From c3bce867da033c325ec728b793dd76dee43d2d81 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Fri, 23 Aug 2019 18:14:57 +0200
Subject: [PATCH 1/4] Fix #7084: Drop revealProtoOfExtMethod

Don't call `revealProtoOfExtMethod` wehn constraining results in adaptation.
Revealing the proottype too early disables further implicit searches, as is
demonstrated by i7084.scala. The original reason to have `revealProtoOfExtMethod`
was to typecheck i5773a. But it looks like this is no longer valid. i5773a
now compiles regardless.
---
 compiler/src/dotty/tools/dotc/typer/Typer.scala | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 892ef2a15d93..4c03c679e5ee 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -2485,13 +2485,6 @@ class Typer extends Namer
       }
     }
 
-    /** Reveal ignored parts of prototype when synthesizing the receiver
-     *  of an extension method. This is necessary for pos/i5773a.scala
-     */
-    def revealProtoOfExtMethod(tp: Type)(implicit ctx: Context): Type =
-      if (ctx.mode.is(Mode.SynthesizeExtMethodReceiver)) tp.deepenProto
-      else tp
-
     def adaptNoArgsImplicitMethod(wtp: MethodType): Tree = {
       assert(wtp.isImplicitMethod)
       val tvarsToInstantiate = tvarsInParams(tree, locked).distinct
@@ -2512,7 +2505,7 @@ class Typer extends Namer
             arg.tpe match {
               case failed: AmbiguousImplicits =>
                 val pt1 = pt.deepenProto
-                if ((pt1 `ne` pt) && resultMatches(wtp, pt1)) implicitArgs(formals, argIndex, pt1)
+                if ((pt1 `ne` pt) && constrainResult(tree.symbol, wtp, pt1)) implicitArgs(formals, argIndex, pt1)
                 else arg :: implicitArgs(formals1, argIndex + 1, pt1)
               case failed: SearchFailureType if !tree.symbol.hasDefaultParams =>
                 // no need to search further, the adapt fails in any case
@@ -2742,9 +2735,6 @@ class Typer extends Namer
       case _ => tp
     }
 
-    def resultMatches(wtp: Type, pt: Type) =
-      constrainResult(tree.symbol, wtp, revealProtoOfExtMethod(pt))
-
     def adaptNoArgs(wtp: Type): Tree = {
       val ptNorm = underlyingApplied(pt)
       def functionExpected = defn.isFunctionType(ptNorm)
@@ -2758,7 +2748,7 @@ class Typer extends Namer
         case wtp: ExprType =>
           readaptSimplified(tree.withType(wtp.resultType))
         case wtp: MethodType if wtp.isImplicitMethod &&
-          ({ resMatch = resultMatches(wtp, pt); resMatch } || !functionExpected) =>
+          ({ resMatch = constrainResult(tree.symbol, wtp, pt); resMatch } || !functionExpected) =>
           if (resMatch || ctx.mode.is(Mode.ImplicitsEnabled))
             adaptNoArgsImplicitMethod(wtp)
           else {

From 2ea76939964fd4c5525ea29cc8687c1d29e3d308 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Fri, 23 Aug 2019 18:21:47 +0200
Subject: [PATCH 2/4] Add test

---
 tests/pos/i7084.scala | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 tests/pos/i7084.scala

diff --git a/tests/pos/i7084.scala b/tests/pos/i7084.scala
new file mode 100644
index 000000000000..82befa148529
--- /dev/null
+++ b/tests/pos/i7084.scala
@@ -0,0 +1,15 @@
+object Test {
+
+  type Foo
+
+  given A {
+    def (y: Any) g given Foo: Any = ???
+  }
+
+  def f(x: Any) given Foo: Any = {
+    val y = x.g
+    y.g
+
+    x.g.g
+  }
+}
\ No newline at end of file

From bf8455461e87908c6613f5a50c6645be2fce5634 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sat, 24 Aug 2019 12:34:24 +0200
Subject: [PATCH 3/4] Test for #7087

---
 tests/pos/i7087.scala | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 tests/pos/i7087.scala

diff --git a/tests/pos/i7087.scala b/tests/pos/i7087.scala
new file mode 100644
index 000000000000..96298e31fdf0
--- /dev/null
+++ b/tests/pos/i7087.scala
@@ -0,0 +1,13 @@
+type Foo
+
+type G[A]
+
+type F[T] = T match {
+  case G[a] => String
+}
+
+given A {
+  def (tup: T) g[T] given (Foo: F[T]) = ???
+}
+
+def f(x: G[Int]) given (Foo: String) = x.g
\ No newline at end of file

From 61f15bc1a879ad7e2175f083d133f74e0b80dbc3 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sat, 24 Aug 2019 19:43:35 +0200
Subject: [PATCH 4/4] Blacklist i7087 for pickling and from-tasty tests

We get in both cases a type difference where one side is an unreduced match type
and the other side is its redux.
---
 compiler/test/dotc/pos-from-tasty.blacklist    | 3 +++
 compiler/test/dotc/pos-test-pickling.blacklist | 1 +
 2 files changed, 4 insertions(+)

diff --git a/compiler/test/dotc/pos-from-tasty.blacklist b/compiler/test/dotc/pos-from-tasty.blacklist
index 1c1b2e32e86c..f3a7568dcf01 100644
--- a/compiler/test/dotc/pos-from-tasty.blacklist
+++ b/compiler/test/dotc/pos-from-tasty.blacklist
@@ -6,3 +6,6 @@ t3612.scala
 
 # Other failure
 t802.scala
+
+# Matchtype
+i7087.scala
\ No newline at end of file
diff --git a/compiler/test/dotc/pos-test-pickling.blacklist b/compiler/test/dotc/pos-test-pickling.blacklist
index b1068027c9f1..88bd35eb12f4 100644
--- a/compiler/test/dotc/pos-test-pickling.blacklist
+++ b/compiler/test/dotc/pos-test-pickling.blacklist
@@ -21,6 +21,7 @@ i939.scala
 typelevel0.scala
 matchtype.scala
 6322.scala
+i7087.scala
 
 # Opaque type
 i5720.scala