Symbol#source correct for all phases

A combination of the inliner missing opportunities for setting defTrees
with the correct inlined source information and some suspect post
erasure logic in Symbol#source led to the same-source check in
ExpandPrivate failing in joint-compilation scenarios resulting in
multi-file programs being incorrectly rejected for access violations.

Author: milessabin

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -626,15 +626,27 @@ object Symbols {
     final def symbol(implicit ev: DontUseSymbolOnSymbol): Nothing = unsupported("symbol")
     type DontUseSymbolOnSymbol
 
-    final def source(implicit ctx: Context): SourceFile =
-      if (!defTree.isEmpty && !ctx.erasedTypes) defTree.source
-      else this match {
-        case cls: ClassSymbol => cls.sourceOfClass
-        case _ =>
-          if (denot.is(Module)) denot.moduleClass.source
-          else if (denot.exists) denot.owner.source
-          else NoSource
-      }
+    final def source(implicit ctx: Context): SourceFile = {
+      def valid(src: SourceFile): SourceFile =
+        if (src.exists && src.file.extension != "class") src
+        else NoSource
+
+      if (!denot.exists) NoSource
+      else
+        valid(defTree.source) match {
+          case NoSource =>
+            valid(denot.owner.source) match {
+              case NoSource =>
+                this match {
+                  case cls: ClassSymbol      => valid(cls.sourceOfClass)
+                  case _ if denot.is(Module) => valid(denot.moduleClass.source)
+                  case _ => NoSource
+                }
+              case src => src
+            }
+          case src => src
+        }
+    }
 
     /** A symbol related to `sym` that is defined in source code.
      *

compiler/src/dotty/tools/dotc/typer/Inliner.scala

@@ -165,6 +165,7 @@ object Inliner {
           case tree: SeqLiteral => finalize(tree, untpd.SeqLiteral(transform(tree.elems), transform(tree.elemtpt))(curSource))
           case tree: TypeTree => tpd.TypeTree(tree.tpe)(ctx.withSource(curSource)).withSpan(tree.span)
           case tree: Bind => finalize(tree, untpd.Bind(tree.name, transform(tree.body))(curSource))
+          case tree: DefTree => super.transform(tree).setDefTree
           case _ => super.transform(tree)
         })
         assert(transformed.isInstanceOf[EmptyTree[_]] || transformed.isInstanceOf[EmptyValDef[_]] || transformed.source == curSource)

tests/pos/inline-joint/defn.scala

@@ -0,0 +1,5 @@
+object Foo {
+  inline def foo = new { bar(0) }
+
+  def bar(i: => Int): Unit = ()
+}

tests/pos/inline-joint/use.scala

@@ -0,0 +1,3 @@
+object Test {
+  val v = Foo.foo
+}