Make "goto-definition" more useful.

When invoking "goto-definition" on a definition node itself, we now return all
overriding or overridden definitions, in all sources. Previously, we returned
only overriding definitions in the same source. But it's arguably more useful
to know about overriding definitions in other sources because these are harder
to find manually. Performance, is not an issue because it's only invoked if one
is already on a definition, which should be relatively rare.

Author: odersky

language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala

@@ -211,11 +211,10 @@ class DottyLanguageServer extends LanguageServer
       /*isIncomplete = */ false, items.map(completionItem).asJava))
   }
 
-  /** If cursor is on a reference, show its definition and all overriding definitions.
+  /** If cursor is on a reference, show its definition and all overriding definitions in
+   *  the same source as the primary definition.
    *  If cursor is on a definition, show this definition together with all overridden
-   *  and overriding definitions.
-   *  For performance reasons we currently look for overrides only in the file
-   *  where `sym` is defined.
+   *  and overriding definitions (in all sources).
    */
   override def definition(params: TextDocumentPositionParams) = computeAsync { cancelToken =>
     val uri = new URI(params.getTextDocument.getUri)
@@ -228,9 +227,13 @@ class DottyLanguageServer extends LanguageServer
 
     if (sym == NoSymbol) Nil.asJava
     else {
-      val trees = SourceTree.fromSymbol(sym.topLevelClass.asClass).toList
-      var include = Include.overriding
-      if (enclTree.isInstanceOf[MemberDef]) include |= Include.overridden
+      val (trees, include) =
+        if (enclTree.isInstanceOf[MemberDef])
+          (driver.allTreesContaining(sym.name.sourceModuleName.toString),
+           Include.overriding | Include.overridden)
+        else
+          (SourceTree.fromSymbol(sym.topLevelClass.asClass).toList,
+           Include.overriding)
       val defs = Interactive.namedTrees(trees, include, sym)
       defs.map(d => location(d.namePos)).asJava
     }