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Revised given syntax (scala#21208)
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Update given syntax to latest discussed variant in the SIP

tests/pos/given-syntax.scala shows a semi-systematic list of possible
syntax forms.
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@odersky
odersky authored Jul 25, 2024
2 parents 9e4aea4 + 62c71c0 commit 3dfd762
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Showing 19 changed files with 680 additions and 145 deletions.
160 changes: 112 additions & 48 deletions compiler/src/dotty/tools/dotc/parsing/Parsers.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -972,18 +972,16 @@ object Parsers {
followedByToken(LARROW) // `<-` comes before possible statement starts
}

/** Are the next token the "GivenSig" part of a given definition,
* i.e. an identifier followed by type and value parameters, followed by `:`?
/** Are the next tokens a valid continuation of a named given def?
* i.e. an identifier, possibly followed by type and value parameters, followed by `:`?
* @pre The current token is an identifier
*/
def followingIsOldStyleGivenSig() =
def followingIsGivenDefWithColon() =
val lookahead = in.LookaheadScanner()
if lookahead.isIdent then
lookahead.nextToken()
var paramsSeen = false
def skipParams(): Unit =
if lookahead.token == LPAREN || lookahead.token == LBRACKET then
paramsSeen = true
lookahead.skipParens()
skipParams()
else if lookahead.isNewLine then
Expand All @@ -1002,6 +1000,11 @@ object Parsers {
}
}

def followingIsArrow() =
val lookahead = in.LookaheadScanner()
lookahead.skipParens()
lookahead.token == ARROW

def followingIsExtension() =
val next = in.lookahead.token
next == LBRACKET || next == LPAREN
Expand Down Expand Up @@ -3441,7 +3444,11 @@ object Parsers {
/** ContextTypes ::= FunArgType {‘,’ FunArgType}
*/
def contextTypes(paramOwner: ParamOwner, numLeadParams: Int, impliedMods: Modifiers): List[ValDef] =
val tps = commaSeparated(() => paramTypeOf(() => toplevelTyp()))
typesToParams(
commaSeparated(() => paramTypeOf(() => toplevelTyp())),
paramOwner, numLeadParams, impliedMods)

def typesToParams(tps: List[Tree], paramOwner: ParamOwner, numLeadParams: Int, impliedMods: Modifiers): List[ValDef] =
var counter = numLeadParams
def nextIdx = { counter += 1; counter }
val paramFlags = if paramOwner.isClass then LocalParamAccessor else Param
Expand All @@ -3468,18 +3475,20 @@ object Parsers {
def termParamClause(
paramOwner: ParamOwner,
numLeadParams: Int, // number of parameters preceding this clause
firstClause: Boolean = false // clause is the first in regular list of clauses
firstClause: Boolean = false, // clause is the first in regular list of clauses
initialMods: Modifiers = EmptyModifiers
): List[ValDef] = {
var impliedMods: Modifiers = EmptyModifiers
var impliedMods: Modifiers = initialMods

def addParamMod(mod: () => Mod) = impliedMods = addMod(impliedMods, atSpan(in.skipToken()) { mod() })

def paramMods() =
if in.token == IMPLICIT then
addParamMod(() => Mod.Implicit())
else
if isIdent(nme.using) then
addParamMod(() => Mod.Given())
else if isIdent(nme.using) then
if initialMods.is(Given) then
syntaxError(em"`using` is already implied here, should not be given explicitly", in.offset)
addParamMod(() => Mod.Given())

def param(): ValDef = {
val start = in.offset
Expand Down Expand Up @@ -4144,18 +4153,67 @@ object Parsers {
* OldGivenSig ::= [id] [DefTypeParamClause] {UsingParamClauses} ‘:’
* StructuralInstance ::= ConstrApp {‘with’ ConstrApp} [‘with’ WithTemplateBody]
*
* NewGivenDef ::= [GivenConditional '=>'] NewGivenSig
* GivenConditional ::= [DefTypeParamClause | UsingParamClause] {UsingParamClause}
* NewGivenSig ::= GivenType ['as' id] ([‘=’ Expr] | TemplateBody)
* | ConstrApps ['as' id] TemplateBody
*
* NewGivenDef ::= [id ':'] GivenSig
* GivenSig ::= GivenImpl
* | '(' ')' '=>' GivenImpl
* | GivenConditional '=>' GivenSig
* GivenImpl ::= GivenType ([‘=’ Expr] | TemplateBody)
* | ConstrApps TemplateBody
* GivenConditional ::= DefTypeParamClause
* | DefTermParamClause
* | '(' FunArgTypes ')'
* | GivenType
* GivenType ::= AnnotType1 {id [nl] AnnotType1}
*/
def givenDef(start: Offset, mods: Modifiers, givenMod: Mod) = atSpan(start, nameStart) {
var mods1 = addMod(mods, givenMod)
val nameStart = in.offset
var name = if isIdent && followingIsOldStyleGivenSig() then ident() else EmptyTermName
var newSyntaxAllowed = in.featureEnabled(Feature.modularity)
val hasEmbeddedColon = !in.isColon && followingIsGivenDefWithColon()
val name = if isIdent && hasEmbeddedColon then ident() else EmptyTermName

def implemented(): List[Tree] =
if isSimpleLiteral then
rejectWildcardType(annotType()) :: Nil
else constrApp() match
case parent: Apply => parent :: moreConstrApps()
case parent if in.isIdent && newSyntaxAllowed =>
infixTypeRest(parent, _ => annotType1()) :: Nil
case parent => parent :: moreConstrApps()

// The term parameters and parent references */
def newTermParamssAndParents(numLeadParams: Int): (List[List[ValDef]], List[Tree]) =
if in.token == LPAREN && followingIsArrow() then
val params =
if in.lookahead.token == RPAREN && numLeadParams == 0 then
in.nextToken()
in.nextToken()
Nil
else
termParamClause(
ParamOwner.Given, numLeadParams, firstClause = true, initialMods = Modifiers(Given))
accept(ARROW)
if params.isEmpty then (params :: Nil, implemented())
else
val (paramss, parents) = newTermParamssAndParents(numLeadParams + params.length)
(params :: paramss, parents)
else
val parents = implemented()
if in.token == ARROW && parents.length == 1 && parents.head.isType then
in.nextToken()
val (paramss, parents1) = newTermParamssAndParents(numLeadParams + parents.length)
(typesToParams(parents, ParamOwner.Given, numLeadParams, Modifiers(Given)) :: paramss, parents1)
else
(Nil, parents)

/** Type parameters, term parameters and parent clauses */
def newSignature(): (List[TypeDef], (List[List[ValDef]], List[Tree])) =
val tparams =
if in.token == LBRACKET then
try typeParamClause(ParamOwner.Given)
finally accept(ARROW)
else Nil
(tparams, newTermParamssAndParents(numLeadParams = 0))

def moreConstrApps() =
if newSyntaxAllowed && in.token == COMMA then
Expand All @@ -4176,47 +4234,49 @@ object Parsers {
.asInstanceOf[List[ParamClause]]

val gdef =
val tparams = typeParamClauseOpt(ParamOwner.Given)
newLineOpt()
val vparamss =
if in.token == LPAREN && (in.lookahead.isIdent(nme.using) || name != EmptyTermName)
then termParamClauses(ParamOwner.Given)
else Nil
newLinesOpt()
val noParams = tparams.isEmpty && vparamss.isEmpty
val hasParamsOrId = !name.isEmpty || !noParams
if hasParamsOrId then
if in.isColon then
newSyntaxAllowed = false
val (tparams, (vparamss0, parents)) =
if in.isColon && !name.isEmpty then
in.nextToken()
else if newSyntaxAllowed then accept(ARROW)
else acceptColon()
val parents =
if isSimpleLiteral then
rejectWildcardType(annotType()) :: Nil
else constrApp() match
case parent: Apply => parent :: moreConstrApps()
case parent if in.isIdent && newSyntaxAllowed =>
infixTypeRest(parent, _ => annotType1()) :: Nil
case parent => parent :: moreConstrApps()
if newSyntaxAllowed && in.isIdent(nme.as) then
in.nextToken()
name = ident()

newSignature()
else if hasEmbeddedColon then
newSyntaxAllowed = false
val tparamsOld = typeParamClauseOpt(ParamOwner.Given)
newLineOpt()
val vparamssOld =
if in.token == LPAREN && (in.lookahead.isIdent(nme.using) || name != EmptyTermName)
then termParamClauses(ParamOwner.Given)
else Nil
acceptColon()
(tparamsOld, (vparamssOld, implemented()))
else
newSignature()
val hasParams = tparams.nonEmpty || vparamss0.nonEmpty
val vparamss = vparamss0 match
case Nil :: Nil => Nil
case _ => vparamss0
val parentsIsType = parents.length == 1 && parents.head.isType
if in.token == EQUALS && parentsIsType then
// given alias
accept(EQUALS)
mods1 |= Final
if noParams && !mods.is(Inline) then
if !hasParams && !mods.is(Inline) then
mods1 |= Lazy
ValDef(name, parents.head, subExpr())
else
DefDef(name, adjustDefParams(joinParams(tparams, vparamss)), parents.head, subExpr())
else if (isStatSep || isStatSeqEnd) && parentsIsType && !newSyntaxAllowed then
else if (isStatSep || isStatSeqEnd) && parentsIsType
&& !(name.isEmpty && newSyntaxAllowed)
// under new syntax, anonymous givens are translated to concrete classes,
// so it's treated as a structural instance.
then
// old-style abstract given
if name.isEmpty then
syntaxError(em"anonymous given cannot be abstract")
syntaxError(em"Anonymous given cannot be abstract, or maybe you want to define a concrete given and are missing a `()` argument?", in.lastOffset)
if newSyntaxAllowed then
warning(
em"""This defines an abstract given, which is deprecated. Use a `deferred` given instead.
|Or, if you intend to define a concrete given, follow the type with `()` arguments.""",
in.lastOffset)
DefDef(name, adjustDefParams(joinParams(tparams, vparamss)), parents.head, EmptyTree)
else
// structural instance
Expand All @@ -4228,12 +4288,16 @@ object Parsers {
val templ =
if isStatSep || isStatSeqEnd then
Template(constr, parents, Nil, EmptyValDef, Nil)
else if !newSyntaxAllowed || in.token == WITH then
else if !newSyntaxAllowed
|| in.token == WITH && tparams.isEmpty && vparamss.isEmpty
// if new syntax is still allowed and there are parameters, they mist be new style conditions,
// so old with-style syntax would not be allowed.
then
withTemplate(constr, parents)
else
possibleTemplateStart()
templateBodyOpt(constr, parents, Nil)
if noParams && !mods.is(Inline) then ModuleDef(name, templ)
if !hasParams && !mods.is(Inline) then ModuleDef(name, templ)
else TypeDef(name.toTypeName, templ)
end gdef
finalizeDef(gdef, mods1, start)
Expand Down
14 changes: 10 additions & 4 deletions docs/_docs/internals/syntax.md
View file
Original file line number Diff line number Diff line change
Expand Up @@ -471,10 +471,16 @@ ConstrMods ::= {Annotation} [AccessModifier]
ObjectDef ::= id [Template] ModuleDef(mods, name, template) // no constructor
EnumDef ::= id ClassConstr InheritClauses EnumBody
GivenDef ::= [GivenConditional '=>'] GivenSig
GivenConditional ::= [DefTypeParamClause | UsingParamClause] {UsingParamClause}
GivenSig ::= GivenType ['as' id] ([‘=’ Expr] | TemplateBody)
| ConstrApps ['as' id] TemplateBody
GivenDef ::= [id ':'] GivenSig
GivenSig ::= GivenImpl
| '(' ')' '=>' GivenImpl
| GivenConditional '=>' GivenSig
GivenImpl ::= GivenType ([‘=’ Expr] | TemplateBody)
| ConstrApps TemplateBody
GivenConditional ::= DefTypeParamClause
| DefTermParamClause
| '(' FunArgTypes ')'
| GivenType
GivenType ::= AnnotType1 {id [nl] AnnotType1}
Extension ::= ‘extension’ [DefTypeParamClause] {UsingParamClause}
Expand Down
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