diff options
-rw-r--r-- | src/compiler/scala/tools/nsc/typechecker/Infer.scala | 15 | ||||
-rw-r--r-- | test/files/neg/t5845.check | 5 | ||||
-rw-r--r-- | test/files/pos/t4881.scala | 31 |
3 files changed, 45 insertions, 6 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala index 291b7f1827..22e78a1e36 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala @@ -508,7 +508,7 @@ trait Infer { val tvars = tparams map freshVar if (isConservativelyCompatible(restpe.instantiateTypeParams(tparams, tvars), pt)) map2(tparams, tvars)((tparam, tvar) => - instantiateToBound(tvar, varianceInTypes(formals)(tparam))) + instantiateToBound(tvar, inferVariance(formals, restpe)(tparam))) else tvars map (tvar => WildcardType) } @@ -638,13 +638,24 @@ trait Infer { "argument expression's type is not compatible with formal parameter type" + foundReqMsg(tp1, pt1)) } } + val targs = solvedTypes( - tvars, tparams, tparams map varianceInTypes(formals), + tvars, tparams, tparams map inferVariance(formals, restpe), false, lubDepth(formals) max lubDepth(argtpes) ) adjustTypeArgs(tparams, tvars, targs, restpe) } + /** Determine which variance to assume for the type paraneter. We first chose the variance + * that minimizes any formal parameters. If that is still undetermined, because the type parameter + * does not appear as a formal parameter type, then we pick the variance so that it minimizes the + * method's result type instead. + */ + private def inferVariance(formals: List[Type], restpe: Type)(tparam: Symbol): Int = { + val v = varianceInTypes(formals)(tparam) + if (v != VarianceFlags) v else varianceInType(restpe)(tparam) + } + private[typechecker] def followApply(tp: Type): Type = tp match { case NullaryMethodType(restp) => val restp1 = followApply(restp) diff --git a/test/files/neg/t5845.check b/test/files/neg/t5845.check index 8c6100d6de..c0b402fccb 100644 --- a/test/files/neg/t5845.check +++ b/test/files/neg/t5845.check @@ -1,7 +1,4 @@ -t5845.scala:9: error: value +++ is not a member of Int - println(5 +++ 5) - ^ t5845.scala:15: error: value +++ is not a member of Int println(5 +++ 5) ^ -two errors found +one error found diff --git a/test/files/pos/t4881.scala b/test/files/pos/t4881.scala new file mode 100644 index 0000000000..46cfad9793 --- /dev/null +++ b/test/files/pos/t4881.scala @@ -0,0 +1,31 @@ +class Contra[-T] +trait A +trait B extends A +trait C extends B + +// test improved variance inference: first try formals to see in which variance positions the type param appears; +// only when that fails to determine variance, look at result type +object Test { + def contraLBUB[a >: C <: A](): Contra[a] = null + def contraLB[a >: C](): Contra[a] = null + +{ + val x = contraLBUB() //inferred Contra[C] instead of Contra[A] + val x1: Contra[A] = x +} + +{ + val x = contraLB() //inferred Contra[C] instead of Contra[Any] + val x1: Contra[Any] = x +} + +{ + val x = contraLBUB // make sure it does the same thing as its ()-less counterpart + val x1: Contra[A] = x +} + +{ + val x = contraLB + val x1: Contra[Any] = x +} +} |