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135 changes: 135 additions & 0 deletions
135
compiler/src/dotty/tools/dotc/transform/ElimByNameParams.scala
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,135 @@ | ||
| package dotty.tools | ||
| package dotc | ||
| package transform | ||
|
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| import core._ | ||
| import Contexts._ | ||
| import Symbols._ | ||
| import Types._ | ||
| import Flags._ | ||
| import SymDenotations.* | ||
| import DenotTransformers.InfoTransformer | ||
| import NameKinds.SuperArgName | ||
| import core.StdNames.nme | ||
| import MegaPhase.* | ||
| import Decorators.* | ||
| import reporting.trace | ||
|
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| /** This phase translates arguments to call-by-name parameters, using the rules | ||
| * | ||
| * x ==> x if x is a => parameter | ||
| * e.apply() ==> <cbn-arg>(e) if e is pure | ||
| * e ==> <cbn-arg>(() => e) for all other arguments | ||
| * | ||
| * where | ||
| * | ||
| * <cbn-arg>: [T](() => T): T | ||
| * | ||
| * is a synthetic method defined in Definitions. Erasure will later strip the <cbn-arg> wrappers. | ||
| */ | ||
| class ElimByNameParams extends MiniPhase, InfoTransformer: | ||
| thisPhase => | ||
|
|
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| import ast.tpd._ | ||
|
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| override def phaseName: String = ElimByNameParams.name | ||
|
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| override def runsAfterGroupsOf: Set[String] = Set(ExpandSAMs.name, ElimRepeated.name) | ||
| // - ExpanSAMs applied to partial functions creates methods that need | ||
| // to be fully defined before converting. Test case is pos/i9391.scala. | ||
| // - ByNameLambda needs to run in a group after ElimRepeated since ElimRepeated | ||
| // works on simple arguments but not converted closures, and it sees the arguments | ||
| // after transformations by subsequent miniphases in the same group. | ||
|
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| override def changesParents: Boolean = true | ||
| // Expr types in parent type arguments are changed to function types. | ||
|
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| /** If denotation had an ExprType before, it now gets a function type */ | ||
| private def exprBecomesFunction(symd: SymDenotation)(using Context): Boolean = | ||
| symd.is(Param) || symd.is(ParamAccessor, butNot = Method) | ||
|
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| def transformInfo(tp: Type, sym: Symbol)(using Context): Type = tp match { | ||
| case ExprType(rt) if exprBecomesFunction(sym) => | ||
| defn.ByNameFunction(rt) | ||
| case tp: MethodType => | ||
| def exprToFun(tp: Type) = tp match | ||
| case ExprType(rt) => defn.ByNameFunction(rt) | ||
| case tp => tp | ||
| tp.derivedLambdaType( | ||
| paramInfos = tp.paramInfos.mapConserve(exprToFun), | ||
| resType = transformInfo(tp.resType, sym)) | ||
| case tp: PolyType => | ||
| tp.derivedLambdaType(resType = transformInfo(tp.resType, sym)) | ||
| case _ => tp | ||
| } | ||
|
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| override def infoMayChange(sym: Symbol)(using Context): Boolean = | ||
| sym.is(Method) || exprBecomesFunction(sym) | ||
|
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| def byNameClosure(arg: Tree, argType: Type)(using Context): Tree = | ||
| val meth = newAnonFun(ctx.owner, MethodType(Nil, argType), coord = arg.span) | ||
| Closure(meth, | ||
| _ => arg.changeOwnerAfter(ctx.owner, meth, thisPhase), | ||
| targetType = defn.ByNameFunction(argType) | ||
| ).withSpan(arg.span) | ||
|
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| private def isByNameRef(tree: Tree)(using Context): Boolean = | ||
| defn.isByNameFunction(tree.tpe.widen) | ||
|
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| /** Map `tree` to `tree.apply()` is `tree` is of type `() ?=> T` */ | ||
| private def applyIfFunction(tree: Tree)(using Context) = | ||
| if isByNameRef(tree) then | ||
| val tree0 = transformFollowing(tree) | ||
| atPhase(next) { tree0.select(defn.ContextFunction0_apply).appliedToNone } | ||
| else tree | ||
|
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| override def transformIdent(tree: Ident)(using Context): Tree = | ||
| applyIfFunction(tree) | ||
|
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| override def transformSelect(tree: Select)(using Context): Tree = | ||
| applyIfFunction(tree) | ||
|
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| override def transformTypeApply(tree: TypeApply)(using Context): Tree = tree match { | ||
| case TypeApply(Select(_, nme.asInstanceOf_), arg :: Nil) => | ||
| // tree might be of form e.asInstanceOf[x.type] where x becomes a function. | ||
| // See pos/t296.scala | ||
| applyIfFunction(tree) | ||
| case _ => tree | ||
| } | ||
|
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| override def transformApply(tree: Apply)(using Context): Tree = | ||
| trace(s"transforming ${tree.show} at phase ${ctx.phase}", show = true) { | ||
|
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| def transformArg(arg: Tree, formal: Type): Tree = formal match | ||
| case defn.ByNameFunction(formalResult) => | ||
| def stripTyped(t: Tree): Tree = t match | ||
| case Typed(expr, _) => stripTyped(expr) | ||
| case _ => t | ||
| stripTyped(arg) match | ||
| case Apply(Select(qual, nme.apply), Nil) | ||
| if isByNameRef(qual) && (isPureExpr(qual) || qual.symbol.isAllOf(InlineParam)) => | ||
| qual | ||
| case _ => | ||
| if isByNameRef(arg) || arg.symbol.name.is(SuperArgName) | ||
| then arg | ||
| else | ||
| var argType = arg.tpe.widenIfUnstable | ||
| if argType.isBottomType then argType = formalResult | ||
| byNameClosure(arg, argType) | ||
| case _ => | ||
| arg | ||
|
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| val mt @ MethodType(_) = tree.fun.tpe.widen | ||
| val args1 = tree.args.zipWithConserve(mt.paramInfos)(transformArg) | ||
| cpy.Apply(tree)(tree.fun, args1) | ||
| } | ||
|
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| override def transformValDef(tree: ValDef)(using Context): Tree = | ||
| atPhase(next) { | ||
| if exprBecomesFunction(tree.symbol) then | ||
| cpy.ValDef(tree)(tpt = tree.tpt.withType(tree.symbol.info)) | ||
| else tree | ||
| } | ||
|
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| object ElimByNameParams: | ||
| val name: String = "elimByNameParams" |