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

@@ -1632,6 +1632,19 @@ 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
@@ -2495,7 +2508,7 @@ 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

@@ -198,11 +198,11 @@ 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)
@@ -396,7 +396,10 @@ trait QuotesAndSplices {
     val quoted0 = desugar.quotedPattern(quoted, untpd.TypedSplice(TypeTree(quotedPt)))
     val quoteCtx = quoteContext.addMode(Mode.QuotedPattern).retractMode(Mode.Pattern)
     val quoted1 =
-      if quoted.isType then typedType(quoted0, WildcardType)(using quoteCtx)
+      if quoted.isType then typedType(quoted0, WildcardType)(using quoteCtx) match
+        case quoted1 @ Block(stats, Typed(tpt, _)) => cpy.Block(quoted1)(stats, tpt)
+        case quoted1 => quoted1
+
       else typedExpr(quoted0, WildcardType)(using quoteCtx)
 
     val (typeBindings, shape, splices) = splitQuotePattern(quoted1)

docs/_docs/reference/metaprogramming/macros.md

@@ -530,6 +530,7 @@ def empty[T: Type]: Expr[T] =
   Type.of[T] match
     case '[String] => '{ "" }
     case '[List[t]] => '{ List.empty[t] }
+    case '[type t <: Option[Int]; List[`t`]] => '{ List.empty[t] }
     ...
 ```
 

docs/_docs/reference/syntax.md

@@ -277,7 +277,7 @@ 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
@@ -296,6 +296,8 @@ 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/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 +1,19 @@
+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 <: 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 +1,5 @@
+@main
+def run =
+  T.run[Int]
+  T.run[List]
+  T.run[Map]

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`] ] =>
   }
 }