.

runner/src/mill/runner/MillBuildRootModule.scala

@@ -38,6 +38,23 @@ class MillBuildRootModule()(implicit
 
   override def millSourcePath = millBuildRootModuleInfo.projectRoot / os.up / "mill-build"
 
+  override def resolveDeps(
+      deps: Task[Agg[BoundDep]],
+      sources: Boolean = false
+  ): Task[Agg[PathRef]] =
+    T.task {
+      if (sources == true) super.resolveDeps(deps, true)()
+      else {
+        // We need to resolve the sources to make GenIdeaExtendedTests pass,
+        // because those do not call `resolveDeps` explicitly for build file
+        // `import $ivy`s but instead rely on the deps that are resolved as
+        // part of the bootstrapping process. We thus need to make sure
+        // bootstrapping the rootModule ends up putting the sources on disk
+        val unused = super.resolveDeps(deps, true)()
+        super.resolveDeps(deps, false)()
+      }
+    }
+
   override def scalaVersion = "2.13.10"
 
   def scriptSources = T.sources {