Fix scala#21721: make case TypeBlock(_, _) not match non-type Block

TypeBlocks are represented as normal Blocks in the Quotes API. The
current TypeTest for TypeBlock is exactly the same as the TypeTest for
Block, which means that case TypeBlock(_, _) matches every block.

The implementation of unapply on TypeBlockModule, however, gives back
(List[TypeDef], TypeTree). It constructs the List[TypeDef] by mapping
over every statement, turning it into a TypeDef by using a match
with the pattern

  case alias: TypeDef => alias

Since the TypeTest matches any Block and not only Blocks that are
TypeBlocks, the statemnts can be anything, not just TypeDefs, which lets
the whole case TypeBlock(_, _) pattern fail with a MatchError.

This commit fixes the problem by making the TypeTest check whether the
Block is a type (which in turns checks whether the blocks expression is
a type)

[Cherry-picked 147f562]

Author: felher

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -1390,7 +1390,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
 
     object TypeBlockTypeTest extends TypeTest[Tree, TypeBlock]:
       def unapply(x: Tree): Option[TypeBlock & x.type] = x match
-        case tpt: (tpd.Block & x.type) => Some(tpt)
+        case tpt: (tpd.Block & x.type) if x.isType => Some(tpt)
         case _ => None
     end TypeBlockTypeTest
 

tests/pos/i21721/Macro.scala

@@ -0,0 +1,12 @@
+import quoted.*
+
+object Macro:
+  inline def impl(inline expr: Any): Any =
+    ${implImpl('expr)}
+
+  def implImpl(expr: Expr[Any])(using q: Quotes): Expr[Any] =
+    import q.reflect.*
+    expr.asTerm.asInstanceOf[Inlined].body match
+      // this should not fail with a MatchError
+      case TypeBlock(_, _) => '{ "TypeBlock" }
+      case _ => '{ "Nothing" }

tests/pos/i21721/Test.scala

@@ -0,0 +1,5 @@
+object Test:
+  // give a Block(...) to the macro
+  Macro.impl:
+    val a = 3
+    a