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Support type variable definitions in quoted patterns
Support explicit type variable definition in quoted patterns. This allows users to set explicit bounds or use the binding twice. Previously this was only possible on quoted expression patterns case '{ ... }. ```scala case '[type x; x] => case '[type x; Map[x, x]] => case '[type x <: List[Any]; x] => case '[type f[X]; f] => case '[type f <: AnyKind; f] => ``` Fixes scala#10864 Fixes scala#11738
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13 files changed

+202
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‎compiler/src/dotty/tools/dotc/parsing/Parsers.scala

Lines changed: 24 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1735,6 +1735,27 @@ object Parsers {
17351735
/** The block in a quote or splice */
17361736
def stagedBlock() = inBraces(block(simplify = true))
17371737

1738+
/** TypeBlock ::= {TypeBlockStat semi} Type
1739+
*/
1740+
def typeBlock(): Tree =
1741+
typeBlockStats() match
1742+
case Nil => typ()
1743+
case tdefs => Block(tdefs, typ())
1744+
1745+
def typeBlockStats(): List[Tree] =
1746+
val tdefs = new ListBuffer[Tree]
1747+
while in.token == TYPE do tdefs += typeBlockStat()
1748+
tdefs.toList
1749+
1750+
/** TypeBlockStat ::= ‘type’ {nl} TypeDcl
1751+
*/
1752+
def typeBlockStat(): Tree =
1753+
val mods = defAnnotsMods(BitSet())
1754+
val tdef = typeDefOrDcl(in.offset, in.skipToken(mods))
1755+
if in.token == SEMI then in.nextToken()
1756+
if in.isNewLine then in.nextToken()
1757+
tdef
1758+
17381759
/** ExprSplice ::= ‘$’ spliceId -- if inside quoted block
17391760
* | ‘$’ ‘{’ Block ‘}’ -- unless inside quoted pattern
17401761
* | ‘$’ ‘{’ Pattern ‘}’ -- when inside quoted pattern
@@ -2498,7 +2519,7 @@ object Parsers {
24982519
atSpan(in.skipToken()) {
24992520
withinStaged(StageKind.Quoted | (if (location.inPattern) StageKind.QuotedPattern else 0)) {
25002521
val body =
2501-
if (in.token == LBRACKET) inBrackets(typ())
2522+
if (in.token == LBRACKET) inBrackets(typeBlock())
25022523
else stagedBlock()
25032524
Quote(body)
25042525
}
@@ -3764,6 +3785,8 @@ object Parsers {
37643785
else makeTypeDef(bounds)
37653786
case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
37663787
makeTypeDef(typeBounds())
3788+
case _ if (staged & StageKind.QuotedPattern) != 0 =>
3789+
makeTypeDef(typeBounds())
37673790
case _ =>
37683791
syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
37693792
return EmptyTree // return to avoid setting the span to EmptyTree

‎compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

Lines changed: 15 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -214,11 +214,11 @@ trait QuotesAndSplices {
214214
* )
215215
* ```
216216
*/
217-
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Bind], Tree, List[Tree]) = {
217+
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Tree], Tree, List[Tree]) = {
218218
val ctx0 = ctx
219219

220-
val typeBindings: collection.mutable.Map[Symbol, Bind] = collection.mutable.Map.empty
221-
def getBinding(sym: Symbol): Bind =
220+
val typeBindings: collection.mutable.Map[Symbol, Tree] = collection.mutable.Map.empty
221+
def getBinding(sym: Symbol): Tree =
222222
typeBindings.getOrElseUpdate(sym, {
223223
val bindingBounds = sym.info
224224
val bsym = newPatternBoundSymbol(sym.name.toString.stripPrefix("$").toTypeName, bindingBounds, quoted.span)
@@ -396,6 +396,17 @@ trait QuotesAndSplices {
396396
}
397397
val (untpdTypeVariables, quoted0) = desugar.quotedPatternTypeVariables(desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt))))
398398

399+
for untpdTypeVariable <- untpdTypeVariables do untpdTypeVariable.rhs match
400+
case _: TypeBoundsTree => // ok
401+
case LambdaTypeTree(_, body: TypeBoundsTree) => // ok
402+
case _ => report.error("Quote type variable definition cannot be an alias", untpdTypeVariable.srcPos)
403+
404+
if quoted.isType && untpdTypeVariables.nonEmpty then
405+
checkExperimentalFeature(
406+
"explicit type variable declarations quoted type patterns (SIP-53)",
407+
untpdTypeVariables.head.srcPos,
408+
"\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
409+
399410
val (typeTypeVariables, patternCtx) =
400411
val quoteCtx = quotePatternContext()
401412
if untpdTypeVariables.isEmpty then (Nil, quoteCtx)
@@ -406,7 +417,7 @@ trait QuotesAndSplices {
406417
addQuotedPatternTypeVariable(typeVariable.symbol)
407418

408419
val pattern =
409-
if quoted.isType then typedType(quoted0, WildcardType)
420+
if quoted.isType then typedType(quoted0, WildcardType)(using patternCtx)
410421
else typedExpr(quoted0, WildcardType)
411422

412423
if untpdTypeVariables.isEmpty then pattern

‎docs/_docs/reference/metaprogramming/macros.md

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -530,15 +530,24 @@ It works the same way as a quoted pattern but is restricted to contain a type.
530530
Type variables can be used in quoted type patterns to extract a type.
531531

532532
```scala
533-
def empty[T: Type]: Expr[T] =
533+
def empty[T: Type](using Quotes): Expr[T] =
534534
Type.of[T] match
535535
case '[String] => '{ "" }
536536
case '[List[t]] => '{ List.empty[t] }
537+
case '[type t <: Option[Int]; List[t]] => '{ List.empty[t] }
537538
...
538539
```
539-
540540
`Type.of[T]` is used to summon the given instance of `Type[T]` in scope, it is equivalent to `summon[Type[T]]`.
541541

542+
It is possible to match against a higer-kinded type using appropriate type bounds on type variables.
543+
```scala
544+
def empty[K <: AnyKind : Type](using Quotes): Type[?] =
545+
Type.of[K] match
546+
case '[type f[X]; f] => Type.of[f]
547+
case '[type f[X <: Int, Y]; f] => Type.of[f]
548+
case '[type k <: AnyKind; k ] => Type.of[k]
549+
```
550+
542551
#### Type testing and casting
543552
It is important to note that instance checks and casts on `Expr`, such as `isInstanceOf[Expr[T]]` and `asInstanceOf[Expr[T]]`, will only check if the instance is of the class `Expr` but will not be able to check the `T` argument.
544553
These cases will issue a warning at compile-time, but if they are ignored, they can result in unexpected behavior.

‎docs/_docs/reference/syntax.md

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -274,7 +274,7 @@ ColonArgument ::= colon [LambdaStart]
274274
LambdaStart ::= FunParams (‘=>’ | ‘?=>’)
275275
| HkTypeParamClause ‘=>’
276276
Quoted ::= ‘'’ ‘{’ Block ‘}’
277-
| ‘'’ ‘[’ Type ‘]’
277+
| ‘'’ ‘[’ TypeBlock ‘]’
278278
ExprSplice ::= spliceId -- if inside quoted block
279279
| ‘$’ ‘{’ Block ‘}’ -- unless inside quoted pattern
280280
| ‘$’ ‘{’ Pattern ‘}’ -- when inside quoted pattern
@@ -293,6 +293,8 @@ BlockStat ::= Import
293293
| Extension
294294
| Expr1
295295
| EndMarker
296+
TypeBlock ::= {TypeBlockStat semi} Type
297+
TypeBlockStat ::= ‘type’ {nl} TypeDcl
296298
297299
ForExpr ::= ‘for’ ‘(’ Enumerators0 ‘)’ {nl} [‘do‘ | ‘yield’] Expr
298300
| ‘for’ ‘{’ Enumerators0 ‘}’ {nl} [‘do‘ | ‘yield’] Expr

‎tests/neg-custom-args/no-experimental/sip-53-exprimental-b.scala

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
import scala.quoted.*
2+
3+
def empty[K <: AnyKind : Type](using Quotes): Type[?] =
4+
Type.of[K] match
5+
case '[type t; `t`] => Type.of[t] // error
6+
case '[type f[X]; `f`] => Type.of[f] // error
7+
case '[type f[X <: Int, Y]; `f`] => Type.of[f] // error
8+
case '[type k <: AnyKind; `k` ] => Type.of[k] // error

‎tests/neg-macros/quote-pattern-type-var-bounds.scala

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,22 @@
1+
import scala.quoted.*
2+
def types(t: Type[?])(using Quotes) = t match {
3+
case '[ type t; Int ] =>
4+
case '[ type t <: Int; Int ] =>
5+
case '[ type t >: 1 <: Int; Int ] =>
6+
case '[ type t = Int; Int ] => // error
7+
case '[ type t = scala.Int; Int ] => // error
8+
case '[ type f[t] <: List[Any]; Int ] =>
9+
case '[ type f[t <: Int] <: List[Any]; Int ] =>
10+
case '[ type f[t] = List[Any]; Int ] => // error
11+
}
12+
13+
def expressions(x: Expr[Any])(using Quotes) = x match {
14+
case '{ type t; () } =>
15+
case '{ type t <: Int; () } =>
16+
case '{ type t >: 1 <: Int; () } =>
17+
case '{ type t = Int; () } => // error
18+
case '{ type t = scala.Int; () } => // error
19+
case '{ type f[t] <: List[Any]; () } =>
20+
case '{ type f[t <: Int] <: List[Any]; () } =>
21+
case '{ type f[t] = List[Any]; () } => // error
22+
}

‎tests/pos-macros/i10864/Macro_1.scala

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
1+
import scala.quoted._
2+
3+
case class T(t: Type[_])
4+
5+
object T {
6+
def impl[T <: AnyKind](using tt: Type[T])(using Quotes): Expr[Unit] = {
7+
val t = T(tt)
8+
t.t match
9+
case '[type x <: AnyKind; x] => // ok
10+
case _ => quotes.reflect.report.error("not ok :(")
11+
'{}
12+
}
13+
14+
inline def run[T <: AnyKind] = ${ impl[T] }
15+
}

‎tests/pos-macros/i10864/Test_2.scala

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,4 @@
1+
def test =
2+
T.run[List]
3+
T.run[Map]
4+
T.run[Tuple22]

‎tests/pos-macros/i10864a/Macro_1.scala

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
import scala.quoted._
2+
3+
case class T(t: Type[_])
4+
5+
object T {
6+
def impl[T <: AnyKind](using tt: Type[T])(using Quotes): Expr[Unit] = {
7+
val t = T(tt)
8+
t.t match
9+
case '[type x; x] =>
10+
assert(Type.show[x] == "scala.Int", Type.show[x])
11+
case '[type f[X]; f] =>
12+
assert(Type.show[f] == "[A >: scala.Nothing <: scala.Any] => scala.collection.immutable.List[A]", Type.show[f])
13+
case '[type f[X <: Int]; f] =>
14+
assert(Type.show[f] == "[T >: scala.Nothing <: scala.Int] => C[T]", Type.show[f])
15+
case '[type f <: AnyKind; f] =>
16+
assert(Type.show[f] == "[K >: scala.Nothing <: scala.Any, V >: scala.Nothing <: scala.Any] => scala.collection.immutable.Map[K, V]", Type.show[f])
17+
'{}
18+
}
19+
20+
inline def run[T <: AnyKind] = ${ impl[T] }
21+
}

‎tests/pos-macros/i10864a/Test_2.scala

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
@main
2+
def run =
3+
T.run[Int]
4+
T.run[C]
5+
T.run[List]
6+
T.run[Map]
7+
8+
class C[T <: Int]

‎tests/pos-macros/i11738.scala

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
import scala.quoted.*
2+
3+
def blah[A](using Quotes, Type[A]): Expr[Unit] =
4+
Type.of[A] match
5+
case '[h *: t] => println(s"h = ${Type.show[h]}, t = ${Type.show[t]}") // ok
6+
case '[type f[X]; f[a]] => println(s"f = ${Type.show[f]}, a = ${Type.show[a]}") // error
7+
case _ =>
8+
'{()}

‎tests/pos-macros/i7264.scala

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3,5 +3,6 @@ class Foo {
33
def f[T2](t: Type[T2])(using Quotes) = t match {
44
case '[ *:[Int, t2] ] =>
55
Type.of[ *:[Int, t2] ]
6+
case '[ type t <: Tuple; *:[t, t] ] =>
67
}
78
}

‎tests/pos-macros/multiline-quote-patterns.scala

Lines changed: 62 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,62 @@
1+
import scala.quoted.*
2+
def types(t: Type[?])(using Quotes) = t match {
3+
case '[
4+
type t;
5+
t
6+
] =>
7+
8+
case '[
9+
type t
10+
t
11+
] =>
12+
13+
case '[
14+
type t
15+
List[t]
16+
] =>
17+
18+
case '[
19+
type t;
20+
type u;
21+
Map[t, u]
22+
] =>
23+
24+
case '[
25+
type t
26+
type u
27+
Map[t, u]
28+
] =>
29+
30+
case '[
31+
type t; type u
32+
t => u
33+
] =>
34+
}
35+
36+
def expressions(x: Expr[Any])(using Quotes) = x match {
37+
case '{
38+
type t;
39+
$x: t
40+
} =>
41+
42+
case '{
43+
type t
44+
$x: t
45+
} =>
46+
47+
case '{
48+
type t;
49+
List()
50+
} =>
51+
52+
case '{
53+
type t
54+
List()
55+
} =>
56+
57+
case '{
58+
type t
59+
type u
60+
Map.empty[t, u]
61+
} =>
62+
}

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