From 96d507367612e5f68266b4ecd656301a408b1fc0 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Tue, 1 Dec 2020 11:29:13 +0100
Subject: [PATCH] Fix #10573: Devirtualize member selection when matching

---
 .../scala/quoted/runtime/impl/Matcher.scala   | 21 +++++++++++++------
 .../quoted/runtime/impl/QuotesImpl.scala      |  3 +++
 library/src/scala/quoted/Quotes.scala         |  6 ++++++
 tests/pos-macros/i10573/Macro_1.scala         | 16 ++++++++++++++
 tests/pos-macros/i10573/Test_2.scala          |  2 ++
 5 files changed, 42 insertions(+), 6 deletions(-)
 create mode 100644 tests/pos-macros/i10573/Macro_1.scala
 create mode 100644 tests/pos-macros/i10573/Test_2.scala

diff --git a/compiler/src/scala/quoted/runtime/impl/Matcher.scala b/compiler/src/scala/quoted/runtime/impl/Matcher.scala
index 21fb5bb6d74f..89086df98156 100644
--- a/compiler/src/scala/quoted/runtime/impl/Matcher.scala
+++ b/compiler/src/scala/quoted/runtime/impl/Matcher.scala
@@ -231,7 +231,7 @@ object Matcher {
             scrutinee =?= expr2
 
           /* Match selection */
-          case (ref: Ref, Select(qual2, _)) if symbolMatch(scrutinee.symbol, pattern.symbol) =>
+          case (ref: Ref, Select(qual2, _)) if symbolMatch(scrutinee, pattern) =>
             ref match
               case Select(qual1, _) => qual1 =?= qual2
               case ref: Ident =>
@@ -240,7 +240,7 @@ object Matcher {
                   case _ => matched
 
           /* Match reference */
-          case (_: Ref, _: Ident) if symbolMatch(scrutinee.symbol, pattern.symbol) =>
+          case (_: Ref, _: Ident) if symbolMatch(scrutinee, pattern) =>
             matched
 
           /* Match application */
@@ -348,10 +348,19 @@ object Matcher {
      *   - The scrutinee has is in the environment and they are equivalent
      *   - The scrutinee overrides the symbol of the pattern
      */
-    private def symbolMatch(scrutinee: Symbol, pattern: Symbol)(using Env): Boolean =
-      scrutinee == pattern
-      || summon[Env].get(scrutinee).contains(pattern)
-      || scrutinee.allOverriddenSymbols.contains(pattern)
+    private def symbolMatch(scrutineeTree: Tree, patternTree: Tree)(using Env): Boolean =
+      val scrutinee = scrutineeTree.symbol
+      val devirtualizedScrutinee = scrutineeTree match
+        case Select(qual, _) =>
+          val sym = scrutinee.overridingSymbol(qual.tpe.typeSymbol)
+          if sym.exists then sym
+          else scrutinee
+        case _ => scrutinee
+      val pattern = patternTree.symbol
+
+      devirtualizedScrutinee == pattern
+      || summon[Env].get(devirtualizedScrutinee).contains(pattern)
+      || devirtualizedScrutinee.allOverriddenSymbols.contains(pattern)
 
     private object ClosedPatternTerm {
       /** Matches a term that does not contain free variables defined in the pattern (i.e. not defined in `Env`) */
diff --git a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
index 6e197f5462fc..cd6f94458eb7 100644
--- a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
+++ b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
@@ -2349,6 +2349,9 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         def paramSymss: List[List[Symbol]] = self.denot.paramSymss
         def primaryConstructor: Symbol = self.denot.primaryConstructor
         def allOverriddenSymbols: Iterator[Symbol] = self.denot.allOverriddenSymbols
+        def overridingSymbol(ofclazz: Symbol): Symbol =
+          if ofclazz.isClass then self.denot.overridingSymbol(ofclazz.asClass)
+          else dotc.core.Symbols.NoSymbol
 
         def caseFields: List[Symbol] =
           if !self.isClass then Nil
diff --git a/library/src/scala/quoted/Quotes.scala b/library/src/scala/quoted/Quotes.scala
index a8dd2317e5d8..4c0f1bdb6d96 100644
--- a/library/src/scala/quoted/Quotes.scala
+++ b/library/src/scala/quoted/Quotes.scala
@@ -3624,6 +3624,12 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
         /** Returns all symbols overridden by this symbol. */
         def allOverriddenSymbols: Iterator[Symbol]
 
+        /** The symbol overriding this symbol in given subclass `ofclazz`.
+         *
+         *  @param ofclazz is a subclass of this symbol's owner
+         */
+        def overridingSymbol(ofclazz: Symbol): Symbol
+
         /** The primary constructor of a class or trait, `noSymbol` if not applicable. */
         def primaryConstructor: Symbol
 
diff --git a/tests/pos-macros/i10573/Macro_1.scala b/tests/pos-macros/i10573/Macro_1.scala
new file mode 100644
index 000000000000..7c49a8e5ca13
--- /dev/null
+++ b/tests/pos-macros/i10573/Macro_1.scala
@@ -0,0 +1,16 @@
+import scala.quoted._
+
+
+trait A { def foo: Int }
+class B extends A { def foo: Int = 1 }
+
+inline def test(): Unit = ${ testExpr() }
+
+def testExpr()(using Quotes): Expr[Unit] = {
+  val e0: Expr[A] = '{ new B }
+  val e1: Expr[Int] = '{ $e0.foo }
+  e1 match
+    case '{ ($x: B).foo } => '{ val b: B = $x; () }
+    case _ => quotes.reflect.report.throwError("did not match")
+}
+
diff --git a/tests/pos-macros/i10573/Test_2.scala b/tests/pos-macros/i10573/Test_2.scala
new file mode 100644
index 000000000000..1e5f437d6bd9
--- /dev/null
+++ b/tests/pos-macros/i10573/Test_2.scala
@@ -0,0 +1,2 @@
+
+def Test = test()