diff --git a/compiler/src/dotty/tools/dotc/ast/Positioned.scala b/compiler/src/dotty/tools/dotc/ast/Positioned.scala
index 4de57def853e..d14addb8c9c7 100644
--- a/compiler/src/dotty/tools/dotc/ast/Positioned.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Positioned.scala
@@ -32,9 +32,9 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
     if ids != null then
       val ownId = nextId
       nextId += 1
-      ids.nn.put(this, ownId)
+      ids.nn.put(this: @unchecked, ownId)
       if ownId == debugId then
-        println(s"Debug tree (id=$debugId) creation \n$this\n")
+        println(s"Debug tree (id=$debugId) creation \n${this: @unchecked}\n")
         Thread.dumpStack()
 
   allocateId()
@@ -83,7 +83,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
    *  the left, or, if that one does not exist, to the start position of the envelope
    *  of all children to the right.
    */
-  def envelope(src: SourceFile, startSpan: Span = NoSpan): Span = this match {
+  def envelope(src: SourceFile, startSpan: Span = NoSpan): Span = (this: @unchecked) match {
     case Trees.Inlined(call, _, _) =>
       call.span
     case _ =>
@@ -106,7 +106,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
       }
       val limit = productArity
       def includeChildren(span: Span, n: Int): Span =
-        if (n < limit) includeChildren(include(span, productElement(n)), n + 1)
+        if (n < limit) includeChildren(include(span, productElement(n): @unchecked), n + 1)
         else span
       val span1 = includeChildren(startSpan, 0)
       val span2 =
diff --git a/compiler/src/dotty/tools/dotc/core/Contexts.scala b/compiler/src/dotty/tools/dotc/core/Contexts.scala
index 2f82c85ba9a0..3dfafe6837d0 100644
--- a/compiler/src/dotty/tools/dotc/core/Contexts.scala
+++ b/compiler/src/dotty/tools/dotc/core/Contexts.scala
@@ -819,7 +819,7 @@ object Contexts {
 
   @sharable object NoContext extends Context((null: ContextBase | Null).uncheckedNN) {
     source = NoSource
-    override val implicits: ContextualImplicits = new ContextualImplicits(Nil, null, false)(this)
+    override val implicits: ContextualImplicits = new ContextualImplicits(Nil, null, false)(this: @unchecked)
   }
 
   /** A context base defines state and associated methods that exist once per
diff --git a/compiler/src/dotty/tools/dotc/core/NameKinds.scala b/compiler/src/dotty/tools/dotc/core/NameKinds.scala
index 0e9ccecb18c8..f71c16e82b70 100644
--- a/compiler/src/dotty/tools/dotc/core/NameKinds.scala
+++ b/compiler/src/dotty/tools/dotc/core/NameKinds.scala
@@ -85,7 +85,7 @@ object NameKinds {
       case _ => None
     }
 
-    simpleNameKinds(tag) = this
+    simpleNameKinds(tag) = this: @unchecked
   }
 
   /** The kind of names that get formed by adding a prefix to an underlying name */
@@ -152,7 +152,7 @@ object NameKinds {
 
     def infoString: String = s"Qualified $separator"
 
-    qualifiedNameKinds(tag) = this
+    qualifiedNameKinds(tag) = this: @unchecked
   }
 
   /** An extractor for qualified names of an arbitrary kind */
@@ -190,7 +190,7 @@ object NameKinds {
       else -1
     }
 
-    numberedNameKinds(tag) = this
+    numberedNameKinds(tag) = this: @unchecked
   }
 
   /** An extractor for numbered names of arbitrary kind */
@@ -225,7 +225,7 @@ object NameKinds {
     def fresh(prefix: TypeName)(using Context): TypeName =
       fresh(prefix.toTermName).toTypeName
 
-    uniqueNameKinds(separator) = this
+    uniqueNameKinds(separator) = this: @unchecked
   }
 
   /** An extractor for unique names of arbitrary kind */
diff --git a/compiler/src/dotty/tools/dotc/core/Names.scala b/compiler/src/dotty/tools/dotc/core/Names.scala
index a185ad252073..4cf7d17c17db 100644
--- a/compiler/src/dotty/tools/dotc/core/Names.scala
+++ b/compiler/src/dotty/tools/dotc/core/Names.scala
@@ -568,7 +568,7 @@ object Names {
           enterIfNew(cs, offset, len)
       }
 
-    addEntryAt(0, EmptyTermName)
+    addEntryAt(0, EmptyTermName: @unchecked)
   end NameTable
 
   /** Hashtable for finding term names quickly. */
diff --git a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
index bf1fe4194c96..082112d800d9 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
@@ -162,7 +162,7 @@ object Scanners {
         errorButContinue("trailing separator is not allowed", offset + litBuf.length - 1)
   }
 
-  class Scanner(source: SourceFile, override val startFrom: Offset = 0, profile: Profile = NoProfile)(using Context) extends ScannerCommon(source) {
+  class Scanner(source: SourceFile, override val startFrom: Offset = 0, profile: Profile = NoProfile, allowIndent: Boolean = true)(using Context) extends ScannerCommon(source) {
     val keepComments = !ctx.settings.YdropComments.value
 
     /** A switch whether operators at the start of lines can be infix operators */
@@ -185,10 +185,7 @@ object Scanners {
     val indentSyntax =
       ((if (Config.defaultIndent) !noindentSyntax else ctx.settings.indent.value)
        || rewriteNoIndent)
-      && { this match
-        case self: LookaheadScanner => self.allowIndent
-        case _ => true
-      }
+      && allowIndent
 
     if (rewrite) {
       val s = ctx.settings
@@ -1093,7 +1090,7 @@ object Scanners {
         reset()
       next
 
-    class LookaheadScanner(val allowIndent: Boolean = false) extends Scanner(source, offset) {
+    class LookaheadScanner(val allowIndent: Boolean = false) extends Scanner(source, offset, allowIndent = allowIndent) {
       override def languageImportContext = Scanner.this.languageImportContext
     }
 
diff --git a/compiler/src/dotty/tools/dotc/profile/Profiler.scala b/compiler/src/dotty/tools/dotc/profile/Profiler.scala
index 0533b6bdaec3..0283fb904476 100644
--- a/compiler/src/dotty/tools/dotc/profile/Profiler.scala
+++ b/compiler/src/dotty/tools/dotc/profile/Profiler.scala
@@ -100,10 +100,6 @@ private [profile] class RealProfiler(reporter : ProfileReporter)(using Context)
   def outDir: AbstractFile = ctx.settings.outputDir.value
 
   val id: Int = RealProfiler.idGen.incrementAndGet()
-  RealProfiler.gcMx foreach {
-    case emitter: NotificationEmitter => emitter.addNotificationListener(this, null, null)
-    case gc => println(s"Cant connect gcListener to ${gc.getClass}")
-  }
 
   private val mainThread = Thread.currentThread()
 
@@ -130,6 +126,11 @@ private [profile] class RealProfiler(reporter : ProfileReporter)(using Context)
     System.runFinalization()
   }
 
+  RealProfiler.gcMx foreach {
+    case emitter: NotificationEmitter => emitter.addNotificationListener(this, null, null)
+    case gc => println(s"Cant connect gcListener to ${gc.getClass}")
+  }
+
   reporter.header(this)
 
   override def finished(): Unit = {
diff --git a/compiler/src/dotty/tools/dotc/transform/ForwardDepChecks.scala b/compiler/src/dotty/tools/dotc/transform/ForwardDepChecks.scala
index 0de1a523d265..bf8a6fa6c7bf 100644
--- a/compiler/src/dotty/tools/dotc/transform/ForwardDepChecks.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ForwardDepChecks.scala
@@ -31,7 +31,7 @@ object ForwardDepChecks:
       stats.foldLeft(outer.levelAndIndex, 0) {(mi, stat) =>
         val (m, idx) = mi
         val m1 = stat match {
-          case stat: MemberDef => m.updated(stat.symbol, (this, idx))
+          case stat: MemberDef => m.updated(stat.symbol, (this: @unchecked, idx))
           case _ => m
         }
         (m1, idx + 1)