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

Author: nicolasstucki

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

@@ -1633,6 +1633,19 @@ object Parsers {
             t
     end typ
 
+    /** TypeBlock ::= {TypeBlockStat semi} Type
+     *  TypeBlockStat     ::=  ‘type’ {nl} TypeDcl
+     */
+    def typeBlock(): Tree =
+      val tDefs = new ListBuffer[Tree]
+      while in.token == TYPE do
+        val mods = defAnnotsMods(modifierTokens)
+        tDefs += typeDefOrDcl(in.offset, in.skipToken(mods))
+        acceptStatSep()
+      val tpt = typ()
+      if tDefs.isEmpty then tpt else Block(tDefs.toList, tpt)
+
+
     private def makeKindProjectorTypeDef(name: TypeName): TypeDef = {
       val isVarianceAnnotated = name.startsWith("+") || name.startsWith("-")
       // We remove the variance marker from the name without passing along the specified variance at all
@@ -2496,7 +2509,7 @@ object Parsers {
           atSpan(in.skipToken()) {
             withinStaged(StageKind.Quoted | (if (location.inPattern) StageKind.QuotedPattern else 0)) {
               Quote {
-                if (in.token == LBRACKET) inBrackets(typ())
+                if (in.token == LBRACKET) inBrackets(typeBlock())
                 else stagedBlock()
               }
             }

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

@@ -210,11 +210,11 @@ trait QuotesAndSplices {
    *  )
    *  ```
    */
-  private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Bind], Tree, List[Tree]) = {
+  private def splitQuotePattern(quoted: Tree)(using Context): (Map[Symbol, Tree], Tree, List[Tree]) = {
     val ctx0 = ctx
 
-    val typeBindings: collection.mutable.Map[Symbol, Bind] = collection.mutable.Map.empty
-    def getBinding(sym: Symbol): Bind =
+    val typeBindings: collection.mutable.Map[Symbol, Tree] = collection.mutable.Map.empty
+    def getBinding(sym: Symbol): Tree =
       typeBindings.getOrElseUpdate(sym, {
         val bindingBounds = sym.info
         val bsym = newPatternBoundSymbol(sym.name.toString.stripPrefix("$").toTypeName, bindingBounds, quoted.span)
@@ -407,6 +407,12 @@ trait QuotesAndSplices {
     }
     val (untpdTypeVariables, quoted0) = desugar.quotedPatternTypeVariables(desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt))))
 
+    if quoted.isType && untpdTypeVariables.nonEmpty then
+      checkExperimentalFeature(
+        "explicit type variable declarations quoted type patterns (SIP-53)",
+        untpdTypeVariables.head.srcPos,
+        "\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
+
     val (typeTypeVariables, patternCtx) =
       val quoteCtx = quotePatternContext()
       if untpdTypeVariables.isEmpty then (Nil, quoteCtx)
@@ -417,7 +423,7 @@ trait QuotesAndSplices {
         addQuotedPatternTypeVariable(typeVariable.symbol)
 
       val pattern =
-        if quoted.isType then typedType(quoted0, WildcardType)
+        if quoted.isType then typedType(quoted0, WildcardType)(using patternCtx)
         else typedExpr(quoted0, WildcardType)
 
       if untpdTypeVariables.isEmpty then pattern

docs/_docs/reference/metaprogramming/macros.md

@@ -530,15 +530,24 @@ It works the same way as a quoted pattern but is restricted to contain a type.
 Type variables can be used in quoted type patterns to extract a type.
 
 ```scala
-def empty[T: Type]: Expr[T] =
+def empty[T: Type](using Quotes): Expr[T] =
   Type.of[T] match
     case '[String] => '{ "" }
     case '[List[t]] => '{ List.empty[t] }
+    case '[type t <: Option[Int]; List[t]] => '{ List.empty[t] }
     ...
 ```
-
 `Type.of[T]` is used to summon the given instance of `Type[T]` in scope, it is equivalent to `summon[Type[T]]`.
 
+It is possible to match against a higer-kinded type using appropriate type bounds on type variables.
+```scala
+def empty[K <: AnyKind : Type](using Quotes): Type[?] =
+  Type.of[K] match
+    case '[type f[X]; f] => Type.of[f]
+    case '[type f[X <: Int, Y]; f] => Type.of[f]
+    case '[type k <: AnyKind; k ] => Type.of[k]
+```
+
 #### Type testing and casting
 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.
 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

@@ -274,7 +274,7 @@ ColonArgument     ::=  colon [LambdaStart]
 LambdaStart       ::=  FunParams (‘=>’ | ‘?=>’)
                     |  HkTypeParamClause ‘=>’
 Quoted            ::=  ‘'’ ‘{’ Block ‘}’
-                    |  ‘'’ ‘[’ Type ‘]’
+                    |  ‘'’ ‘[’ TypeBlock ‘]’
 ExprSplice        ::= spliceId                                                  -- if inside quoted block
                     |  ‘$’ ‘{’ Block ‘}’                                        -- unless inside quoted pattern
                     |  ‘$’ ‘{’ Pattern ‘}’                                      -- when inside quoted pattern
@@ -293,6 +293,8 @@ BlockStat         ::=  Import
                     |  Extension
                     |  Expr1
                     |  EndMarker
+TypeBlock         ::=  {TypeBlockStat semi} Type
+TypeBlockStat     ::=  ‘type’ {nl} TypeDcl
 
 ForExpr           ::=  ‘for’ ‘(’ Enumerators0 ‘)’ {nl} [‘do‘ | ‘yield’] Expr
                     |  ‘for’ ‘{’ Enumerators0 ‘}’ {nl} [‘do‘ | ‘yield’] Expr

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

@@ -0,0 +1,8 @@
+import scala.quoted.*
+
+def empty[K <: AnyKind : Type](using Quotes): Type[?] =
+  Type.of[K] match
+    case '[type t; `t`] => Type.of[t] // error
+    case '[type f[X]; `f`] => Type.of[f] // error
+    case '[type f[X <: Int, Y]; `f`] => Type.of[f] // error
+    case '[type k <: AnyKind; `k` ] => Type.of[k] // error

tests/pos-macros/i10864/Macro_1.scala

@@ -0,0 +1,15 @@
+import scala.quoted._
+
+case class T(t: Type[_])
+
+object T {
+  def impl[T <: AnyKind](using tt: Type[T])(using Quotes): Expr[Unit] = {
+    val t = T(tt)
+    t.t match
+      case '[type x <: AnyKind; x] => // ok
+      case _ => quotes.reflect.report.error("not ok :(")
+    '{}
+  }
+
+  inline def run[T <: AnyKind] = ${ impl[T] }
+}

tests/pos-macros/i10864/Test_2.scala

@@ -0,0 +1,4 @@
+def test =
+  T.run[List]
+  T.run[Map]
+  T.run[Tuple22]

tests/pos-macros/i10864a/Macro_1.scala

@@ -0,0 +1,21 @@
+import scala.quoted._
+
+case class T(t: Type[_])
+
+object T {
+  def impl[T <: AnyKind](using tt: Type[T])(using Quotes): Expr[Unit] = {
+    val t = T(tt)
+    t.t match
+      case '[type x; x] =>
+        assert(Type.show[x] == "scala.Int", Type.show[x])
+      case '[type f[X]; f] =>
+        assert(Type.show[f] == "[A >: scala.Nothing <: scala.Any] => scala.collection.immutable.List[A]", Type.show[f])
+      case '[type f[X <: Int]; f] =>
+        assert(Type.show[f] == "[T >: scala.Nothing <: scala.Int] => C[T]", Type.show[f])
+      case '[type f <: AnyKind; f] =>
+        assert(Type.show[f] == "[K >: scala.Nothing <: scala.Any, V >: scala.Nothing <: scala.Any] => scala.collection.immutable.Map[K, V]", Type.show[f])
+    '{}
+  }
+
+  inline def run[T <: AnyKind] = ${ impl[T] }
+}

tests/pos-macros/i10864a/Test_2.scala

@@ -0,0 +1,8 @@
+@main
+def run =
+  T.run[Int]
+  T.run[C]
+  T.run[List]
+  T.run[Map]
+
+class C[T <: Int]

tests/pos-macros/i11738.scala

@@ -0,0 +1,8 @@
+import scala.quoted.*
+
+def blah[A](using Quotes, Type[A]): Expr[Unit] =
+  Type.of[A] match
+    case '[h *: t] => println(s"h = ${Type.show[h]}, t = ${Type.show[t]}") // ok
+    case '[type f[X]; f[a]]   => println(s"f = ${Type.show[f]}, a = ${Type.show[a]}") // error
+    case _         =>
+  '{()}

tests/pos-macros/i7264.scala

@@ -3,5 +3,6 @@ class Foo {
   def f[T2](t: Type[T2])(using Quotes) = t match {
     case '[ *:[Int, t2] ] =>
       Type.of[ *:[Int, t2] ]
+    case '[ type t <: Tuple; *:[t, t] ] =>
   }
 }