Syntax change: allow capture sets in infix types

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1492,11 +1492,7 @@ object Parsers {
           else { accept(TLARROW); typ() }
         }
         else if in.token == LBRACE && followingIsCaptureSet() then
-          val refs = inBraces {
-            if in.token == RBRACE then Nil else commaSeparated(captureRef)
-          }
-          val t = typ()
-          CapturingTypeTree(refs, t)
+          CapturingTypeTree(captureSet(), typ())
         else if (in.token == INDENT) enclosed(INDENT, typ())
         else infixType()
 
@@ -1879,8 +1875,14 @@ object Parsers {
     def typeDependingOn(location: Location): Tree =
       if location.inParens then typ()
       else if location.inPattern then rejectWildcardType(refinedType())
+      else if in.token == LBRACE && followingIsCaptureSet() then
+        CapturingTypeTree(captureSet(), infixType())
       else infixType()
 
+    def captureSet(): List[Tree] = inBraces {
+      if in.token == RBRACE then Nil else commaSeparated(captureRef)
+    }
+
 /* ----------- EXPRESSIONS ------------------------------------------------ */
 
     /** Does the current conditional expression continue after
@@ -1950,7 +1952,7 @@ object Parsers {
      *                      |  ‘inline’ InfixExpr MatchClause
      *  Bindings          ::=  `(' [Binding {`,' Binding}] `)'
      *  Binding           ::=  (id | `_') [`:' Type]
-     *  Ascription        ::=  `:' InfixType
+     *  Ascription        ::=  `:' [CaptureSet] InfixType
      *                      |  `:' Annotation {Annotation}
      *                      |  `:' `_' `*'
      *  Catches           ::=  ‘catch’ (Expr | ExprCaseClause)
@@ -3910,7 +3912,7 @@ object Parsers {
       stats.toList
     }
 
-    /** TemplateStatSeq  ::= [id [`:' Type] `=>'] TemplateStat {semi TemplateStat}
+    /** TemplateStatSeq  ::= [SelfType] TemplateStat {semi TemplateStat}
      *  TemplateStat     ::= Import
      *                     | Export
      *                     | Annotations Modifiers Def
@@ -3920,6 +3922,8 @@ object Parsers {
      *                     |
      *  EnumStat         ::= TemplateStat
      *                     | Annotations Modifiers EnumCase
+     *  SelfType         ::= id [‘:’ [CaptureSet] InfixType] ‘=>’
+     *                     | ‘this’ ‘:’ [CaptureSet] InfixType ‘=>’
      */
     def templateStatSeq(): (ValDef, List[Tree]) = checkNoEscapingPlaceholders {
       var self: ValDef = EmptyValDef

tests/disabled/pos/lazylist.scala

@@ -1,7 +1,7 @@
 package lazylists
 
 abstract class LazyList[+T]:
-  this: ({*} LazyList[T]) =>
+  this: {*} LazyList[T] =>
 
   def isEmpty: Boolean
   def head: T

tests/pos-custom-args/captures/classes.scala

@@ -1,15 +1,15 @@
 class B
 type Cap = {*} B
 class C(val n: Cap):
-  this: ({n} C) =>
+  this: {n} C =>
   def foo(): {n} B = n
 
 
 def test(x: Cap, y: Cap, z: Cap) =
   val c0 = C(x)
   val c1: {x} C {val n: {x} B} = c0
   val d = c1.foo()
-  d: ({x} B)
+  d: {x} B
 
   val c2 = if ??? then C(x) else C(y)
   val c2a = identity(c2)

tests/pos-custom-args/captures/iterators.scala

@@ -1,7 +1,7 @@
 package cctest
 
 abstract class Iterator[T]:
-  thisIterator: ({*} Iterator[T]) =>
+  thisIterator: {*} Iterator[T] =>
 
   def hasNext: Boolean
   def next: T

tests/pos-custom-args/captures/lazylists.scala

@@ -2,7 +2,7 @@ class CC
 type Cap = {*} CC
 
 trait LazyList[+A]:
-  this: ({*} LazyList[A]) =>
+  this: {*} LazyList[A] =>
 
   def isEmpty: Boolean
   def head: A
@@ -16,12 +16,12 @@ object LazyNil extends LazyList[Nothing]:
 extension [A](xs: {*} LazyList[A])
   def map[B](f: A => B): {xs, f} LazyList[B] =
     final class Mapped extends LazyList[B]:
-      this: ({xs, f} Mapped) =>
+      this: {xs, f} Mapped =>
 
       def isEmpty = false
       def head: B = f(xs.head)
       def tail: {this} LazyList[B] = xs.tail.map(f)  // OK
-      def concat(other: {f} LazyList[A]): {this, f} LazyList[A] = ??? : ({xs, f} LazyList[A]) // OK
+      def concat(other: {f} LazyList[A]): {this, f} LazyList[A] = ??? : {xs, f} LazyList[A] // OK
     if xs.isEmpty then LazyNil
     else new Mapped
 
@@ -31,7 +31,7 @@ def test(cap1: Cap, cap2: Cap) =
 
   val xs =
     class Initial extends LazyList[String]:
-      this: ({cap1} Initial) =>
+      this: {cap1} Initial =>
 
       def isEmpty = false
       def head = f("")

tests/pos-custom-args/captures/lazylists1.scala

@@ -2,7 +2,7 @@ class CC
 type Cap = {*} CC
 
 trait LazyList[+A]:
-  this: ({*} LazyList[A]) =>
+  this: {*} LazyList[A] =>
 
   def isEmpty: Boolean
   def head: A
@@ -14,7 +14,7 @@ object LazyNil extends LazyList[Nothing]:
   def tail = ???
 
 final class LazyCons[+T](val x: T, val xs: Int => {*} LazyList[T]) extends LazyList[T]:
-  this: ({*} LazyList[T]) =>
+  this: {*} LazyList[T] =>
 
   def isEmpty = false
   def head = x