diff options
| -rw-r--r-- | src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala | 29 |
1 files changed, 19 insertions, 10 deletions
diff --git a/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala b/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala index 03ebb9515..8b1baa11a 100644 --- a/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala +++ b/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala @@ -8,8 +8,15 @@ import Contexts.Context, Types._, Constants._, Decorators._, Symbols._ import TypeUtils._, TypeErasure._ -/** Implements partial `isInstanceOf` evaluation according to the matrix on: - * https://github.com/lampepfl/dotty/issues/1255 +/** Implements partial evaluation of `sc.isInstanceOf[Sel]` according to: + * + * +-------------+----------------------------+----------------------------+------------------+ + * | Sel\sc | trait | class | final class | + * +-------------+----------------------------+----------------------------+------------------+ + * | trait | ? | ? | statically known | + * | class | ? | false if classes unrelated | statically known | + * | final class | false if classes unrelated | false if classes unrelated | statically known | + * +-------------+----------------------------+----------------------------+------------------+ * * This is a generalized solution to raising an error on unreachable match * cases and warnings on other statically known results of `isInstanceOf`. @@ -36,26 +43,28 @@ class IsInstanceOfEvaluator extends MiniPhaseTransform { thisTransformer => * the correct warnings, or an error if statically known to be false in * match */ - def handleStaticallyKnown(tree: Select, scrutinee: Type, selector: Type, inMatch: Boolean, pos: Position): Tree = - if (!(scrutinee <:< selector) && inMatch) { + def handleStaticallyKnown(tree: Select, scrutinee: Type, selector: Type, inMatch: Boolean, pos: Position): Tree = { + val scrutineeSubSelector = scrutinee <:< selector + if (!scrutineeSubSelector && inMatch) { ctx.error( s"this case is unreachable due to `${selector.show}` not being a subclass of `${scrutinee.show}`", Position(pos.start - 5, pos.end - 5) ) rewrite(tree, to = false) - } else if (!(scrutinee <:< selector) && !inMatch) { + } else if (!scrutineeSubSelector && !inMatch) { ctx.warning( s"this will always yield false since `${scrutinee.show}` is not a subclass of `${selector.show}` (will be optimized away)", pos ) rewrite(tree, to = false) - } else if (scrutinee <:< selector && !inMatch) { + } else if (scrutineeSubSelector && !inMatch) { ctx.warning( - s"this will always yield true since `${scrutinee.show}` is a subclass of `${selector.show}` (will be optimized away)", + s"this will always yield true if the scrutinee is non-null, since `${scrutinee.show}` is a subclass of `${selector.show}` (will be optimized away)", pos ) rewrite(tree, to = true) - } else /* if (scrutinee <:< selector && inMatch) */ rewrite(tree, to = true) + } else /* if (scrutineeSubSelector && inMatch) */ rewrite(tree, to = true) + } /** Rewrites cases with unrelated types */ def handleFalseUnrelated(tree: Select, scrutinee: Type, selector: Type, inMatch: Boolean) = @@ -74,12 +83,12 @@ class IsInstanceOfEvaluator extends MiniPhaseTransform { thisTransformer => } /** Rewrites the select to a boolean if `to` is false or if the qualifier - * is a primitive. + * is a value class. * * If `to` is set to true and the qualifier is not a primitive, the * instanceOf is replaced by a null check, since: * - * `srutinee.isInstanceOf[Selector]` if `scrutinee eq null` + * `scrutinee.isInstanceOf[Selector]` if `scrutinee eq null` */ def rewrite(tree: Select, to: Boolean): Tree = if (!to || !tree.qualifier.tpe.widen.derivesFrom(defn.AnyRefAlias)) |