Cleanup after simple/script modules (#5953)

Follow ups to #5951 to clean up
things that were messy in the original PR

- `def discover` forwarder was unnecessary
- Break up `FileImportGraph.parseBuildFiles` and split out and inline
the parts we need in `MillBuildRootModule`

Author: lihaoyi

core/api/src/mill/api/internal/RootModule0.scala

@@ -30,7 +30,6 @@ abstract class RootModule0(
   // `Discover` needs to be defined by every concrete `BaseModule` object, to gather
   // compile-time metadata about the tasks and commands at for use at runtime
   protected def millDiscover: Discover
-  def discover: Discover = millDiscover
 
   // We need to propagate the `Discover` object implicitly throughout the module tree
   // so it can be used for override detection

core/resolve/src/mill/resolve/Resolve.scala

@@ -211,7 +211,7 @@ private[mill] object Resolve {
         p,
         r.segments.last.value,
         p match {
-          case e: ExternalModule => e.discover
+          case e: ExternalModule => e.moduleCtx.discover
           case _ => rootModule.moduleCtx.discover
         },
         args,

runner/daemon/src/mill/daemon/MillBuildBootstrap.scala

@@ -4,7 +4,6 @@ import mill.api.daemon.internal.{
   BuildFileApi,
   CompileProblemReporter,
   EvaluatorApi,
-  MillScalaParser,
   PathRefApi,
   RootModuleApi
 }
@@ -15,8 +14,9 @@ import mill.api.daemon.Watchable
 import mill.api.internal.RootModule
 import mill.api.{BuildCtx, PathRef, SelectMode}
 import mill.internal.PrefixLogger
-import mill.meta.{FileImportGraph, MillBuildRootModule}
+import mill.meta.MillBuildRootModule
 import mill.meta.CliImports
+import mill.meta.FileImportGraph.findRootBuildFiles
 import mill.server.Server
 import mill.util.BuildInfo
 
@@ -122,12 +122,13 @@ class MillBuildBootstrap(
             res
           }
         } else {
-          val parsedScriptFiles = FileImportGraph
-            .parseBuildFiles(
-              projectRoot,
-              currentRoot / os.up,
-              output,
-              MillScalaParser.current.value
+          val (useDummy, foundRootBuildFileName) = findRootBuildFiles(projectRoot)
+
+          val headerData =
+            if (!os.exists(projectRoot / foundRootBuildFileName)) ""
+            else mill.constants.Util.readBuildHeader(
+              (projectRoot / foundRootBuildFileName).toNIO,
+              foundRootBuildFileName
             )
 
           val state =
@@ -143,10 +144,10 @@ class MillBuildBootstrap(
                     upickle.read[Map[
                       String,
                       ujson.Value
-                    ]](mill.internal.Util.parsedHeaderData(parsedScriptFiles.headerData))
+                    ]](mill.internal.Util.parsedHeaderData(headerData))
                   )
                 )
-              RunnerState(Some(bootstrapModule), Nil, None, Some(parsedScriptFiles.buildFile))
+              RunnerState(Some(bootstrapModule), Nil, None, Some(foundRootBuildFileName))
             }
 
           state

runner/meta/src/mill/meta/FileImportGraph.scala

@@ -17,12 +17,7 @@ import mill.internal.Util.backtickWrap
  * @param metaBuild If `true`, a meta-build is enabled
  */
 @internal
-case class FileImportGraph(
-    seenScripts: Map[os.Path, String],
-    errors: Seq[String],
-    buildFile: String,
-    headerData: String
-)
+case class FileImportGraph(seenScripts: Map[os.Path, String], errors: Seq[String])
 
 /**
  * Logic around traversing the `import $file` graph, extracting necessary info
@@ -43,7 +38,8 @@ object FileImportGraph {
       topLevelProjectRoot: os.Path,
       projectRoot: os.Path,
       output: os.Path,
-      parser: MillScalaParser = MillScalaParser.current.value
+      parser: MillScalaParser,
+      walked: Seq[os.Path]
   ): FileImportGraph = {
     val seenScripts = mutable.Map.empty[os.Path, String]
     val errors = mutable.Buffer.empty[String]
@@ -97,22 +93,9 @@ object FileImportGraph {
 
     processScript(projectRoot / foundRootBuildFileName, useDummy)
 
-    val walked = walkBuildFiles(projectRoot, output)
     walked.foreach(processScript(_))
 
-    val headerData =
-      if (!os.exists(projectRoot / foundRootBuildFileName)) ""
-      else mill.constants.Util.readBuildHeader(
-        (projectRoot / foundRootBuildFileName).toNIO,
-        foundRootBuildFileName
-      )
-
-    new FileImportGraph(
-      seenScripts.toMap,
-      errors.toSeq,
-      foundRootBuildFileName,
-      headerData
-    )
+    new FileImportGraph(seenScripts.toMap, errors.toSeq)
   }
 
   def findRootBuildFiles(projectRoot: os.Path) = {

runner/meta/src/mill/meta/MillBuildRootModule.scala

@@ -44,21 +44,24 @@ trait MillBuildRootModule()(using
   val scriptSourcesPaths = BuildCtx.withFilesystemCheckerDisabled {
     FileImportGraph
       .walkBuildFiles(rootModuleInfo.projectRoot / os.up, rootModuleInfo.output)
-      .sorted
+      .sorted // Ensure ordering is deterministic
   }
 
   /**
    * All script files (that will get wrapped later)
    * @see [[generatedSources]]
    */
-  def scriptSources: T[Seq[PathRef]] = Task.Sources(
-    scriptSourcesPaths* // Ensure ordering is deterministic
-  )
+  def scriptSources: T[Seq[PathRef]] = Task.Sources(scriptSourcesPaths*)
 
   def parseBuildFiles: T[FileImportGraph] = Task {
-    scriptSources()
     BuildCtx.withFilesystemCheckerDisabled {
-      MillBuildRootModule.parseBuildFiles(MillScalaParser.current.value, rootModuleInfo)
+      FileImportGraph.parseBuildFiles(
+        rootModuleInfo.topLevelProjectRoot,
+        rootModuleInfo.projectRoot / os.up,
+        rootModuleInfo.output,
+        MillScalaParser.current.value,
+        scriptSources().map(_.path)
+      )
     }
   }
 
@@ -369,16 +372,4 @@ object MillBuildRootModule {
       output: os.Path,
       topLevelProjectRoot: os.Path
   )
-
-  def parseBuildFiles(
-      parser: MillScalaParser,
-      millBuildRootModuleInfo: RootModule.Info
-  ): FileImportGraph = {
-    FileImportGraph.parseBuildFiles(
-      millBuildRootModuleInfo.topLevelProjectRoot,
-      millBuildRootModuleInfo.projectRoot / os.up,
-      millBuildRootModuleInfo.output,
-      parser
-    )
-  }
 }