Avoid name clashes when generating synthetic companion objects.

Author: odersky

src/dotty/tools/dotc/core/NameOps.scala

@@ -72,6 +72,7 @@ object NameOps {
     def isSetterName = name endsWith SETTER_SUFFIX
     def isSingletonName = name endsWith SINGLETON_SUFFIX
     def isModuleClassName = name endsWith MODULE_SUFFIX
+    def isAvoidClashName = name endsWith AVOID_CLASH_SUFFIX
     def isImportName = name startsWith IMPORT
     def isFieldName = name endsWith LOCAL_SUFFIX
     def isInheritedName = name.length > 0 && name.head == '(' && name.startsWith(nme.INHERITED)
@@ -129,11 +130,19 @@ object NameOps {
     /** If name ends in module class suffix, drop it */
     def stripModuleClassSuffix: Name =
       if (isModuleClassName) name dropRight MODULE_SUFFIX.length else name
+      
+    /** Append a suffix so that this name does not clash with another name in the same scope */
+    def avoidClashName: TermName = (name ++ AVOID_CLASH_SUFFIX).toTermName
+
+    /** If name ends in "avoid clash" suffix, drop it */
+    def stripAvoidClashSuffix: Name =
+      if (isAvoidClashName) name dropRight AVOID_CLASH_SUFFIX.length else name
 
     /** If flags is a ModuleClass but not a Package, add module class suffix */
-    def adjustIfModuleClass(flags: Flags.FlagSet): N =
-      if (flags is (ModuleClass, butNot = Package)) name.asTypeName.moduleClassName.asInstanceOf[N]
-      else name
+    def adjustIfModuleClass(flags: Flags.FlagSet): N = {
+      if (flags is (ModuleClass, butNot = Package)) name.asTypeName.moduleClassName
+      else stripAvoidClashSuffix
+    }.asInstanceOf[N]
 
     /** The superaccessor for method with given name */
     def superName: TermName =  (nme.SUPER_PREFIX ++ name).toTermName

src/dotty/tools/dotc/core/StdNames.scala

@@ -107,6 +107,7 @@ object StdNames {
     val INTERPRETER_WRAPPER_SUFFIX: N = "$object"
     val LOCALDUMMY_PREFIX: N          = "<local "       // owner of local blocks
     val MODULE_SUFFIX: N              = NameTransformer.MODULE_SUFFIX_STRING
+    val AVOID_CLASH_SUFFIX: N         = "$_avoid_name_clash_$"
     val MODULE_VAR_SUFFIX: N          = "$module"
     val NAME_JOIN: N                  = NameTransformer.NAME_JOIN_STRING
     val USCORE_PARAM_PREFIX: N        = "_$"

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -171,9 +171,14 @@ object SymDenotations {
       myInfo = tp
     }
 
-    /** The name, except if this is a module class, strip the module class suffix */
+    /** The name, except 
+     *   - if this is a module class, strip the module class suffix 
+     *   - if this is a companion object with a clash-avoiding name, strip the 
+     *     "avoid clash" suffix
+     */
     def effectiveName(implicit ctx: Context) =
-      if (this is ModuleClass) name.stripModuleClassSuffix else name
+      if (this is ModuleClass) name.stripModuleClassSuffix 
+      else name.stripAvoidClashSuffix
 
     /** The privateWithin boundary, NoSymbol if no boundary is given.
      */

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

@@ -81,7 +81,15 @@ class FirstTransform extends MiniPhaseTransform with IdentityDenotTransformer wi
 
     def addMissingCompanions(stats: List[Tree]): List[Tree] = stats map {
       case stat: TypeDef if singleClassDefs contains stat.name =>
-        Thicket(stat :: newCompanion(stat.name.toTermName).trees)
+        val objName = stat.name.toTermName
+        val nameClash = stats.exists {
+          case other: MemberDef => 
+            other.name == objName && other.symbol.info.isParameterless
+          case _ =>
+            false
+        }
+        val uniqueName = if (nameClash) objName.avoidClashName else objName
+        Thicket(stat :: newCompanion(uniqueName).trees)
       case stat => stat
     }
 

tests/pending/pos/S5.scala renamed to tests/new/S5.scala

@@ -1,4 +1,5 @@
-/* Here's a fragment of a Scala encoding for the Keris module system;
+/* Original comment:
+ * Here's a fragment of a Scala encoding for the Keris module system;
 ** the compiler claims:
 **
 ** S5.scala:28: value n in class N of type N.this._N.n