Detect cyclic dependencies when loading modules

Fixes scala#12788

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

@@ -350,12 +350,18 @@ object Splicer {
 
     private def interpretedStaticMethodCall(moduleClass: Symbol, fn: Symbol)(implicit env: Env): List[Object] => Object = {
       val (inst, clazz) =
-        if (moduleClass.name.startsWith(str.REPL_SESSION_LINE))
-          (null, loadReplLineClass(moduleClass))
-        else {
-          val inst = loadModule(moduleClass)
-          (inst, inst.getClass)
-        }
+        try
+          if (moduleClass.name.startsWith(str.REPL_SESSION_LINE))
+            (null, loadReplLineClass(moduleClass))
+          else {
+            val inst = loadModule(moduleClass)
+            (inst, inst.getClass)
+          }
+        catch
+          case MissingClassDefinedInCurrentRun(sym)  if ctx.compilationUnit.isSuspendable =>
+            if (ctx.settings.XprintSuspension.value)
+              report.echo(i"suspension triggered by a dependency on $sym", pos)
+            ctx.compilationUnit.suspend() // this throws a SuspendException
 
       val name = fn.name.asTermName
       val method = getMethod(clazz, name, paramsSig(fn))

tests/neg-macros/i12788/Macro.scala

@@ -0,0 +1,21 @@
+import scala.quoted.*
+
+class InlinedInt[T <: Int]
+
+object DFType:
+  trait Width[T]:
+    type Out <: Int
+  transparent inline given [T]: Width[T] = ${ getWidthMacro[T] }
+  def getWidthMacro[T](using Quotes, Type[T]): Expr[Width[T]] =
+    '{
+      new Width[T] {
+        type Out = 1
+      }
+    }
+
+  trait DFBits[W <: Int]
+  object DFBits extends DFBitsCompanion
+
+trait DFToken[T]
+extension [T](token: DFToken[T])(using w: DFType.Width[T])
+  def width: InlinedInt[w.Out] = ???

tests/neg-macros/i12788/Test.scala

@@ -0,0 +1,4 @@
+// nopos-error
+trait DFBitsCompanion:
+  type Token[W <: Int] = DFToken[DFType.DFBits[W]]
+  extension [LW <: Int](lhs: DFType.DFBits.Token[LW]) def foo: Unit = lhs.width