I18628 (#18841)

This PR fixes the minimized test of #18628 that previously runs
infinitely on the global initialization checker.

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -589,7 +589,7 @@ object Objects:
             values.map(ref => ref.widen(height)).join
 
           case Fun(code, thisV, klass, env) =>
-            Fun(code, thisV.widenRefOrCold(height), klass, env.widen(height))
+            Fun(code, thisV.widenRefOrCold(height), klass, env.widen(height - 1))
 
           case ref @ OfClass(klass, outer, _, args, env) =>
             val outer2 = outer.widen(height - 1)

tests/init-global/neg/i18628.scala

@@ -0,0 +1,7 @@
+object Test:
+  class Box(val x: Int)
+
+  def recur(a: => Box, b: => Box): Int =
+    a.x + recur(a, b) + b.x // error // error
+
+  recur(Box(1), Box(2))

tests/init-global/neg/i18628_2.scala

@@ -0,0 +1,7 @@
+object Test:
+  class Box(val x: Int)
+
+  def recur(a: => Box, b: Box): Int =
+    a.x + recur(a, b) + b.x // error
+
+  recur(Box(1), Box(2))

tests/init-global/neg/i18628_3.scala

@@ -0,0 +1,9 @@
+import scala.annotation.init.widen
+
+object Test:
+  class Box(val x: Int)
+
+  def recur(a: => Box, b: => Box): Int =
+    a.x + recur(a: @widen(5), b: @widen(5)) + b.x // error // error
+
+  recur(Box(1), Box(2))

tests/init-global/pos/i18628.scala

@@ -0,0 +1,91 @@
+abstract class Reader[+T] {
+  def first: T
+
+  def rest: Reader[T]
+
+  def atEnd: Boolean
+}
+
+trait Parsers {
+  type Elem
+  type Input = Reader[Elem]
+
+  sealed abstract class ParseResult[+T] {
+    val successful: Boolean
+
+    def map[U](f: T => U): ParseResult[U]
+
+    def flatMapWithNext[U](f: T => Input => ParseResult[U]): ParseResult[U]
+  }
+
+  sealed abstract class NoSuccess(val msg: String) extends ParseResult[Nothing] { // when we don't care about the difference between Failure and Error
+    val successful = false
+
+    def map[U](f: Nothing => U) = this
+
+    def flatMapWithNext[U](f: Nothing => Input => ParseResult[U]): ParseResult[U]
+      = this
+  }
+
+  case class Failure(override val msg: String) extends NoSuccess(msg)
+
+  case class Error(override val msg: String) extends NoSuccess(msg)
+
+  case class Success[+T](result: T, val next: Input) extends ParseResult[T] {
+    val successful = true
+
+    def map[U](f: T => U) = Success(f(result), next)
+
+    def flatMapWithNext[U](f: T => Input => ParseResult[U]): ParseResult[U] = f(result)(next) match {
+      case s @ Success(result, rest) => Success(result, rest)
+      case f: Failure => f
+      case e: Error => e
+    }
+  }
+
+  case class ~[+a, +b](_1: a, _2: b) {
+    override def toString = s"(${_1}~${_2})"
+  }
+
+  abstract class Parser[+T] extends (Input => ParseResult[T]) {
+    def apply(in: Input): ParseResult[T]
+
+    def ~ [U](q: => Parser[U]): Parser[~[T, U]] = {
+      (for(a <- this; b <- q) yield new ~(a,b))
+    }
+
+    def flatMap[U](f: T => Parser[U]): Parser[U]
+      = Parser{ in => this(in) flatMapWithNext(f)}
+
+    def map[U](f: T => U): Parser[U] //= flatMap{x => success(f(x))}
+      = Parser{ in => this(in) map(f)}
+
+    def ^^ [U](f: T => U): Parser[U] = map(f)
+  }
+
+  def Parser[T](f: Input => ParseResult[T]): Parser[T]
+    = new Parser[T]{ def apply(in: Input) = f(in) }
+
+  def accept(e: Elem): Parser[Elem] = acceptIf(_ == e)("'"+e+"' expected but " + _ + " found")
+
+  def acceptIf(p: Elem => Boolean)(err: Elem => String): Parser[Elem] = Parser { in =>
+    if (in.atEnd) Failure("end of input")
+    else if (p(in.first)) Success(in.first, in.rest)
+    else Failure(err(in.first))
+  }
+}
+
+
+object grammars3 extends Parsers {
+  type Elem = String
+
+  val a: Parser[String] = accept("a")
+  val b: Parser[String] = accept("b")
+
+  val AnBnCn: Parser[List[String]] = {
+    repMany(a,b)
+  }
+
+  def repMany[T](p: => Parser[T], q: => Parser[T]): Parser[List[T]] =
+    p~repMany(p,q)~q ^^ {case x~xs~y => x::xs:::(y::Nil)}
+}