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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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+171
-8
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12 files changed

+171
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‎compiler/src/dotty/tools/dotc/parsing/Parsers.scala

Lines changed: 20 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1735,6 +1735,23 @@ object Parsers {
17351735
/** The block in a quote or splice */
17361736
def stagedBlock() = inBraces(block(simplify = true))
17371737

1738+
/** TypeBlock ::= {TypeBlockStat semi} Type
1739+
* TypeBlockStat ::= ‘type’ {nl} TypeDcl
1740+
*/
1741+
def typeBlock(): Tree =
1742+
quotePatternTypeVars() match
1743+
case Nil => typ()
1744+
case tDefs => Block(tDefs, typ())
1745+
1746+
def quotePatternTypeVars(): List[Tree] =
1747+
val tDefs = new ListBuffer[Tree]
1748+
while in.token == TYPE do
1749+
val mods = defAnnotsMods(BitSet())
1750+
tDefs += typeDefOrDcl(in.offset, in.skipToken(mods))
1751+
if in.token == SEMI then in.nextToken()
1752+
if in.isNewLine then in.nextToken()
1753+
tDefs.toList
1754+
17381755
/** ExprSplice ::= ‘$’ spliceId -- if inside quoted block
17391756
* | ‘$’ ‘{’ Block ‘}’ -- unless inside quoted pattern
17401757
* | ‘$’ ‘{’ Pattern ‘}’ -- when inside quoted pattern
@@ -2496,7 +2513,7 @@ object Parsers {
24962513
atSpan(in.skipToken()) {
24972514
withinStaged(StageKind.Quoted | (if (location.inPattern) StageKind.QuotedPattern else 0)) {
24982515
val body =
2499-
if (in.token == LBRACKET) inBrackets(typ())
2516+
if (in.token == LBRACKET) inBrackets(typeBlock())
25002517
else stagedBlock()
25012518
Quote(body)
25022519
}
@@ -3762,6 +3779,8 @@ object Parsers {
37623779
else makeTypeDef(bounds)
37633780
case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
37643781
makeTypeDef(typeBounds())
3782+
case _ if (staged & StageKind.QuotedPattern) != 0 => // is in a quoted pattern
3783+
makeTypeDef(typeBounds())
37653784
case _ =>
37663785
syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
37673786
return EmptyTree // return to avoid setting the span to EmptyTree

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

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -213,11 +213,11 @@ trait QuotesAndSplices {
213213
* )
214214
* ```
215215
*/
216-
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Bind], Tree, List[Tree]) = {
216+
private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Tree], Tree, List[Tree]) = {
217217
val ctx0 = ctx
218218

219-
val typeBindings: collection.mutable.Map[Symbol, Bind] = collection.mutable.Map.empty
220-
def getBinding(sym: Symbol): Bind =
219+
val typeBindings: collection.mutable.Map[Symbol, Tree] = collection.mutable.Map.empty
220+
def getBinding(sym: Symbol): Tree =
221221
typeBindings.getOrElseUpdate(sym, {
222222
val bindingBounds = sym.info
223223
val bsym = newPatternBoundSymbol(sym.name.toString.stripPrefix("$").toTypeName, bindingBounds, quoted.span)
@@ -408,6 +408,12 @@ trait QuotesAndSplices {
408408
}
409409
val (untpdTypeVariables, quoted0) = desugar.quotedPatternTypeVariables(desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt))))
410410

411+
if quoted.isType && untpdTypeVariables.nonEmpty then
412+
checkExperimentalFeature(
413+
"explicit type variable declarations quoted type patterns (SIP-53)",
414+
untpdTypeVariables.head.srcPos,
415+
"\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
416+
411417
val (typeTypeVariables, patternCtx) =
412418
val quoteCtx = quotePatternContext()
413419
if untpdTypeVariables.isEmpty then (Nil, quoteCtx)
@@ -418,7 +424,7 @@ trait QuotesAndSplices {
418424
addQuotedPatternTypeVariable(typeVariable.symbol)
419425

420426
val pattern =
421-
if quoted.isType then typedType(quoted0, WildcardType)
427+
if quoted.isType then typedType(quoted0, WildcardType)(using patternCtx)
422428
else typedExpr(quoted0, WildcardType)
423429

424430
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/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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