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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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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
@@ -2496,7 +2517,7 @@ object Parsers {
24962517
atSpan(in.skipToken()) {
24972518
withinStaged(StageKind.Quoted | (if (location.inPattern) StageKind.QuotedPattern else 0)) {
24982519
val body =
2499-
if (in.token == LBRACKET) inBrackets(typ())
2520+
if (in.token == LBRACKET) inBrackets(typeBlock())
25002521
else stagedBlock()
25012522
Quote(body)
25022523
}
@@ -3762,6 +3783,8 @@ object Parsers {
37623783
else makeTypeDef(bounds)
37633784
case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
37643785
makeTypeDef(typeBounds())
3786+
case _ if (staged & StageKind.QuotedPattern) != 0 =>
3787+
makeTypeDef(typeBounds())
37653788
case _ =>
37663789
syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
37673790
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
@@ -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 +408,17 @@ trait QuotesAndSplices {
408408
}
409409
val (untpdTypeVariables, quoted0) = desugar.quotedPatternTypeVariables(desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt))))
410410

411+
for untpdTypeVariable <- untpdTypeVariables do untpdTypeVariable.rhs match
412+
case _: TypeBoundsTree => // ok
413+
case LambdaTypeTree(_, body: TypeBoundsTree) => // ok
414+
case _ => report.error("Quote type variable definition cannot be an alias", untpdTypeVariable.srcPos)
415+
416+
if quoted.isType && untpdTypeVariables.nonEmpty then
417+
checkExperimentalFeature(
418+
"explicit type variable declarations quoted type patterns (SIP-53)",
419+
untpdTypeVariables.head.srcPos,
420+
"\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
421+
411422
val (typeTypeVariables, patternCtx) =
412423
val quoteCtx = quotePatternContext()
413424
if untpdTypeVariables.isEmpty then (Nil, quoteCtx)
@@ -418,7 +429,7 @@ trait QuotesAndSplices {
418429
addQuotedPatternTypeVariable(typeVariable.symbol)
419430

420431
val pattern =
421-
if quoted.isType then typedType(quoted0, WildcardType)
432+
if quoted.isType then typedType(quoted0, WildcardType)(using patternCtx)
422433
else typedExpr(quoted0, WildcardType)
423434

424435
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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