteContext())))
+
+            checkEscapedVariables(interpretedTree, macroOwner)
+          } finally {
+            Thread.currentThread().setContextClassLoader(oldContextClassLoader)
+          }
         }.changeOwner(macroOwner, ctx.owner)
       catch {
         case ex: CompilationUnit.SuspendException =>

tests/pos-macros/macro-classloaders/Caller.scala

@@ -0,0 +1,3 @@
+object Caller {
+  Macro.f
+}

tests/pos-macros/macro-classloaders/Macro.scala

@@ -0,0 +1,15 @@
+import java.net.URLClassLoader
+
+import scala.quoted._
+
+object Macro { self =>
+  inline def f: Any = ${ impl }
+
+  def impl(using QuoteContext): Expr[Any] = {
+    //println("======== "+self.getClass.getClassLoader.asInstanceOf[URLClassLoader].getURLs.mkString("; "))
+    //println("  ====== "+Thread.currentThread().getContextClassLoader.asInstanceOf[URLClassLoader].getURLs.mkString("; "))
+    assert(getClass.getClassLoader eq Thread.currentThread().getContextClassLoader,
+      "Macro ClassLoader should be available as context ClassLoader")
+    '{""}
+  }
+}