MillBuildRootModule: Don't include generated wrapper files in sources (#4851)

The generated files under the `wrapped` directory wrap and duplicate the
original files. Although they're sources to the compiler, they're not
sources for the user and/or editor.

Also, when compiling the wrapped files, we already translate compiler
error messages back to the original files, hence the user/editor should
not need to deal with these intermediate files. Before this change, the
IDE sometimes shows the generated `build.mill` instead of the original
`build.mill` when jumping to definitions or using other code navigation
options. If the user edited these files, changes were lost later.

This PR removes the wrapped files from `generatedSources`, so they no
longer appear in the IDE. Those files are still fed via
`allScalaSourceFiles` to the compiler.

Tested manually with Metals 1.5.2+97-5a09352f-SNAPSHOT/vscode and
IntelliJ 2025.1.

Pull request: #4851

Author: lefou

integration/ide/bsp-server/resources/snapshots/build-targets-sources.json

@@ -75,11 +75,6 @@
           "kind": 2,
           "generated": false
         },
-        {
-          "uri": "file:///workspace/out/mill-build/generatedScriptSources.dest/wrapped",
-          "kind": 2,
-          "generated": true
-        },
         {
           "uri": "file:///workspace/out/mill-build/generatedScriptSources.dest/support",
           "kind": 2,

integration/ide/gen-idea/resources/extended/idea/mill_modules/mill-build.iml

@@ -4,7 +4,6 @@
         <exclude-output/>
         <content url="file://$MODULE_DIR$/../..">
             <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/generatedScriptSources.dest/support" isTestSource="false" generated="true"/>
-            <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/generatedScriptSources.dest/wrapped" isTestSource="false" generated="true"/>
             <sourceFolder url="file://$MODULE_DIR$/../../build.mill" isTestSource="false"/>
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/src" isTestSource="false"/>
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/resources" type="java-resource"/>
@@ -118,4 +117,4 @@
         <orderEntry type="library" scope="RUNTIME" name="xz-1.9.jar" level="project"/>
         <orderEntry type="library" name="zstd-jni-1.5.7-2.jar" level="project"/>
     </component>
-</module>
+</module>

integration/ide/gen-idea/resources/extended/idea/mill_modules/mill-build.mill-build.iml

@@ -5,9 +5,6 @@
         <content url="file://$MODULE_DIR$/../../out/mill-build/mill-build/generatedScriptSources.dest/support">
             <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/mill-build/generatedScriptSources.dest/support" isTestSource="false" generated="true"/>
         </content>
-        <content url="file://$MODULE_DIR$/../../out/mill-build/mill-build/generatedScriptSources.dest/wrapped">
-            <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/mill-build/generatedScriptSources.dest/wrapped" isTestSource="false" generated="true"/>
-        </content>
         <content url="file://$MODULE_DIR$/../../mill-build">
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/build.mill" isTestSource="false"/>
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/mill-build/src" isTestSource="false"/>

integration/ide/gen-idea/resources/hello-idea/idea/mill_modules/mill-build.iml

@@ -4,7 +4,6 @@
         <exclude-output/>
         <content url="file://$MODULE_DIR$/../..">
             <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/generatedScriptSources.dest/support" isTestSource="false" generated="true"/>
-            <sourceFolder url="file://$MODULE_DIR$/../../out/mill-build/generatedScriptSources.dest/wrapped" isTestSource="false" generated="true"/>
             <sourceFolder url="file://$MODULE_DIR$/../../build.mill" isTestSource="false"/>
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/src" isTestSource="false"/>
             <sourceFolder url="file://$MODULE_DIR$/../../mill-build/resources" type="java-resource"/>

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

@@ -96,9 +96,15 @@ trait MillBuildRootModule()(implicit
   override def platformSuffix: T[String] = s"_mill${BuildInfo.millBinPlatform}"
 
   override def generatedSources: T[Seq[PathRef]] = Task {
-    generatedScriptSources()._1 ++ generatedScriptSources()._2
+    generatedScriptSources()._2
   }
 
+  /**
+   * Additional script files, we generate, since not all Mill source
+   * files (e.g. `.sc` and `.mill`) can be fed to the compiler as-is.
+   * The wrapped files aren't supposed to appear under [[generatedSources]] and [[allSources]],
+   * since they are derived from [[sources]] and would confuse any further tooling like IDEs.
+   */
   def generatedScriptSources: T[MillBuildRootModule.GeneratedScriptSourcesResult] = Task {
     val wrapped = Task.dest / "wrapped"
     val support = Task.dest / "support"
@@ -211,15 +217,28 @@ trait MillBuildRootModule()(implicit
     codesig.transitiveCallGraphHashes
   }
 
+  /**
+   * All mill build source files.
+   * These files are the inputs but not necessarily the same files we feed to the compiler,
+   * since we need to process `.mill` files and generate additional Scala files from it.
+   */
   override def sources: T[Seq[PathRef]] = Task {
     scriptSources() ++ super.sources()
   }
 
   override def allSourceFiles: T[Seq[PathRef]] = Task {
+    val allMillSources =
+      // the real input-sources
+      allSources() ++
+        // also sources, but derived from `scriptSources`
+        generatedScriptSources()._1
+
     val candidates =
-      Lib.findSourceFiles(allSources(), Seq("scala", "java") ++ buildFileExtensions.asScala)
+      Lib.findSourceFiles(allMillSources, Seq("scala", "java") ++ buildFileExtensions.asScala.toSeq)
+
     // We need to unlist those files, which we replaced by generating wrapper scripts
     val filesToExclude = Lib.findSourceFiles(scriptSources(), buildFileExtensions.asScala.toSeq)
+
     candidates.filterNot(filesToExclude.contains).map(PathRef(_))
   }