Merge pull request #991 from joroKr21/lazy-type-params

Fix Lazy implicit resolution with type parameters
milessabin · Mar 24, 2020 · 17e3c6f · 17e3c6f
2 parents 88a803f + 65243a0
commit 17e3c6f
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Showing 2 changed files with 34 additions and 6 deletions.
diff --git a/core/src/main/scala/shapeless/lazy.scala b/core/src/main/scala/shapeless/lazy.scala
@@ -295,17 +295,21 @@ class LazyMacros(val c: whitebox.Context) extends CaseClassMacros with OpenImpli
 
       private var current = Option.empty[State]
 
+      private def typeParamsToWildcards(tpe: Type): Type = tpe.map { t =>
+        val sym = t.typeSymbol
+        if (sym.isParameter) boundedWildcardType(sym.info.asInstanceOf[TypeBounds]) else t
+      }
+
       def resolveInstance(state: State)(tpe: Type): Option[(State, Tree)] = {
         val former = State.current
         State.current = Some(state)
         val (state0, tree) =
           try {
-            val tree = c.inferImplicitValue(tpe, silent = true)
-            if(tree.isEmpty) {
-              tpe.typeSymbol.annotations.
-                find(_.tree.tpe =:= typeOf[_root_.scala.annotation.implicitNotFound]).foreach { _ =>
-                  setAnnotation(implicitNotFoundMessage(c)(tpe))
-                }
+            val tree = c.inferImplicitValue(tpe, silent = true) orElse c.inferImplicitValue(typeParamsToWildcards(tpe), silent = true)
+            if (tree.isEmpty) {
+              tpe.typeSymbol.annotations
+                .find(_.tree.tpe =:= typeOf[_root_.scala.annotation.implicitNotFound])
+                .foreach(_ => setAnnotation(implicitNotFoundMessage(c)(tpe)))
             }
             (State.current.get, tree)
           } finally {

diff --git a/core/src/test/scala/shapeless/lazy.scala b/core/src/test/scala/shapeless/lazy.scala
@@ -334,3 +334,27 @@ class LazyStrictTests {
     implicitly[Strict[Readable[Id]]]
   }
 }
+
+object TestLazyWithTypeParametersAndBounds {
+  trait Foo
+  case class BarFoo(i: Int) extends Foo
+
+  trait Fooer[Tpe, FooTpe] {
+    def makeFoo(obj: Tpe): FooTpe
+  }
+
+  object Fooer {
+    implicit val barFooer: Fooer[Int, BarFoo] = null
+  }
+
+  class Finder[Tpe] {
+    def find[F <: Foo](implicit fooer: Fooer[Tpe, F]) = fooer
+    def findLazy[F <: Foo](implicit fooer: Lazy[Fooer[Tpe, F]]) = fooer
+    def findNoBounds[F](implicit fooer: Lazy[Fooer[Tpe, F]]) = fooer
+  }
+
+  val intFinder = new Finder[Int]
+  intFinder.find
+  intFinder.findLazy
+  intFinder.findNoBounds
+}