From 97bbc243b7cfb6ca9b17dde8803fba7c786e9b8c Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Mon, 12 Aug 2024 15:53:12 +0200
Subject: [PATCH] Use default self type more often

We now also use cap as the default for the self type's capture set if a base class
has an explicit self type, but that type's capture set is universal. This requires
fewer self type annotations.
---
 compiler/src/dotty/tools/dotc/cc/CaptureOps.scala           | 6 ++++--
 compiler/src/dotty/tools/dotc/cc/Setup.scala                | 2 +-
 scala2-library-cc/src/scala/collection/IndexedSeqView.scala | 5 +----
 scala2-library-cc/src/scala/collection/SeqView.scala        | 2 --
 4 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/cc/CaptureOps.scala b/compiler/src/dotty/tools/dotc/cc/CaptureOps.scala
index a2d2d2cf358c..15cdeb9bac11 100644
--- a/compiler/src/dotty/tools/dotc/cc/CaptureOps.scala
+++ b/compiler/src/dotty/tools/dotc/cc/CaptureOps.scala
@@ -528,9 +528,11 @@ extension (cls: ClassSymbol)
                                  // and err on the side of impure.
               && selfType.exists && selfType.captureSet.isAlwaysEmpty
 
-  def baseClassHasExplicitSelfType(using Context): Boolean =
+  def baseClassHasExplicitNonUniversalSelfType(using Context): Boolean =
     cls.baseClasses.exists: bc =>
-      bc.is(CaptureChecked) && bc.givenSelfType.exists
+      bc.is(CaptureChecked)
+      && bc.givenSelfType.exists
+      && !bc.givenSelfType.captureSet.isUniversal
 
   def matchesExplicitRefsInBaseClass(refs: CaptureSet)(using Context): Boolean =
     cls.baseClasses.tail.exists: bc =>
diff --git a/compiler/src/dotty/tools/dotc/cc/Setup.scala b/compiler/src/dotty/tools/dotc/cc/Setup.scala
index 25d50052f107..c0b0d53910fd 100644
--- a/compiler/src/dotty/tools/dotc/cc/Setup.scala
+++ b/compiler/src/dotty/tools/dotc/cc/Setup.scala
@@ -572,7 +572,7 @@ class Setup extends PreRecheck, SymTransformer, SetupAPI:
                 else if cls.isPureClass then
                   // is cls is known to be pure, nothing needs to be added to self type
                   selfInfo
-                else if !cls.isEffectivelySealed && !cls.baseClassHasExplicitSelfType then
+                else if !cls.isEffectivelySealed && !cls.baseClassHasExplicitNonUniversalSelfType then
                   // assume {cap} for completely unconstrained self types of publicly extensible classes
                   CapturingType(cinfo.selfType, CaptureSet.universal)
                 else
diff --git a/scala2-library-cc/src/scala/collection/IndexedSeqView.scala b/scala2-library-cc/src/scala/collection/IndexedSeqView.scala
index 0b6f1bc8e64e..78f8abb8e327 100644
--- a/scala2-library-cc/src/scala/collection/IndexedSeqView.scala
+++ b/scala2-library-cc/src/scala/collection/IndexedSeqView.scala
@@ -16,13 +16,10 @@ package collection
 import scala.annotation.nowarn
 import language.experimental.captureChecking
 
-trait IndexedSeqViewOps[+A, +CC[_], +C] extends Any with SeqViewOps[A, CC, C] {
-  self: IndexedSeqViewOps[A, CC, C]^ =>
-}
+trait IndexedSeqViewOps[+A, +CC[_], +C] extends Any with SeqViewOps[A, CC, C]
 
 /** View defined in terms of indexing a range */
 trait IndexedSeqView[+A] extends IndexedSeqViewOps[A, View, View[A]] with SeqView[A] {
-  self: IndexedSeqView[A]^ =>
 
   override def view: IndexedSeqView[A]^{this} = this
 
diff --git a/scala2-library-cc/src/scala/collection/SeqView.scala b/scala2-library-cc/src/scala/collection/SeqView.scala
index c7af0077ce1a..292dc61ddaa8 100644
--- a/scala2-library-cc/src/scala/collection/SeqView.scala
+++ b/scala2-library-cc/src/scala/collection/SeqView.scala
@@ -25,7 +25,6 @@ import scala.annotation.unchecked.uncheckedCaptures
  *  mapping a SeqView with an impure function gives an impure view).
  */
 trait SeqViewOps[+A, +CC[_], +C] extends Any with IterableOps[A, CC, C] {
-  self: SeqViewOps[A, CC, C]^ =>
 
   def length: Int
   def apply(x: Int): A
@@ -75,7 +74,6 @@ trait SeqViewOps[+A, +CC[_], +C] extends Any with IterableOps[A, CC, C] {
 }
 
 trait SeqView[+A] extends SeqViewOps[A, View, View[A]] with View[A] {
-  self: SeqView[A]^ =>
 
   override def view: SeqView[A]^{this} = this