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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 #10864 Fixes #11738
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+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
@@ -1740,6 +1740,27 @@ object Parsers {
17401740
/** The block in a quote or splice */
17411741
def stagedBlock() = inBraces(block(simplify = true))
17421742

1743+
/** TypeBlock ::= {TypeBlockStat semi} Type
1744+
*/
1745+
def typeBlock(): Tree =
1746+
typeBlockStats() match
1747+
case Nil => typ()
1748+
case tdefs => Block(tdefs, typ())
1749+
1750+
def typeBlockStats(): List[Tree] =
1751+
val tdefs = new ListBuffer[Tree]
1752+
while in.token == TYPE do tdefs += typeBlockStat()
1753+
tdefs.toList
1754+
1755+
/** TypeBlockStat ::= ‘type’ {nl} TypeDcl
1756+
*/
1757+
def typeBlockStat(): Tree =
1758+
val mods = defAnnotsMods(BitSet())
1759+
val tdef = typeDefOrDcl(in.offset, in.skipToken(mods))
1760+
if in.token == SEMI then in.nextToken()
1761+
if in.isNewLine then in.nextToken()
1762+
tdef
1763+
17431764
/** ExprSplice ::= ‘$’ spliceId -- if inside quoted block
17441765
* | ‘$’ ‘{’ Block ‘}’ -- unless inside quoted pattern
17451766
* | ‘$’ ‘{’ Pattern ‘}’ -- when inside quoted pattern
@@ -2478,7 +2499,7 @@ object Parsers {
24782499
atSpan(in.skipToken()) {
24792500
withinStaged(StageKind.Quoted | (if (location.inPattern) StageKind.QuotedPattern else 0)) {
24802501
val body =
2481-
if (in.token == LBRACKET) inBrackets(typ())
2502+
if (in.token == LBRACKET) inBrackets(typeBlock())
24822503
else stagedBlock()
24832504
Quote(body, Nil)
24842505
}
@@ -3745,6 +3766,8 @@ object Parsers {
37453766
else makeTypeDef(bounds)
37463767
case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
37473768
makeTypeDef(typeBounds())
3769+
case _ if (staged & StageKind.QuotedPattern) != 0 =>
3770+
makeTypeDef(typeBounds())
37483771
case _ =>
37493772
syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
37503773
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
@@ -212,11 +212,11 @@ trait QuotesAndSplices {
212212
* )
213213
* ```
214214
*/
215-
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Bind], Tree, List[Tree]) = {
215+
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Tree], Tree, List[Tree]) = {
216216
val ctx0 = ctx
217217

218-
val typeBindings: collection.mutable.Map[Symbol, Bind] = collection.mutable.Map.empty
219-
def getBinding(sym: Symbol): Bind =
218+
val typeBindings: collection.mutable.Map[Symbol, Tree] = collection.mutable.Map.empty
219+
def getBinding(sym: Symbol): Tree =
220220
typeBindings.getOrElseUpdate(sym, {
221221
val bindingBounds = sym.info
222222
val bsym = newPatternBoundSymbol(sym.name.toString.stripPrefix("$").toTypeName, bindingBounds, quoted.span)
@@ -407,6 +407,17 @@ trait QuotesAndSplices {
407407
}
408408
val (untpdTypeVariables, quoted0) = desugar.quotedPatternTypeVariables(desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt))))
409409

410+
for untpdTypeVariable <- untpdTypeVariables do untpdTypeVariable.rhs match
411+
case _: TypeBoundsTree => // ok
412+
case LambdaTypeTree(_, body: TypeBoundsTree) => // ok
413+
case _ => report.error("Quote type variable definition cannot be an alias", untpdTypeVariable.srcPos)
414+
415+
if quoted.isType && untpdTypeVariables.nonEmpty then
416+
checkExperimentalFeature(
417+
"explicit type variable declarations quoted type patterns (SIP-53)",
418+
untpdTypeVariables.head.srcPos,
419+
"\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
420+
410421
val (typeTypeVariables, patternCtx) =
411422
val quoteCtx = quotePatternContext()
412423
if untpdTypeVariables.isEmpty then (Nil, quoteCtx)
@@ -417,7 +428,7 @@ trait QuotesAndSplices {
417428
addQuotedPatternTypeVariable(typeVariable.symbol)
418429

419430
val pattern =
420-
if quoted.isType then typedType(quoted0, WildcardType)
431+
if quoted.isType then typedType(quoted0, WildcardType)(using patternCtx)
421432
else typedExpr(quoted0, WildcardType)
422433

423434
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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