Fix callTrace of inlined methods (#18738)

We need to keep the reference to the called method, not only the symbol
of the to level class. This is important for the traces of the `assert`
method that is defined in a different file. This might also be useful
for macro annotations.

This is also a solution to the awkward Select vs. Ident distinction to
identify macros in `YCheckPositions`.

Author: odersky

.github/workflows/ci.yaml

@@ -209,6 +209,10 @@ jobs:
         run: sbt ";dist/pack ;scala3-bootstrapped/compile ;scala3-bootstrapped/test"
         shell: cmd
 
+      - name: Test with Scala 2 library TASTy
+        run: sbt ";set ThisBuild/Build.useScala2LibraryTasty := true ;scala3-bootstrapped/testCompilation i5" # only test a subset of test to avoid doubling the CI execution time
+        shell: cmd
+
       - name: Scala.js Test
         run: sbt ";sjsJUnitTests/test ;set sjsJUnitTests/scalaJSLinkerConfig ~= switchToESModules ;sjsJUnitTests/test ;sjsCompilerTests/test"
         shell: cmd

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -661,7 +661,8 @@ object Trees {
    *
    *  @param  call      Info about the original call that was inlined
    *                    Until PostTyper, this is the full call, afterwards only
-   *                    a reference to the toplevel class from which the call was inlined.
+   *                    a reference to the method or the top-level class from
+   *                    which the call was inlined.
    *  @param  bindings  Bindings for proxies to be used in the inlined code
    *  @param  expansion The inlined tree, minus bindings.
    *

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -299,20 +299,6 @@ object Inlines:
     (new Reposition).transform(tree)
   end reposition
 
-  /** Leave only a call trace consisting of
-   *  - a reference to the top-level class from which the call was inlined,
-   *  - the call's position
-   *  in the call field of an Inlined node.
-   *  The trace has enough info to completely reconstruct positions.
-   *  Note: For macros it returns a Select and for other inline methods it returns an Ident (this distinction is only temporary to be able to run YCheckPositions)
-   */
-  def inlineCallTrace(callSym: Symbol, pos: SourcePosition)(using Context): Tree = {
-    assert(ctx.source == pos.source)
-    val topLevelCls = callSym.topLevelClass
-    if (callSym.is(Macro)) ref(topLevelCls.owner).select(topLevelCls.name)(using ctx.withOwner(topLevelCls.owner)).withSpan(pos.span)
-    else Ident(topLevelCls.typeRef).withSpan(pos.span)
-  }
-
   private object Intrinsics:
     import dotty.tools.dotc.reporting.Diagnostic.Error
     private enum ErrorKind:

compiler/src/dotty/tools/dotc/transform/PickleQuotes.scala

@@ -304,7 +304,7 @@ object PickleQuotes {
     def pickleAsTasty() = {
       val body1 =
         if body.isType then body
-        else Inlined(Inlines.inlineCallTrace(ctx.owner, quote.sourcePos), Nil, body)
+        else Inlined(ref(ctx.owner.topLevelClass.typeRef).withSpan(quote.span), Nil, body)
       val pickleQuote = PickledQuotes.pickleQuote(body1)
       val pickledQuoteStrings = pickleQuote match
         case x :: Nil => Literal(Constant(x))

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -367,7 +367,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
           val pos = call.sourcePos
           CrossVersionChecks.checkExperimentalRef(call.symbol, pos)
           withMode(Mode.InlinedCall)(transform(call))
-          val callTrace = Inlines.inlineCallTrace(call.symbol, pos)(using ctx.withSource(pos.source))
+          val callTrace = ref(call.symbol)(using ctx.withSource(pos.source)).withSpan(pos.span)
           cpy.Inlined(tree)(callTrace, transformSub(bindings), transform(expansion)(using inlineContext(tree)))
         case templ: Template =>
           withNoCheckNews(templ.parents.flatMap(newPart)) {

compiler/src/dotty/tools/dotc/transform/YCheckPositions.scala

@@ -35,7 +35,7 @@ class YCheckPositions extends Phase {
                 val currentSource = sources.head
                 assert(tree.source == currentSource, i"wrong source set for $tree # ${tree.uniqueId} of ${tree.getClass}, set to ${tree.source} but context had $currentSource\n ${tree.symbol.flagsString}")
 
-            // Recursivlely check children while keeping track of current source
+            // Recursively check children while keeping track of current source
             reporting.trace(i"check pos ${tree.getClass} ${tree.source} ${sources.head} $tree") {
               tree match {
                 case tree @ Inlined(_, bindings, expansion) if tree.inlinedFromOuterScope =>
@@ -46,7 +46,7 @@ class YCheckPositions extends Phase {
                   sources = old
                 case tree @ Inlined(call, bindings, expansion) =>
                   // bindings.foreach(traverse(_)) // TODO check inline proxies (see tests/tun/lst)
-                  sources = call.symbol.topLevelClass.source :: sources
+                  sources = call.symbol.source :: sources
                   if (!isMacro(call)) // FIXME macro implementations can drop Inlined nodes. We should reinsert them after macro expansion based on the positions of the trees
                     traverse(expansion)(using inlineContext(tree).withSource(sources.head))
                   sources = sources.tail
@@ -61,10 +61,10 @@ class YCheckPositions extends Phase {
 
   private def isMacro(call: Tree)(using Context) =
     call.symbol.is(Macro) ||
-    (call.symbol.isClass && call.tpe.derivesFrom(defn.MacroAnnotationClass)) ||
-    // The call of a macro after typer is encoded as a Select while other inlines are Ident
-    // TODO remove this distinction once Inline nodes of expanded macros can be trusted (also in Inliner.inlineCallTrace)
-    (!(ctx.phase <= postTyperPhase) && call.isInstanceOf[Select])
+        (call.symbol.isClass && call.tpe.derivesFrom(defn.MacroAnnotationClass)) ||
+    // In 3.0-3.3, the call of a macro after typer is encoded as a Select while other inlines are Ident.
+    // In those versions we kept the reference to the top-level class instead of the methods.
+    (!(ctx.phase <= postTyperPhase) && call.symbol.isClass && call.isInstanceOf[Select])
 
 }