Introduce miniphase that normalizes names of type definitions in packages for error reporting

Author: biboudis

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

@@ -113,6 +113,7 @@ class Compiler {
     List(new Flatten,                // Lift all inner classes to package scope
          new RestoreScopes,          // Repair scopes rendered invalid by moving definitions in prior phases of the group
          new RenameLifted,           // Renames lifted classes to local numbering scheme
+         new NormalizePackageDefs,   // Normalizes names of type definitions in packages to avoid OS-dependent name clashes/shadowing
          new TransformWildcards,     // Replace wildcards with default values
          new MoveStatics,            // Move static methods to companion classes
          new ExpandPrivate,          // Widen private definitions accessed from nested classes

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

@@ -0,0 +1,23 @@
+package dotty.tools.dotc.transform
+
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Decorators._
+import dotty.tools.dotc.transform.MegaPhase.MiniPhase
+
+/** Normalizes names of type definitions to avoid OS-dependent name clashes/shadowing */
+
+class NormalizePackageDefs extends MiniPhase {
+  import tpd._
+
+  override def phaseName = "normalizePackageDefs"
+
+  override def transformPackageDef(tree: PackageDef)(implicit ctx: Context) : Tree = {
+
+    val typeList = tree.stats.filter(s => s.denot.isType)
+    val normalizedDefinitionList = typeList.map(s => s.denot.toString.toLowerCase())
+    if (normalizedDefinitionList.distinct.size < typeList.size) ctx.error(i"package ${tree.denot.name} contains definitions with duplicate names, in a case-insensitive manner", tree.pos)
+
+    tree
+  }
+}

tests/neg/i2673.scala

@@ -0,0 +1,4 @@
+package Foos //error
+
+class Foo
+class foo