SI-9630 Fix spurious warning related to same-named case accessors [backport]

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.

(cherry picked from commit 79a52e6807d2797dee12bab1730765441a0e222d)

11 files changed, 112 insertions, 7 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala b/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala
index 91777b34d5..40fcceb0bf 100644
--- a/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala
+++ b/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala
@@ -691,7 +691,7 @@ trait ScalaLogic extends Interface with Logic with TreeAndTypeAnalysis {
           // if X is mutable.
           freshExistentialSubtype(t.tpe)
         }
-        else trees find (a => a.correspondsStructure(t)(sameValue)) match {
+        else trees find (a => equivalentTree(a, t)) match {
           case Some(orig) =>
             debug.patmat("unique tp for tree: " + ((orig, orig.tpe)))
             orig.tpe
diff --git a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
index 1331eb6993..c71299b893 100644
--- a/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
+++ b/src/compiler/scala/tools/nsc/transform/patmat/MatchAnalysis.scala
@@ -85,11 +85,15 @@ trait TreeAndTypeAnalysis extends Debugging {
     tp <:< tpImpliedNormalizedToAny
   }
 
-  // TODO: improve, e.g., for constants
-  def sameValue(a: Tree, b: Tree): Boolean = (a eq b) || ((a, b) match {
-    case (_ : Ident, _ : Ident) => a.symbol eq b.symbol
-    case _                      => false
-  })
+  def equivalentTree(a: Tree, b: Tree): Boolean = (a, b) match {
+    case (Select(qual1, _), Select(qual2, _)) => equivalentTree(qual1, qual2) && a.symbol == b.symbol
+    case (Ident(_), Ident(_)) => a.symbol == b.symbol
+    case (Literal(c1), Literal(c2)) => c1 == c2
+    case (This(_), This(_)) => a.symbol == b.symbol
+    case (Apply(fun1, args1), Apply(fun2, args2)) => equivalentTree(fun1, fun2) && args1.corresponds(args2)(equivalentTree)
+    // Those are the only cases we need to handle in the pattern matcher
+    case _ => false
+  }
 
   trait CheckableTreeAndTypeAnalysis {
     val typer: Typer
@@ -277,7 +281,7 @@ trait MatchApproximation extends TreeAndTypeAnalysis with ScalaLogic with MatchT
 
       // hashconsing trees (modulo value-equality)
       def unique(t: Tree, tpOverride: Type = NoType): Tree =
-        trees find (a => a.correspondsStructure(t)(sameValue)) match {
+        trees find (a => equivalentTree(a, t)) match {
           case Some(orig) =>
             // debug.patmat("unique: "+ (t eq orig, orig))
             orig
diff --git a/test/files/pos/t9399.flags b/test/files/pos/t9399.flags
new file mode 100644
index 0000000000..85d8eb2ba2
--- /dev/null
+++ b/test/files/pos/t9399.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
diff --git a/test/files/pos/t9399.scala b/test/files/pos/t9399.scala
new file mode 100644
index 0000000000..e8a8720f94
--- /dev/null
+++ b/test/files/pos/t9399.scala
@@ -0,0 +1,17 @@
+sealed abstract class TA
+sealed abstract class TB extends TA
+case object A extends TA
+case object B extends TB
+
+sealed trait C
+case class CTA(id: Int, da: TA) extends C
+case class CTB(id: Int, da: TB) extends C
+
+class Test {
+  def test(c: C): Unit = c match {
+    case CTA(_, A) =>
+    case CTA(_, B) =>
+    case CTB(_, B) =>
+  }
+}
+
diff --git a/test/files/pos/t9411a.flags b/test/files/pos/t9411a.flags
new file mode 100644
index 0000000000..85d8eb2ba2
--- /dev/null
+++ b/test/files/pos/t9411a.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
diff --git a/test/files/pos/t9411a.scala b/test/files/pos/t9411a.scala
new file mode 100644
index 0000000000..d5264663ec
--- /dev/null
+++ b/test/files/pos/t9411a.scala
@@ -0,0 +1,27 @@
+object OhNoes {
+
+  sealed trait F
+  sealed abstract class FA extends F
+  sealed abstract class FB extends F
+
+  case object FA1 extends FA
+  case object FB1 extends FB
+  case object FB2 extends FB
+
+  sealed trait G
+  case object G1 extends G
+  case object G2 extends G
+
+  sealed trait H
+  case class H1(a: FB, b: G) extends H
+  case class H2(a: F)        extends H
+
+  val demo: H => Unit = {
+    case H1(FB1, G1) =>
+    case H1(FB2, G2) =>
+    case H2(_: FB) =>
+    case H2(_: FA) =>
+    case H1(FB1, G2) =>
+    case H1(FB2, G1) =>
+  }
+}
diff --git a/test/files/pos/t9411b.flags b/test/files/pos/t9411b.flags
new file mode 100644
index 0000000000..85d8eb2ba2
--- /dev/null
+++ b/test/files/pos/t9411b.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
diff --git a/test/files/pos/t9411b.scala b/test/files/pos/t9411b.scala
new file mode 100644
index 0000000000..6888ba9382
--- /dev/null
+++ b/test/files/pos/t9411b.scala
@@ -0,0 +1,36 @@
+object OhNoes {
+
+  sealed trait F
+  sealed abstract class FA extends F
+  sealed abstract class FB extends F
+
+  case object FA1 extends FA
+  case object FB1 extends FB
+  case object FB2 extends FB
+
+  sealed trait G
+  case object G1 extends G
+  case object G2 extends G
+
+  sealed trait H
+  case class H1(a: FB, b: G) extends H
+  case class H2(b: F)        extends H
+
+  val demo: H => Unit = {
+    case H1(FB1, G1) =>
+    case H1(FB2, G2) =>
+    case H2(_: FB) =>
+    case H2(_: FA) =>
+    case H1(FB1, G2) =>
+    case H1(FB2, G1) =>
+  }
+
+  val demo2: H => Unit = {
+    case H2(_: FA) =>
+    case H2(_: FB) =>
+    case H1(FB1, G1) =>
+    case H1(FB2, G1) =>
+    case H1(FB1, G2) =>
+    case H1(FB2, G2) =>
+  }
+}
diff --git a/test/files/pos/t9630.flags b/test/files/pos/t9630.flags
new file mode 100644
index 0000000000..85d8eb2ba2
--- /dev/null
+++ b/test/files/pos/t9630.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
diff --git a/test/files/pos/t9630/t9630a.scala b/test/files/pos/t9630/t9630a.scala
new file mode 100644
index 0000000000..c76ecd2ff2
--- /dev/null
+++ b/test/files/pos/t9630/t9630a.scala
@@ -0,0 +1,9 @@
+
+sealed trait Base
+final case class Base_1(sameName: Some[Any]) extends Base
+final case class Base_2(sameName: Nested) extends Base
+
+sealed trait Nested
+final case class Nested_1(x: Any) extends Nested
+final case class Nested_2(y: Any) extends Nested
+
diff --git a/test/files/pos/t9630/t9630b.scala b/test/files/pos/t9630/t9630b.scala
new file mode 100644
index 0000000000..3e1787ec52
--- /dev/null
+++ b/test/files/pos/t9630/t9630b.scala
@@ -0,0 +1,8 @@
+
+class Test {
+  def test(b: Base): Unit = b match {
+    case Base_1(Some(_)) =>
+    case Base_2(Nested_1(_)) =>
+    case Base_2(Nested_2(_)) =>
+  }
+}