diff --git a/community-build/community-projects/specs2 b/community-build/community-projects/specs2 index e42f7987b4ce..ba01cca013d9 160000 --- a/community-build/community-projects/specs2 +++ b/community-build/community-projects/specs2 @@ -1 +1 @@ -Subproject commit e42f7987b4ce30d95fca3f30b9d508021f2fdac7 +Subproject commit ba01cca013d9d99e390d17619664bdedd716e0d7 diff --git a/compiler/src/dotty/tools/dotc/config/Feature.scala b/compiler/src/dotty/tools/dotc/config/Feature.scala index fa262a5880ff..cdd83b15f4fc 100644 --- a/compiler/src/dotty/tools/dotc/config/Feature.scala +++ b/compiler/src/dotty/tools/dotc/config/Feature.scala @@ -33,6 +33,7 @@ object Feature: val pureFunctions = experimental("pureFunctions") val captureChecking = experimental("captureChecking") val into = experimental("into") + val givenLoopPrevention = experimental("givenLoopPrevention") val globalOnlyImports: Set[TermName] = Set(pureFunctions, captureChecking) diff --git a/compiler/src/dotty/tools/dotc/typer/Implicits.scala b/compiler/src/dotty/tools/dotc/typer/Implicits.scala index ff23e8180f1c..1672c94fd969 100644 --- a/compiler/src/dotty/tools/dotc/typer/Implicits.scala +++ b/compiler/src/dotty/tools/dotc/typer/Implicits.scala @@ -26,8 +26,8 @@ import Scopes.newScope import Typer.BindingPrec, BindingPrec.* import Hashable.* import util.{EqHashMap, Stats} -import config.{Config, Feature} -import Feature.migrateTo3 +import config.{Config, Feature, SourceVersion} +import Feature.{migrateTo3, sourceVersion} import config.Printers.{implicits, implicitsDetailed} import collection.mutable import reporting.* @@ -324,7 +324,7 @@ object Implicits: /** Is this the outermost implicits? This is the case if it either the implicits * of NoContext, or the last one before it. */ - private def isOuterMost = { + private def isOutermost = { val finalImplicits = NoContext.implicits (this eq finalImplicits) || (outerImplicits eqn finalImplicits) } @@ -356,7 +356,7 @@ object Implicits: Stats.record("uncached eligible") if monitored then record(s"check uncached eligible refs in irefCtx", refs.length) val ownEligible = filterMatching(tp) - if isOuterMost then ownEligible + if isOutermost then ownEligible else combineEligibles(ownEligible, outerImplicits.nn.uncachedEligible(tp)) /** The implicit references that are eligible for type `tp`. */ @@ -383,7 +383,7 @@ object Implicits: private def computeEligible(tp: Type): List[Candidate] = /*>|>*/ trace(i"computeEligible $tp in $refs%, %", implicitsDetailed) /*<|<*/ { if (monitored) record(s"check eligible refs in irefCtx", refs.length) val ownEligible = filterMatching(tp) - if isOuterMost then ownEligible + if isOutermost then ownEligible else combineEligibles(ownEligible, outerImplicits.nn.eligible(tp)) } @@ -392,7 +392,7 @@ object Implicits: override def toString: String = { val own = i"(implicits: $refs%, %)" - if (isOuterMost) own else own + "\n " + outerImplicits + if (isOutermost) own else own + "\n " + outerImplicits } /** This context, or a copy, ensuring root import from symbol `root` @@ -1550,11 +1550,15 @@ trait Implicits: case _ => tp.isAny || tp.isAnyRef - private def searchImplicit(contextual: Boolean): SearchResult = + /** Search implicit in context `ctxImplicits` or else in implicit scope + * of expected type if `ctxImplicits == null`. + */ + private def searchImplicit(ctxImplicits: ContextualImplicits | Null): SearchResult = if isUnderspecified(wildProto) then SearchFailure(TooUnspecific(pt), span) else - val eligible = + val contextual = ctxImplicits != null + val preEligible = // the eligible candidates, ignoring positions if contextual then if ctx.gadt.isNarrowing then withoutMode(Mode.ImplicitsEnabled) { @@ -1562,22 +1566,101 @@ trait Implicits: } else ctx.implicits.eligible(wildProto) else implicitScope(wildProto).eligible - searchImplicit(eligible, contextual) match + + /** Does candidate `cand` come too late for it to be considered as an + * eligible candidate? This is the case if `cand` appears in the same + * scope as a given definition of the form `given ... = ...` that + * encloses the search point and `cand` comes later in the source or + * coincides with that given definition. + */ + def comesTooLate(cand: Candidate): Boolean = + val candSym = cand.ref.symbol + def candSucceedsGiven(sym: Symbol): Boolean = + val owner = sym.owner + if owner == candSym.owner then + sym.is(GivenVal) && sym.span.exists && sym.span.start <= candSym.span.start + else if owner.isClass then false + else candSucceedsGiven(owner) + + ctx.isTyper + && !candSym.isOneOf(TermParamOrAccessor | Synthetic) + && candSym.span.exists + && candSucceedsGiven(ctx.owner) + end comesTooLate + + val eligible = // the eligible candidates that come before the search point + if contextual && sourceVersion.isAtLeast(SourceVersion.`3.4`) + then preEligible.filterNot(comesTooLate) + else preEligible + + def checkResolutionChange(result: SearchResult) = + if (eligible ne preEligible) + && !Feature.enabled(Feature.givenLoopPrevention) + then + val prevResult = searchImplicit(preEligible, contextual) + prevResult match + case prevResult: SearchSuccess => + def remedy = pt match + case _: SelectionProto => + "conversion,\n - use an import to get extension method into scope" + case _: ViewProto => + "conversion" + case _ => + "argument" + + def showResult(r: SearchResult) = r match + case r: SearchSuccess => ctx.printer.toTextRef(r.ref).show + case r => r.show + + result match + case result: SearchSuccess if prevResult.ref frozen_=:= result.ref => + // OK + case _ => + val msg = + em"""Result of implicit search for $pt will change. + |Current result ${showResult(prevResult)} will be no longer eligible + | because it is not defined before the search position. + |Result with new rules: ${showResult(result)}. + |To opt into the new rules, use the `experimental.givenLoopPrevention` language import. + | + |To fix the problem without the language import, you could try one of the following: + | - use a `given ... with` clause as the enclosing given, + | - rearrange definitions so that ${showResult(prevResult)} comes earlier, + | - use an explicit $remedy.""" + if sourceVersion.isAtLeast(SourceVersion.`3.5`) + then report.error(msg, srcPos) + else report.warning(msg.append("\nThis will be an error in Scala 3.5 and later."), srcPos) + case _ => + prevResult + else result + end checkResolutionChange + + val result = searchImplicit(eligible, contextual) + result match case result: SearchSuccess => - result + checkResolutionChange(result) case failure: SearchFailure => failure.reason match case _: AmbiguousImplicits => failure case reason => if contextual then - searchImplicit(contextual = false).recoverWith { - failure2 => failure2.reason match - case _: AmbiguousImplicits => failure2 - case _ => - reason match - case (_: DivergingImplicit) => failure - case _ => List(failure, failure2).maxBy(_.tree.treeSize) - } + // If we filtered out some candidates for being too late, we should + // do another contextual search further out, since the dropped candidates + // might have shadowed an eligible candidate in an outer level. + // Otherwise, proceed with a search of the implicit scope. + val newCtxImplicits = + if eligible eq preEligible then null + else ctxImplicits.nn.outerImplicits: ContextualImplicits | Null + // !!! Dotty problem: without the ContextualImplicits | Null type ascription + // we get a Ycheck failure after arrayConstructors due to "Types differ" + checkResolutionChange: + searchImplicit(newCtxImplicits).recoverWith: + failure2 => failure2.reason match + case _: AmbiguousImplicits => failure2 + case _ => + reason match + case (_: DivergingImplicit) => failure + case _ => List(failure, failure2).maxBy(_.tree.treeSize) else failure end searchImplicit @@ -1595,7 +1678,7 @@ trait Implicits: case ref: TermRef => SearchSuccess(tpd.ref(ref).withSpan(span.startPos), ref, 0)(ctx.typerState, ctx.gadt) case _ => - searchImplicit(contextual = true) + searchImplicit(ctx.implicits) end bestImplicit def implicitScope(tp: Type): OfTypeImplicits = ctx.run.nn.implicitScope(tp) diff --git a/docs/_docs/reference/changed-features/implicit-resolution.md b/docs/_docs/reference/changed-features/implicit-resolution.md index 6a898690b565..861a63bd4a05 100644 --- a/docs/_docs/reference/changed-features/implicit-resolution.md +++ b/docs/_docs/reference/changed-features/implicit-resolution.md @@ -163,8 +163,4 @@ The new rules are as follows: An implicit `a` defined in `A` is more specific th Condition (*) is new. It is necessary to ensure that the defined relation is transitive. - - - - [//]: # todo: expand with precise rules diff --git a/docs/_docs/reference/experimental/given-loop-prevention.md b/docs/_docs/reference/experimental/given-loop-prevention.md new file mode 100644 index 000000000000..e306ba977d45 --- /dev/null +++ b/docs/_docs/reference/experimental/given-loop-prevention.md @@ -0,0 +1,31 @@ +--- +layout: doc-page +title: Given Loop Prevention +redirectFrom: /docs/reference/other-new-features/into-modifier.html +nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/into-modifier.html +--- + +Implicit resolution now avoids generating recursive givens that can lead to an infinite loop at runtime. Here is an example: + +```scala +object Prices { + opaque type Price = BigDecimal + + object Price{ + given Ordering[Price] = summon[Ordering[BigDecimal]] // was error, now avoided + } +} +``` + +Previously, implicit resolution would resolve the `summon` to the given in `Price`, leading to an infinite loop (a warning was issued in that case). We now use the underlying given in `BigDecimal` instead. We achieve that by adding the following rule for implicit search: + + - When doing an implicit search while checking the implementation of a `given` definition `G` of the form + ``` + given ... = .... + ``` + discard all search results that lead back to `G` or to a given with the same owner as `G` that comes later in the source than `G`. + +The new behavior is enabled with the `experimental.givenLoopPrevention` language import. If no such import or setting is given, a warning is issued where the behavior would change under that import (for source version 3.4 and later). + +Old-style implicit definitions are unaffected by this change. + diff --git a/docs/sidebar.yml b/docs/sidebar.yml index 65d7ac2f9ee4..d9f86d5141c3 100644 --- a/docs/sidebar.yml +++ b/docs/sidebar.yml @@ -153,6 +153,7 @@ subsection: - page: reference/experimental/cc.md - page: reference/experimental/purefuns.md - page: reference/experimental/tupled-function.md + - page: reference/experimental/given-loop-prevention.md - page: reference/syntax.md - title: Language Versions index: reference/language-versions/language-versions.md diff --git a/library/src/scala/runtime/stdLibPatches/language.scala b/library/src/scala/runtime/stdLibPatches/language.scala index c37555f26653..ae323befa1a4 100644 --- a/library/src/scala/runtime/stdLibPatches/language.scala +++ b/library/src/scala/runtime/stdLibPatches/language.scala @@ -91,6 +91,15 @@ object language: @compileTimeOnly("`into` can only be used at compile time in import statements") object into + /** Experimental support for new given resolution rules that avoid looping + * givens. By the new rules, a given may not implicitly use itself or givens + * defined after it. + * + * @see [[https://dotty.epfl.ch/docs/reference/experimental/given-loop-prevention]] + */ + @compileTimeOnly("`givenLoopPrevention` can only be used at compile time in import statements") + object givenLoopPrevention + /** Was needed to add support for relaxed imports of extension methods. * The language import is no longer needed as this is now a standard feature since SIP was accepted. * @see [[http://dotty.epfl.ch/docs/reference/contextual/extension-methods]] diff --git a/tests/neg/i15474.check b/tests/neg/i15474.check new file mode 100644 index 000000000000..6a60aed304aa --- /dev/null +++ b/tests/neg/i15474.check @@ -0,0 +1,29 @@ +-- Error: tests/neg/i15474.scala:6:39 ---------------------------------------------------------------------------------- +6 | given c: Conversion[ String, Int ] = _.toInt // error + | ^ + | Result of implicit search for ?{ toInt: ? } will change. + | Current result Test2.c will be no longer eligible + | because it is not defined before the search position. + | Result with new rules: augmentString. + | To opt into the new rules, use the `experimental.givenLoopPrevention` language import. + | + | To fix the problem without the language import, you could try one of the following: + | - use a `given ... with` clause as the enclosing given, + | - rearrange definitions so that Test2.c comes earlier, + | - use an explicit conversion, + | - use an import to get extension method into scope. + | This will be an error in Scala 3.5 and later. +-- Error: tests/neg/i15474.scala:12:56 --------------------------------------------------------------------------------- +12 | given Ordering[Price] = summon[Ordering[BigDecimal]] // error + | ^ + | Result of implicit search for Ordering[BigDecimal] will change. + | Current result Prices.Price.given_Ordering_Price will be no longer eligible + | because it is not defined before the search position. + | Result with new rules: scala.math.Ordering.BigDecimal. + | To opt into the new rules, use the `experimental.givenLoopPrevention` language import. + | + | To fix the problem without the language import, you could try one of the following: + | - use a `given ... with` clause as the enclosing given, + | - rearrange definitions so that Prices.Price.given_Ordering_Price comes earlier, + | - use an explicit argument. + | This will be an error in Scala 3.5 and later. diff --git a/tests/neg/i15474.scala b/tests/neg/i15474.scala index 8edf97a1e55a..b196d1b400ef 100644 --- a/tests/neg/i15474.scala +++ b/tests/neg/i15474.scala @@ -2,12 +2,8 @@ import scala.language.implicitConversions -object Test1: - given c: Conversion[ String, Int ] with - def apply(from: String): Int = from.toInt // error - object Test2: - given c: Conversion[ String, Int ] = _.toInt // loop not detected, could be used as a fallback to avoid the warning. + given c: Conversion[ String, Int ] = _.toInt // error object Prices { opaque type Price = BigDecimal @@ -15,4 +11,6 @@ object Prices { object Price{ given Ordering[Price] = summon[Ordering[BigDecimal]] // error } -} \ No newline at end of file +} + + diff --git a/tests/neg/i15474b.check b/tests/neg/i15474b.check new file mode 100644 index 000000000000..73ef720af7e3 --- /dev/null +++ b/tests/neg/i15474b.check @@ -0,0 +1,5 @@ +-- Error: tests/neg/i15474b.scala:7:40 --------------------------------------------------------------------------------- +7 | def apply(from: String): Int = from.toInt // error: infinite loop in function body + | ^^^^^^^^^^ + | Infinite loop in function body + | Test1.c.apply(from).toInt diff --git a/tests/neg/i15474b.scala b/tests/neg/i15474b.scala new file mode 100644 index 000000000000..9d496c37ef00 --- /dev/null +++ b/tests/neg/i15474b.scala @@ -0,0 +1,8 @@ +//> using options -Xfatal-warnings + +import scala.language.implicitConversions + +object Test1: + given c: Conversion[ String, Int ] with + def apply(from: String): Int = from.toInt // error: infinite loop in function body + diff --git a/tests/neg/i6716.check b/tests/neg/i6716.check new file mode 100644 index 000000000000..e70ac4b15f9c --- /dev/null +++ b/tests/neg/i6716.check @@ -0,0 +1,14 @@ +-- Error: tests/neg/i6716.scala:12:39 ---------------------------------------------------------------------------------- +12 | given Monad[Bar] = summon[Monad[Foo]] // error + | ^ + | Result of implicit search for Monad[Foo] will change. + | Current result Bar.given_Monad_Bar will be no longer eligible + | because it is not defined before the search position. + | Result with new rules: Foo.given_Monad_Foo. + | To opt into the new rules, use the `experimental.givenLoopPrevention` language import. + | + | To fix the problem without the language import, you could try one of the following: + | - use a `given ... with` clause as the enclosing given, + | - rearrange definitions so that Bar.given_Monad_Bar comes earlier, + | - use an explicit argument. + | This will be an error in Scala 3.5 and later. diff --git a/tests/neg/i6716.scala b/tests/neg/i6716.scala new file mode 100644 index 000000000000..bbbd9d6d6cd0 --- /dev/null +++ b/tests/neg/i6716.scala @@ -0,0 +1,18 @@ +//> using options -Xfatal-warnings + +trait Monad[T]: + def id: String +class Foo +object Foo { + given Monad[Foo] with { def id = "Foo" } +} + +opaque type Bar = Foo +object Bar { + given Monad[Bar] = summon[Monad[Foo]] // error +} + +object Test extends App { + println(summon[Monad[Foo]].id) + println(summon[Monad[Bar]].id) +} \ No newline at end of file diff --git a/tests/neg/i7294-a.check b/tests/neg/i7294-a.check new file mode 100644 index 000000000000..6fac76a9faa5 --- /dev/null +++ b/tests/neg/i7294-a.check @@ -0,0 +1,25 @@ +-- [E007] Type Mismatch Error: tests/neg/i7294-a.scala:10:20 ----------------------------------------------------------- +10 | case x: T => x.g(10) // error // error + | ^^^^^^^ + | Found: Any + | Required: T + | + | where: T is a type in given instance f with bounds <: foo.Foo + | + | longer explanation available when compiling with `-explain` +-- Error: tests/neg/i7294-a.scala:10:12 -------------------------------------------------------------------------------- +10 | case x: T => x.g(10) // error // error + | ^ + | Result of implicit search for scala.reflect.TypeTest[Nothing, T] will change. + | Current result foo.Test.f will be no longer eligible + | because it is not defined before the search position. + | Result with new rules: No Matching Implicit. + | To opt into the new rules, use the `experimental.givenLoopPrevention` language import. + | + | To fix the problem without the language import, you could try one of the following: + | - use a `given ... with` clause as the enclosing given, + | - rearrange definitions so that foo.Test.f comes earlier, + | - use an explicit argument. + | This will be an error in Scala 3.5 and later. + | + | where: T is a type in given instance f with bounds <: foo.Foo diff --git a/tests/neg/i7294-a.scala b/tests/neg/i7294-a.scala index 13981fa4d375..3453e88cf741 100644 --- a/tests/neg/i7294-a.scala +++ b/tests/neg/i7294-a.scala @@ -1,9 +1,13 @@ +//> using options -Xfatal-warnings + package foo trait Foo { def g(x: Int): Any } -inline given f[T <: Foo]: T = ??? match { - case x: T => x.g(10) // error -} +object Test: + + inline given f[T <: Foo]: T = ??? match { + case x: T => x.g(10) // error // error + } -@main def Test = f + @main def Test = f diff --git a/tests/neg/i7294-b.scala b/tests/neg/i7294-b.scala index 423d5037db96..8c6f9328cc20 100644 --- a/tests/neg/i7294-b.scala +++ b/tests/neg/i7294-b.scala @@ -1,9 +1,11 @@ +//> using options -Xfatal-warnings + package foo trait Foo { def g(x: Any): Any } inline given f[T <: Foo]: T = ??? match { - case x: T => x.g(10) // error + case x: T => x.g(10) // error // error } @main def Test = f diff --git a/tests/neg/looping-givens.scala b/tests/neg/looping-givens.scala new file mode 100644 index 000000000000..357a417f0ed9 --- /dev/null +++ b/tests/neg/looping-givens.scala @@ -0,0 +1,11 @@ +//> using options -Xfatal-warnings + +class A +class B + +given joint(using a: A, b: B): (A & B) = ??? + +def foo(using a: A, b: B) = + given aa: A = summon // error + given bb: B = summon // error + given ab: (A & B) = summon // error diff --git a/tests/pos/i15474.scala b/tests/pos/i15474.scala new file mode 100644 index 000000000000..b006f8b61cf4 --- /dev/null +++ b/tests/pos/i15474.scala @@ -0,0 +1,16 @@ +//> using options -Xfatal-warnings +import scala.language.implicitConversions +import scala.language.experimental.givenLoopPrevention + +object Test2: + given c: Conversion[ String, Int ] = _.toInt // now avoided, was loop not detected, could be used as a fallback to avoid the warning. + +object Prices { + opaque type Price = BigDecimal + + object Price{ + given Ordering[Price] = summon[Ordering[BigDecimal]] // was error, now avoided + } +} + + diff --git a/tests/pos/i6716.scala b/tests/pos/i6716.scala deleted file mode 100644 index 446cd49c9214..000000000000 --- a/tests/pos/i6716.scala +++ /dev/null @@ -1,15 +0,0 @@ -trait Monad[T] -class Foo -object Foo { - given Monad[Foo] with {} -} - -opaque type Bar = Foo -object Bar { - given Monad[Bar] = summon[Monad[Foo]] -} - -object Test { - val mf = summon[Monad[Foo]] - val mb = summon[Monad[Bar]] -} \ No newline at end of file diff --git a/tests/pos/looping-givens.scala b/tests/pos/looping-givens.scala new file mode 100644 index 000000000000..1b620b5c113e --- /dev/null +++ b/tests/pos/looping-givens.scala @@ -0,0 +1,11 @@ +import language.experimental.givenLoopPrevention + +class A +class B + +given joint(using a: A, b: B): (A & B) = ??? + +def foo(using a: A, b: B) = + given aa: A = summon // error + given bb: B = summon // error + given ab: (A & B) = summon // error diff --git a/tests/run/i17115.check b/tests/run/i17115.check new file mode 100644 index 000000000000..61c83cba41ce --- /dev/null +++ b/tests/run/i17115.check @@ -0,0 +1,2 @@ +4 +5 diff --git a/tests/pos/i17115.scala b/tests/run/i17115.scala similarity index 100% rename from tests/pos/i17115.scala rename to tests/run/i17115.scala diff --git a/tests/run/i6716.check b/tests/run/i6716.check new file mode 100644 index 000000000000..bb85bd267288 --- /dev/null +++ b/tests/run/i6716.check @@ -0,0 +1,2 @@ +Foo +Foo diff --git a/tests/run/i6716.scala b/tests/run/i6716.scala new file mode 100644 index 000000000000..4cca37f96a6f --- /dev/null +++ b/tests/run/i6716.scala @@ -0,0 +1,20 @@ +//> using options -Xfatal-warnings + +import scala.language.experimental.givenLoopPrevention + +trait Monad[T]: + def id: String +class Foo +object Foo { + given Monad[Foo] with { def id = "Foo" } +} + +opaque type Bar = Foo +object Bar { + given Monad[Bar] = summon[Monad[Foo]] // was error, fixed by givenLoopPrevention +} + +object Test extends App { + println(summon[Monad[Foo]].id) + println(summon[Monad[Bar]].id) +} \ No newline at end of file