Refactorings and fixes to erased definition handling (#23404)

These are cleanups and bug-fixes. They don't change the semantics of
erasedDefinitions

Author: odersky

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -92,8 +92,7 @@ class Compiler {
          new ExplicitSelf,           // Make references to non-trivial self types explicit as casts
          new StringInterpolatorOpt,  // Optimizes raw and s and f string interpolators by rewriting them to string concatenations or formats
          new DropBreaks) ::          // Optimize local Break throws by rewriting them
-    List(new PruneErasedDefs,        // Drop erased definitions from scopes and simplify erased expressions
-         new UninitializedDefs,      // Replaces `compiletime.uninitialized` by `_`
+    List(new UninitializedDefs,      // Replaces `compiletime.uninitialized` by `_`
          new InlinePatterns,         // Remove placeholders of inlined patterns
          new VCInlineMethods,        // Inlines calls to value class methods
          new SeqLiterals,            // Express vararg arguments as arrays

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

@@ -588,14 +588,18 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
     case New(_) | Closure(_, _, _) =>
       Pure
     case TypeApply(fn, _) =>
-      if (fn.symbol.is(Erased) || fn.symbol == defn.QuotedTypeModule_of || fn.symbol == defn.Predef_classOf) Pure else exprPurity(fn)
+      if tree.tpe.isInstanceOf[MethodOrPoly] then exprPurity(fn)
+      else if fn.symbol == defn.QuotedTypeModule_of || fn.symbol == defn.Predef_classOf then Pure
+      else if fn.symbol == defn.Compiletime_erasedValue && tree.tpe.dealias.isInstanceOf[ConstantType] then Pure
+      else Impure
     case Apply(fn, args) =>
-      if isPureApply(tree, fn) then
-        minOf(exprPurity(fn), args.map(exprPurity)) `min` Pure
-      else if fn.symbol.is(Erased) then
-        Pure
+      val factorPurity = minOf(exprPurity(fn), args.map(exprPurity))
+      if tree.tpe.isInstanceOf[MethodOrPoly] then // no evaluation
+        factorPurity `min` Pure
+      else if isPureApply(tree, fn) then
+        factorPurity `min` Pure
       else if fn.symbol.isStableMember /* && fn.symbol.is(Lazy) */ then
-        minOf(exprPurity(fn), args.map(exprPurity)) `min` Idempotent
+        factorPurity `min` Idempotent
       else
         Impure
     case Typed(expr, _) =>

compiler/src/dotty/tools/dotc/cc/ccConfig.scala

@@ -56,6 +56,6 @@ object ccConfig:
 
   /** Not used currently. Handy for trying out new features */
   def newScheme(using ctx: Context): Boolean =
-    ctx.settings.XdropComments.value
+    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
 
 end ccConfig

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

@@ -107,11 +107,15 @@ class ElimErasedValueType extends MiniPhase with InfoTransformer { thisPhase =>
         (sym1.owner.derivesFrom(defn.PolyFunctionClass) ||
          sym2.owner.derivesFrom(defn.PolyFunctionClass))
 
+      def oneErasedInline =
+        sym1.isInlineMethod && !sym1.isRetainedInlineMethod
+        || sym2.isInlineMethod && !sym2.isRetainedInlineMethod
+
       // super-accessors start as private, and their expanded name can clash after
       // erasure. TODO: Verify that this is OK.
       def bothSuperAccessors = sym1.name.is(SuperAccessorName) && sym2.name.is(SuperAccessorName)
-      if (sym1.name != sym2.name && !bothSuperAccessors ||
-          !info1.matchesLoosely(info2) && !bothPolyApply)
+      if (sym1.name != sym2.name && !bothSuperAccessors
+         || !info1.matchesLoosely(info2) && !bothPolyApply && !oneErasedInline)
         report.error(DoubleDefinition(sym1, sym2, root), root.srcPos)
     }
     while (opc.hasNext) {

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

@@ -20,6 +20,8 @@ import StdNames.*
 import config.Feature
 import inlines.Inlines.inInlineMethod
 import util.Property
+import inlines.Inlines
+import reporting.InlinedAnonClassWarning
 
 object FirstTransform {
   val name: String = "firstTransform"
@@ -207,6 +209,11 @@ class FirstTransform extends MiniPhase with SymTransformer { thisPhase =>
       case _ => tree
     }
 
+  override def transformTypeDef(tree: TypeDef)(using Context): Tree =
+    if tree.symbol.isAnonymousClass && Inlines.inInlineMethod then
+      report.warning(InlinedAnonClassWarning(), tree.symbol.sourcePos)
+    tree
+
   /** Perform one of the following simplification if applicable:
    *
    *      true  && y   ==>  y

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

@@ -2,13 +2,12 @@ package dotty.tools
 package dotc
 package transform
 
-import dotty.tools.dotc.core.Contexts.*
-import dotty.tools.dotc.core.Decorators.*
-import dotty.tools.dotc.core.Symbols.*
-import dotty.tools.dotc.core.Flags.*
-import dotty.tools.dotc.core.Types.*
-import dotty.tools.dotc.transform.MegaPhase.MiniPhase
-import dotty.tools.dotc.inlines.Inlines
+import core.*
+import Contexts.*, Decorators.*, Symbols.*, Flags.*, Types.*
+import MegaPhase.MiniPhase
+import inlines.Inlines
+import ast.tpd
+
 
 /** Check that `tree.rhs` can be right hand-side of an `inline` value definition. */
 class InlineVals extends MiniPhase:
@@ -38,7 +37,10 @@ class InlineVals extends MiniPhase:
       tpt.tpe.widenTermRefExpr.dealiasKeepOpaques.normalized match
         case tp: ConstantType =>
           if !isPureExpr(rhs) then
-            def details = if enclosingInlineds.isEmpty then "" else i"but was: $rhs"
+            def details =
+              if enclosingInlineds.nonEmpty || rhs.isInstanceOf[tpd.Inlined]
+              then i" but was: $rhs"
+              else ""
             report.error(em"inline value must be pure$details", rhs.srcPos)
         case tp =>
           if tp.typeSymbol.is(Opaque) then

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

@@ -335,15 +335,6 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
         }
     }
 
-    private object dropInlines extends TreeMap {
-      override def transform(tree: Tree)(using Context): Tree = tree match {
-        case tree @ Inlined(call, _, expansion) =>
-          val newExpansion = PruneErasedDefs.trivialErasedTree(tree)
-          cpy.Inlined(tree)(call, Nil, newExpansion)
-        case _ => super.transform(tree)
-      }
-    }
-
     def checkUsableAsValue(tree: Tree)(using Context): Tree =
       def unusable(msg: Symbol => Message) =
         errorTree(tree, msg(tree.symbol))
@@ -414,26 +405,13 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
             checkUsableAsValue(tree) match
               case tree1: Select => transformSelect(tree1, Nil)
               case tree1 => tree1
-        case tree: Apply =>
-          val methType = tree.fun.tpe.widen.asInstanceOf[MethodType]
-          val app =
-            if (methType.hasErasedParams)
-              tpd.cpy.Apply(tree)(
-                tree.fun,
-                tree.args.zip(methType.erasedParams).map((arg, isErased) =>
-                  if !isErased then arg
-                  else
-                    if methType.isResultDependent then
-                      Checking.checkRealizable(arg.tpe, arg.srcPos, "erased argument")
-                    if (methType.isImplicitMethod && arg.span.isSynthetic)
-                      arg match
-                        case _: RefTree | _: Apply | _: TypeApply if arg.symbol.is(Erased) =>
-                          dropInlines.transform(arg)
-                        case _ =>
-                          PruneErasedDefs.trivialErasedTree(arg)
-                    else dropInlines.transform(arg)))
-            else
-              tree
+        case app: Apply =>
+          val methType = app.fun.tpe.widen.asInstanceOf[MethodType]
+          if (methType.hasErasedParams)
+            for (arg, isErased) <- app.args.lazyZip(methType.erasedParams) do
+              if isErased then
+                if methType.isResultDependent then
+                  Checking.checkRealizable(arg.tpe, arg.srcPos, "erased argument")
           def app1 =
             // reverse order of transforming args and fun. This way, we get a chance to see other
             // well-formedness errors before reporting errors in possible inferred type args of fun.
@@ -499,7 +477,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
           registerIfHasMacroAnnotations(tree)
           checkErasedDef(tree)
           Checking.checkPolyFunctionType(tree.tpt)
-          val tree1 = cpy.ValDef(tree)(tpt = makeOverrideTypeDeclared(tree.symbol, tree.tpt), rhs = normalizeErasedRhs(tree.rhs, tree.symbol))
+          val tree1 = cpy.ValDef(tree)(tpt = makeOverrideTypeDeclared(tree.symbol, tree.tpt))
           if tree1.removeAttachment(desugar.UntupledParam).isDefined then
             checkStableSelection(tree.rhs)
           processValOrDefDef(super.transform(tree1))
@@ -508,7 +486,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
           checkErasedDef(tree)
           Checking.checkPolyFunctionType(tree.tpt)
           annotateContextResults(tree)
-          val tree1 = cpy.DefDef(tree)(tpt = makeOverrideTypeDeclared(tree.symbol, tree.tpt), rhs = normalizeErasedRhs(tree.rhs, tree.symbol))
+          val tree1 = cpy.DefDef(tree)(tpt = makeOverrideTypeDeclared(tree.symbol, tree.tpt))
           processValOrDefDef(superAcc.wrapDefDef(tree1)(super.transform(tree1).asInstanceOf[DefDef]))
         case tree: TypeDef =>
           registerIfHasMacroAnnotations(tree)
@@ -632,12 +610,6 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
       Checking.checkAndAdaptExperimentalImports(trees)
       super.transformStats(trees, exprOwner, wrapResult)
 
-    /** Transforms the rhs tree into a its default tree if it is in an `erased` val/def.
-     *  Performed to shrink the tree that is known to be erased later.
-     */
-    private def normalizeErasedRhs(rhs: Tree, sym: Symbol)(using Context) =
-      if (sym.isEffectivelyErased) dropInlines.transform(rhs) else rhs
-
     private def registerNeedsInlining(tree: Tree)(using Context): Unit =
       if tree.symbol.is(Inline) && !Inlines.inInlineMethod && !ctx.mode.is(Mode.NoInline) then
         ctx.compilationUnit.needsInlining = true

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

@@ -37,8 +37,7 @@ class ResolveSuper extends MiniPhase with IdentityDenotTransformer { thisPhase =
 
   override def description: String = ResolveSuper.description
 
-  override def runsAfter: Set[String] = Set(ElimByName.name, // verified empirically, need to figure out what the reason is.
-                               PruneErasedDefs.name) // Erased decls make `isCurrent` work incorrectly
+  override def runsAfter: Set[String] = Set(ElimByName.name) // verified empirically, need to figure out what the reason is.
 
   override def changesMembers: Boolean = true // the phase adds super accessors
 

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

@@ -63,7 +63,7 @@ class CompileProgressSpecification {
         "staging",
         "splicing",
         "pickleQuotes",
-        "MegaPhase{pruneErasedDefs,...,arrayConstructors}",
+        "MegaPhase{uninitialized,...,arrayConstructors}",
         "erasure",
         "constructors",
         "genBCode"