Merge pull request #3905 from gourlaysama/wip/t5691-2

SI-5691 lint warning when a type parameter shadows an existing type.

3 files changed, 26 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/settings/Warnings.scala b/src/compiler/scala/tools/nsc/settings/Warnings.scala
index bec068b56a..4c37633301 100644
--- a/src/compiler/scala/tools/nsc/settings/Warnings.scala
+++ b/src/compiler/scala/tools/nsc/settings/Warnings.scala
@@ -38,6 +38,7 @@ trait Warnings {
     warnMissingInterpolator,
     warnDocDetached,
     warnPrivateShadow,
+    warnTypeParameterShadow,
     warnPolyImplicitOverload,
     warnOptionImplicit,
     warnDelayedInit,
@@ -83,6 +84,8 @@ trait Warnings {
                                 "A ScalaDoc comment appears to be detached from its element.")
   val warnPrivateShadow        = lintflag("private-shadow",
                                 "A private field (or class parameter) shadows a superclass field.")
+  val warnTypeParameterShadow  = lintflag("type-parameter-shadow",
+                                "A local type parameter shadows a type already in scope.")
   val warnPolyImplicitOverload = lintflag("poly-implicit-overload",
                                 "Parameterized overloaded implicit methods are not visible as view bounds")
   val warnOptionImplicit       = lintflag("option-implicit",
diff --git a/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala b/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
index 89b064e7c1..8d29d28908 100644
--- a/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala
@@ -600,6 +600,23 @@ trait TypeDiagnostics {
         )
     }
 
+    // warn about class/method/type-members' type parameters that shadow types already in scope
+    def warnTypeParameterShadow(tparams: List[TypeDef], sym: Symbol): Unit =
+      if (settings.warnTypeParameterShadow && !isPastTyper && !sym.isSynthetic) {
+        def enclClassOrMethodOrTypeMember(c: Context): Context =
+          if (!c.owner.exists || c.owner.isClass || c.owner.isMethod || (c.owner.isType && !c.owner.isParameter)) c
+          else enclClassOrMethodOrTypeMember(c.outer)
+
+        val tt = tparams.filter(_.name != typeNames.WILDCARD).foreach { tp =>
+        // we don't care about type params shadowing other type params in the same declaration
+        enclClassOrMethodOrTypeMember(context).outer.lookupSymbol(tp.name, s => s != tp.symbol && s.hasRawInfo && reallyExists(s)) match {
+          case LookupSucceeded(_, sym2) => context.warning(tp.pos,
+            s"type parameter ${tp.name} defined in $sym shadows $sym2 defined in ${sym2.owner}. You may want to rename your type parameter, or possibly remove it.")
+          case _ =>
+        }
+      }
+    }
+
     /** Report a type error.
      *
      *  @param pos    The position where to report the error
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 0621fbefe4..422b940cd3 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1726,6 +1726,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
              |you want, you must write the annotation class in Java.""".stripMargin)
       }
 
+      warnTypeParameterShadow(tparams1, clazz)
+
       if (!isPastTyper) {
         for (ann <- clazz.getAnnotation(DeprecatedAttr)) {
           val m = companionSymbolOf(clazz, context)
@@ -2128,6 +2130,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
       val tparams1 = ddef.tparams mapConserve typedTypeDef
       val vparamss1 = ddef.vparamss mapConserve (_ mapConserve typedValDef)
 
+      warnTypeParameterShadow(tparams1, meth)
+
       meth.annotations.map(_.completeInfo())
 
       for (vparams1 <- vparamss1; vparam1 <- vparams1 dropRight 1)
@@ -2204,6 +2208,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
       val typedMods = typedModifiers(tdef.mods)
       tdef.symbol.annotations.map(_.completeInfo())
 
+      warnTypeParameterShadow(tparams1, tdef.symbol)
+
       // @specialized should not be pickled when compiling with -no-specialize
       if (settings.nospecialization && currentRun.compiles(tdef.symbol)) {
         tdef.symbol.removeAnnotation(definitions.SpecializedClass)