Suspend macros when class not found during macro expansion

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

@@ -47,6 +47,8 @@ object Splicer {
         interpretedExpr.fold(tree)(macroClosure => PickledQuotes.quotedExprToTree(macroClosure(QuoteContext())))
       }
       catch {
+        case ex: CompilationUnit.SuspendException =>
+          throw ex
         case ex: StopInterpretation =>
           ctx.error(ex.msg, ex.pos)
           EmptyTree
@@ -348,19 +350,26 @@ object Splicer {
           sw.write("\n")
           throw new StopInterpretation(sw.toString, pos)
         case ex: InvocationTargetException =>
-          val sw = new StringWriter()
-          sw.write("Exception occurred while executing macro expansion.\n")
-          val targetException = ex.getTargetException
-          if (!ctx.settings.Ydebug.value) {
-            val end = targetException.getStackTrace.lastIndexWhere { x =>
-              x.getClassName == method.getDeclaringClass.getCanonicalName && x.getMethodName == method.getName
-            }
-            val shortStackTrace = targetException.getStackTrace.take(end + 1)
-            targetException.setStackTrace(shortStackTrace)
+          ex.getTargetException match {
+            case targetException: NoClassDefFoundError => // FIXME check that the class is beeining compiled now
+              val className = targetException.getMessage
+              if (ctx.settings.XprintSuspension.value)
+                ctx.echo(i"suspension triggered by NoClassDefFoundError($className)", pos) // TODO improve message
+              ctx.compilationUnit.suspend() // this throws a SuspendException
+            case targetException =>
+              val sw = new StringWriter()
+              sw.write("Exception occurred while executing macro expansion.\n")
+              if (!ctx.settings.Ydebug.value) {
+                val end = targetException.getStackTrace.lastIndexWhere { x =>
+                  x.getClassName == method.getDeclaringClass.getCanonicalName && x.getMethodName == method.getName
+                }
+                val shortStackTrace = targetException.getStackTrace.take(end + 1)
+                targetException.setStackTrace(shortStackTrace)
+              }
+              targetException.printStackTrace(new PrintWriter(sw))
+              sw.write("\n")
+              throw new StopInterpretation(sw.toString, pos)
           }
-          targetException.printStackTrace(new PrintWriter(sw))
-          sw.write("\n")
-          throw new StopInterpretation(sw.toString, pos)
       }
 
     /** List of classes of the parameters of the signature of `sym` */

compiler/src/dotty/tools/dotc/typer/Inliner.scala

@@ -1242,9 +1242,9 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(implicit ctx: Context) {
     if dependencies.nonEmpty then
       for sym <- dependencies do
         if ctx.compilationUnit.source.file == sym.associatedFile then
-          ctx.error(em"Cannot call macro $sym defined in the same source file", body.sourcePos)
+          ctx.error(em"Cannot call macro $sym defined in the same source file", call.sourcePos)
         if (ctx.settings.XprintSuspension.value)
-          ctx.echo(i"suspension triggered by macro call to ${sym.showLocated} in ${sym.associatedFile}", body.sourcePos)
+          ctx.echo(i"suspension triggered by macro call to ${sym.showLocated} in ${sym.associatedFile}", call.sourcePos)
       ctx.compilationUnit.suspend() // this throws a SuspendException
 
     val evaluatedSplice = Splicer.splice(body, inlinedFrom.sourcePos, MacroClassLoader.fromContext)(ctx1)

tests/neg-macros/macros-in-same-project-4.check

@@ -1,8 +1,6 @@
--- Error: tests/neg-macros/macros-in-same-project-4/Bar.scala:5:13 -----------------------------------------------------
-5 |  Foo.myMacro() // error
-  |  ^^^^^^^^^^^^^
-  |Failed to expand macro. This macro depends on an implementation that is defined in the same project and not yet compiled.
-  |In particular method myMacro depends on method aMacroImplementation.
-  |
-  |Moving method aMacroImplementation to a different project would fix this.
-  | This location is in code that was inlined at Bar.scala:5
+Cyclic macro dependencies in tests/neg-macros/macros-in-same-project-4/Bar.scala.
+Compilation stopped since no further progress can be made.
+
+To fix this, place macros in one set of files and their callers in another.
+
+Compiling with  -Xprint-suspension   gives more information.

tests/neg-macros/macros-in-same-project-4/Bar.scala

@@ -1,8 +1,9 @@
+// nopos-error
 import scala.quoted._
 
 object Bar {
 
-  Foo.myMacro() // error
+  Foo.myMacro()
 
   def hello()(given QuoteContext): Expr[Unit] = '{ println("Hello") }
 }

tests/neg-macros/macros-in-same-project-5/Bar.scala

@@ -0,0 +1,10 @@
+import scala.quoted._
+
+object Bar {
+
+  Foo.myMacro() // error
+
+  def aMacroImplementation(given QuoteContext): Expr[Unit] = Bar.hello()
+
+  def hello()(given QuoteContext): Expr[Unit] = '{ println("Hello") }
+}

tests/neg-macros/macros-in-same-project-5/Foo.scala

@@ -0,0 +1,8 @@
+import scala.quoted._
+import Bar.aMacroImplementation
+
+object Foo {
+
+  inline def myMacro(): Unit = ${ aMacroImplementation }
+
+}