8000 SI-9630 Fix spurious warning related to same-named case accessors · scala/scala@79a52e6 · GitHub
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SI-9630 Fix spurious warning related to same-named case accessors
Hash consing of trees within pattern match analysis was broken, and considered `x1.foo#1` to be the same tree as `x1.foo#2`, even though the two `foo`-s referred to different symbols. The hash consing was based on `Tree#correspondsStructure`, but the predicate in that function cannot veto correspondance, it can only supplement the default structural comparison. I've instead created a custom tree comparison method for use in the pattern matcher that handles the tree shapes that we use.
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‎src/compiler/scala/tools/nsc/transform/patmat/Logic.scala

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@@ -691,7 +691,7 @@ trait ScalaLogic extends Interface with Logic with TreeAndTypeAnalysis {
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// if X is mutable.
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freshExistentialSubtype(t.tpe)
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}
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else trees find (a => a.correspondsStructure(t)(sameValue)) match {
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else trees find (a => equivalentTree(a, t)) match {
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case Some(orig) =>
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debug.patmat("unique tp for tree: " + ((orig, orig.tpe)))
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orig.tpe

‎src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala

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@@ -84,11 +84,15 @@ trait TreeAndTypeAnalysis extends Debugging {
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tp <:< tpImpliedNormalizedToAny
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}
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// TODO: improve, e.g., for constants
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def sameValue(a: Tree, b: Tree): Boolean = (a eq b) || ((a, b) match {
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case (_ : Ident, _ : Ident) => a.symbol eq b.symbol
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case _ => false
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})
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def equivalentTree(a: Tree, b: Tree): Boolean = (a, b) match {
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case (Select(qual1, _), Select(qual2, _)) => equivalentTree(qual1, qual2) && a.symbol == b.symbol
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case (Ident(_), Ident(_)) => a.symbol == b.symbol
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case (Literal(c1), Literal(c2)) => c1 == c2
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case (This(_), This(_)) => a.symbol == b.symbol
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case (Apply(fun1, args1), Apply(fun2, args2)) => equivalentTree(fun1, fun2) && args1.corresponds(args2)(equivalentTree)
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// Those are the only cases we need to handle in the pattern matcher
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case _ => false
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}
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trait CheckableTreeAndTypeAnalysis {
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val typer: Typer
@@ -276,7 +280,7 @@ trait MatchApproximation extends TreeAndTypeAnalysis with ScalaLogic with MatchT
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// hashconsing trees (modulo value-equality)
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def unique(t: Tree, tpOverride: Type = NoType): Tree =
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trees find (a => a.correspondsStructure(t)(sameValue)) match {
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trees find (a => equivalentTree(a, t)) match {
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case Some(orig) =>
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// debug.patmat("unique: "+ (t eq orig, orig))
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orig

‎test/files/pos/t9399.flags

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@@ -0,0 +1 @@
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-Xfatal-warnings

‎test/files/pos/t9399.scala

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sealed abstract class TA
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sealed abstract class TB extends TA
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case object A extends TA
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case object B extends TB
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sealed trait C
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case class CTA(id: Int, da: TA) extends C
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case class CTB(id: Int, da: TB) extends C
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class Test {
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def test(c: C): Unit = c match {
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case CTA(_, A) =>
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case CTA(_, B) =>
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case CTB(_, B) =>
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}
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}
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‎test/files/pos/t9411a.flags

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-Xfatal-warnings

‎test/files/pos/t9411a.scala

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@@ -0,0 +1,27 @@
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object OhNoes {
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sealed trait F
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sealed abstract class FA extends F
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sealed abstract class FB extends F
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case object FA1 extends FA
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case object FB1 extends FB
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case object FB2 extends FB
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sealed trait G
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case object G1 extends G
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case object G2 extends G
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sealed trait H
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case class H1(a: FB, b: G) extends H
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case class H2(a: F) extends H
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val demo: H => Unit = {
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case H1(FB1, G1) =>
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case H1(FB2, G2) =>
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case H2(_: FB) =>
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case H2(_: FA) =>
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case H1(FB1, G2) =>
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case H1(FB2, G1) =>
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}
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}

‎test/files/pos/t9411b.flags

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-Xfatal-warnings

‎test/files/pos/t9411b.scala

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object OhNoes {
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sealed trait F
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sealed abstract class FA extends F
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sealed abstract class FB extends F
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case object FA1 extends FA
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case object FB1 extends FB
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case object FB2 extends FB
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sealed trait G
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case object G1 extends G
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case object G2 extends G
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sealed trait H
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case class H1(a: FB, b: G) extends H
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case class H2(b: F) extends H
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val demo: H => Unit = {
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case H1(FB1, G1) =>
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case H1(FB2, G2) =>
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case H2(_: FB) =>
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case H2(_: FA) =>
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case H1(FB1, G2) =>
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case H1(FB2, G1) =>
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}
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val demo2: H => Unit = {
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case H2(_: FA) =>
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case H2(_: FB) =>
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case H1(FB1, G1) =>
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case H1(FB2, G1) =>
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case H1(FB1, G2) =>
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case H1(FB2, G2) =>
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}
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}

‎test/files/pos/t9630.flags

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-Xfatal-warnings

‎test/files/pos/t9630/t9630a.scala

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sealed trait Base
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final case class Base_1(sameName: Some[Any]) extends Base
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final case class Base_2(sameName: Nested) extends Base
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sealed trait Nested
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final case class Nested_1(x: Any) extends Nested
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final case class Nested_2(y: Any) extends Nested
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