[2.0.x] fix: Fix build.sbt file loading in subdirs (#9165) (#9168)

**Problem**
Projects defined in subdirectory build.sbt files are
not correctly resolved to the base directory relative to the file.

**Solution**
Call resolveBase.

buildfile/src/main/scala/sbt/internal/EvaluateConfigurations.scala

@@ -172,8 +172,7 @@ private[sbt] object EvaluateConfigurations {
         val compositeProjects = definitions
           .values(loader)
           .collect { case p: CompositeProject => p }
-        // todo: resolveBase?
-        CompositeProject.expand(compositeProjects) // .map(resolveBase(file.getParentFile, _))
+        CompositeProject.expand(compositeProjects)
       }
       val loadedDslEntries = dslEntries.map(_.result.apply(loader))
       val settings = loadedDslEntries.collect { case DslEntry.ProjectSettings(s) => s }.flatten

buildfile/src/main/scala/sbt/internal/LoadedSbtFile.scala

@@ -16,15 +16,15 @@ import java.nio.file.Path
  * Represents the exported contents of a .sbt file.  Currently, that includes the list of settings,
  * the values of Project vals, and the import statements for all defined vals/defs.
  */
-private[sbt] final class LoadedSbtFile(
-    val settings: Seq[Setting[?]],
-    val projects: Seq[Project],
-    val importedDefs: Seq[String],
-    val manipulations: Seq[Project => Project],
+private[sbt] final case class LoadedSbtFile(
+    settings: Seq[Setting[?]],
+    projects: Seq[Project],
+    importedDefs: Seq[String],
+    manipulations: Seq[Project => Project],
     // TODO - we may want to expose a simpler interface on top of here for the set command,
     // rather than what we have now...
-    val definitions: DefinedSbtValues,
-    val generatedFiles: Seq[Path]
+    definitions: DefinedSbtValues,
+    generatedFiles: Seq[Path]
 ) {
   // We still use merge for now.  We track originating sbt file in an alternative manner.
   def merge(o: LoadedSbtFile): LoadedSbtFile =

main/src/main/scala/sbt/internal/Load.scala

@@ -30,7 +30,7 @@ import sbt.io.{ GlobFilter, IO }
 import sbt.librarymanagement.{ Configuration, Configurations, IvyPaths, Resolver, ScalaArtifacts }
 import sbt.nio.Settings
 import sbt.util.{ Logger, Show }
-import xsbti.{ FileConverter, HashedVirtualFileRef, VirtualFile }
+import xsbti.{ FileConverter, HashedVirtualFileRef, PathBasedFile, VirtualFile }
 import xsbti.compile.{ ClasspathOptionsUtil, Compilers }
 import java.io.File
 import java.net.URI
@@ -1327,13 +1327,19 @@ private[sbt] object Load {
     // TODO - We should import vals defined in other sbt files here, if we wish to
     // share.  For now, build.sbt files have their own unique namespace.
     def loadSettingsFile(src: VirtualFile): LoadedSbtFile =
-      EvaluateConfigurations.evaluateSbtFile(
+      val evaluated = EvaluateConfigurations.evaluateSbtFile(
         eval(),
         src,
         IO.readStream(src.input()).linesIterator.toList,
         loadedPlugins.detected.imports,
         0
       )(loader)
+      evaluated.copy(
+        projects = evaluated.projects.map: p =>
+          src match
+            case file: PathBasedFile => resolveBase(file.toPath.toFile.getParentFile)(p)
+            case _                   => p
+      )
     // How to merge SbtFiles we read into one thing
     def merge(ls: Seq[LoadedSbtFile]): LoadedSbtFile = ls.foldLeft(LoadedSbtFile.empty) {
       _.merge(_)

sbt-app/src/sbt-test/project-load/subdirectory/build.sbt

@@ -0,0 +1,10 @@
+lazy val foo = project
+
+@transient
+lazy val check = taskKey[Unit]("")
+
+scalaVersion := "3.8.3"
+LocalRootProject / check := {
+  assert((foo / Compile / scalacOptions).value == List("-Xmacro-settings:a:a"),
+    s"${(foo / Compile / scalacOptions).value}")
+}

sbt-app/src/sbt-test/project-load/subdirectory/changes/Good.scala

@@ -0,0 +1,3 @@
+package example
+
+class A

sbt-app/src/sbt-test/project-load/subdirectory/foo/A.scala

@@ -0,0 +1,3 @@
+package example
+
+class A("

sbt-app/src/sbt-test/project-load/subdirectory/foo/build.sbt

@@ -0,0 +1,4 @@
+lazy val foo = rootProject
+  .settings(
+    Compile / scalacOptions += "-Xmacro-settings:a:a"
+  )

sbt-app/src/sbt-test/project-load/subdirectory/test

@@ -0,0 +1,6 @@
+> check
+
+# check that it fails to compile a bad source
+-> compile
+$ copy-file changes/Good.scala foo/A.scala
+> compile