Remove RHS of definitions in inline traits

Author: timotheeandres

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

@@ -91,7 +91,8 @@ 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
+    List(new PruneInlineTraits,
+         new PruneErasedDefs,        // Drop erased definitions from scopes and simplify erased expressions
          new UninitializedDefs,      // Replaces `compiletime.uninitialized` by `_`
          new InlinePatterns,         // Remove placeholders of inlined patterns
          new VCInlineMethods,        // Inlines calls to value class methods

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

@@ -0,0 +1,48 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import Contexts._
+import DenotTransformers.SymTransformer
+import Flags._
+import SymDenotations._
+import Symbols._
+import MegaPhase.MiniPhase
+import ast.tpd
+
+class PruneInlineTraits extends MiniPhase with SymTransformer { thisTransform =>
+  import tpd._
+  import PruneInlineTraits._
+
+  override def phaseName: String = PruneInlineTraits.name
+
+  override def description: String = PruneInlineTraits.description
+
+  override def transformSym(sym: SymDenotation)(using Context): SymDenotation =
+    if isEraseable(sym) then sym.copySymDenotation(initFlags = sym.flags | Deferred)
+    else sym
+
+  override def transformValDef(tree: ValDef)(using Context): ValDef =
+    if isEraseable(tree.symbol) then cpy.ValDef(tree)(rhs = EmptyTree)
+    else tree
+
+  override def transformDefDef(tree: DefDef)(using Context): DefDef =
+    if isEraseable(tree.symbol) then cpy.DefDef(tree)(rhs = EmptyTree)
+    else tree
+
+  private def isEraseable(sym: SymDenotation)(using Context): Boolean =
+    sym.owner.isInlineTrait
+    && !sym.isConstructor
+    && !sym.is(Param)
+    && !sym.is(ParamAccessor)
+    && !sym.is(Private)
+    && !sym.isLocalDummy
+    && !sym.isType
+}
+
+object PruneInlineTraits {
+  import tpd._
+
+  val name: String = "pruneInlineTraits"
+  val description: String = "drop rhs definitions in inline traits"
+}