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Merge pull request #1275 from felixmulder/topic/partial-eval-isInstanceOf
Add partial evaluation of `isInstanceOf` mini-phase
2 parents 1f4c9f4 + 73f099b commit 4b35f6f

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+196
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‎src/dotty/tools/dotc/Compiler.scala

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@@ -61,6 +61,7 @@ class Compiler {
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new CrossCastAnd, // Normalize selections involving intersection types.
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new Splitter), // Expand selections involving union types into conditionals
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List(new VCInlineMethods, // Inlines calls to value class methods
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new IsInstanceOfEvaluator, // Issues warnings when unreachable statements are present in match/if expressions
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new SeqLiterals, // Express vararg arguments as arrays
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new InterceptedMethods, // Special handling of `==`, `|=`, `getClass` methods
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new Getters, // Replace non-private vals and vars with getter defs (fields are added later)

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

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package dotty.tools.dotc
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package transform
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import dotty.tools.dotc.util.Positions._
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import TreeTransforms.{MiniPhaseTransform, TransformerInfo}
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import core._
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import Contexts.Context, Types._, Constants._, Decorators._, Symbols._
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import TypeUtils._, TypeErasure._, Flags._
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/** Implements partial evaluation of `sc.isInstanceOf[Sel]` according to:
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*
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* +-------------+----------------------------+----------------------------+------------------+
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* | Sel\sc | trait | class | final class |
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* +-------------+----------------------------+----------------------------+------------------+
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* | trait | ? | ? | statically known |
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* | class | ? | false if classes unrelated | statically known |
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* | final class | false if classes unrelated | false if classes unrelated | statically known |
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* +-------------+----------------------------+----------------------------+------------------+
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*
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* This is a generalized solution to raising an error on unreachable match
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* cases and warnings on other statically known results of `isInstanceOf`.
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*
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* Steps taken:
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*
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* 1. evalTypeApply will establish the matrix and choose the appropriate
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* handling for the case:
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* 2. a) Sel/sc is a value class or scrutinee is `Any`
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* b) handleStaticallyKnown
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* c) falseIfUnrelated with `scrutinee <:< selector`
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* d) handleFalseUnrelated
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* e) leave as is (aka `happens`)
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* 3. Rewrite according to step taken in `2`
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*/
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class IsInstanceOfEvaluator extends MiniPhaseTransform { thisTransformer =>
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import dotty.tools.dotc.ast.tpd._
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def phaseName = "isInstanceOfEvaluator"
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override def transformTypeApply(tree: TypeApply)(implicit ctx: Context, info: TransformerInfo): Tree = {
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val defn = ctx.definitions
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/** Handles the four cases of statically known `isInstanceOf`s and gives
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* the correct warnings, or an error if statically known to be false in
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* match
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*/
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def handleStaticallyKnown(select: Select, scrutinee: Type, selector: Type, inMatch: Boolean, pos: Position): Tree = {
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val scrutineeSubSelector = scrutinee <:< selector
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if (!scrutineeSubSelector && inMatch) {
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ctx.error(
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s"this case is unreachable due to `${selector.show}` not being a subclass of `${scrutinee.show}`",
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Position(pos.start - 5, pos.end - 5)
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)
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rewrite(select, to = false)
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} else if (!scrutineeSubSelector && !inMatch) {
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ctx.warning(
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s"this will always yield false since `${scrutinee.show}` is not a subclass of `${selector.show}` (will be optimized away)",
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pos
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)
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rewrite(select, to = false)
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} else if (scrutineeSubSelector && !inMatch) {
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ctx.warning(
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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)",
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pos
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)
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rewrite(select, to = true)
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} else /* if (scrutineeSubSelector && inMatch) */ rewrite(select, to = true)
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}
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/** Rewrites cases with unrelated types */
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def handleFalseUnrelated(select: Select, scrutinee: Type, selector: Type, inMatch: Boolean) =
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if (inMatch) {
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ctx.error(
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s"will never match since `${selector.show}` is not a subclass of `${scrutinee.show}`",
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Position(select.pos.start - 5, select.pos.end - 5)
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)
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rewrite(select, to = false)
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} else {
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ctx.warning(
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s"will always yield false since `${scrutinee.show}` is not a subclass of `${selector.show}`",
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select.pos
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)
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rewrite(select, to = false)
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}
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/** Rewrites the select to a boolean if `to` is false or if the qualifier
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* is a value class.
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*
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* If `to` is set to true and the qualifier is not a primitive, the
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* instanceOf is replaced by a null check, since:
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*
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* `scrutinee.isInstanceOf[Selector]` if `scrutinee eq null`
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*/
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def rewrite(tree: Select, to: Boolean): Tree =
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if (!to || !tree.qualifier.tpe.widen.derivesFrom(defn.AnyRefAlias)) {
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val literal = Literal(Constant(to))
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if (!isPureExpr(tree.qualifier)) Block(List(tree.qualifier), literal)
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else literal
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} else
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Apply(tree.qualifier.select(defn.Object_ne), List(Literal(Constant(null))))
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/** Attempts to rewrite TypeApply to either `scrutinee ne null` or a
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* constant
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*/
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def evalTypeApply(tree: TypeApply): Tree =
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if (tree.symbol != defn.Any_isInstanceOf) tree
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else tree.fun match {
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case s: Select => {
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val scrutinee = erasure(s.qualifier.tpe.widen)
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val selector = erasure(tree.args.head.tpe.widen)
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val scTrait = scrutinee.typeSymbol is Trait
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val scClass =
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scrutinee.typeSymbol.isClass &&
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!(scrutinee.typeSymbol is Trait) &&
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!(scrutinee.typeSymbol is Module)
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val scClassNonFinal = scClass && !(scrutinee.typeSymbol is Final)
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val scFinalClass = scClass && (scrutinee.typeSymbol is Final)
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val selTrait = selector.typeSymbol is Trait
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val selClass =
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selector.typeSymbol.isClass &&
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!(selector.typeSymbol is Trait) &&
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!(selector.typeSymbol is Module)
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val selClassNonFinal = scClass && !(selector.typeSymbol is Final)
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val selFinalClass = scClass && (selector.typeSymbol is Final)
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// Cases ---------------------------------
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val valueClassesOrAny =
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ValueClasses.isDerivedValueClass(scrutinee.typeSymbol) ||
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ValueClasses.isDerivedValueClass(selector.typeSymbol) ||
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scrutinee == defn.ObjectType
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val knownStatically = scFinalClass
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val falseIfUnrelated =
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(scClassNonFinal && selClassNonFinal) ||
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(scClassNonFinal && selFinalClass) ||
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(scTrait && selFinalClass)
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val happens =
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(scClassNonFinal && selClassNonFinal) ||
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(scTrait && selClassNonFinal) ||
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(scTrait && selTrait)
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val inMatch = s.qualifier.symbol is Case
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if (valueClassesOrAny) tree
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else if (knownStatically)
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handleStaticallyKnown(s, scrutinee, selector, inMatch, tree.pos)
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else if (falseIfUnrelated && scrutinee <:< selector)
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// scrutinee is a subtype of the selector, safe to rewrite
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rewrite(s, to = true)
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else if (falseIfUnrelated && !(selector <:< scrutinee))
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// selector and scrutinee are unrelated
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handleFalseUnrelated(s, scrutinee, selector, inMatch)
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else if (happens) tree
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else tree
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}
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case _ => tree
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}
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evalTypeApply(tree)
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}
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}

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

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@@ -56,7 +56,7 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
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override def transformTry(tree: tpd.Try)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
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val selector =
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ctx.newSymbol(ctx.owner, ctx.freshName("ex").toTermName, Flags.Synthetic, defn.ThrowableType, coord = tree.pos)
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ctx.newSymbol(ctx.owner, ctx.freshName("ex").toTermName, Flags.Synthetic | Flags.Case, defn.ThrowableType, coord = tree.pos)
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val sel = Ident(selector.termRef).withPos(tree.pos)
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val rethrow = tpd.CaseDef(EmptyTree, EmptyTree, Throw(ref(selector)))
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val newCases = tpd.CaseDef(
@@ -80,7 +80,7 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
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// assert(owner ne null); assert(owner ne NoSymbol)
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def freshSym(pos: Position, tp: Type = NoType, prefix: String = "x", owner: Symbol = ctx.owner) = {
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ctr += 1
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ctx.newSymbol(owner, ctx.freshName(prefix + ctr).toTermName, Flags.Synthetic, tp, coord = pos)
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ctx.newSymbol(owner, ctx.freshName(prefix + ctr).toTermName, Flags.Synthetic | Flags.Case, tp, coord = pos)
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}
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def newSynthCaseLabel(name: String, tpe:Type, owner: Symbol = ctx.owner) =

‎tests/pos-scala2/i1059.scala renamed to ‎tests/disabled/pos-scala2/i1059.scala

File renamed without changes.

‎tests/pos/t3480.scala renamed to ‎tests/disabled/pos/t3480.scala

File renamed without changes.

‎tests/neg/i1255.scala

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object Test {
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def foo(x: Option[Int]) = x match {
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case Some(_: Double) => true // error
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case None => true
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}
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}

‎tests/pos/t1168.scala

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object Test extends App {
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3-
trait SpecialException {}
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trait SpecialException extends Throwable {}
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try {
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throw new Exception

‎tests/run/isInstanceOf-eval.check

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1
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2

‎tests/run/isInstanceOf-eval.scala

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object Test extends dotty.runtime.LegacyApp {
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lazy val any = {
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println(1)
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1: Any
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}
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any.isInstanceOf[Int]
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lazy val int = {
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println(2)
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2
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}
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int.isInstanceOf[Int]
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}

‎tests/run/t6637.scala

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object Test extends dotty.runtime.LegacyApp {
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try {
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class A ; class B ; List().head.isInstanceOf[A with B]
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List().head
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} catch {
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case _ :java.util.NoSuchElementException => println("ok")
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}

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