diff --git a/compiler/src/dotty/tools/dotc/interactive/Completion.scala b/compiler/src/dotty/tools/dotc/interactive/Completion.scala
index bd2a1af2ed1c..954b56ea1c54 100644
--- a/compiler/src/dotty/tools/dotc/interactive/Completion.scala
+++ b/compiler/src/dotty/tools/dotc/interactive/Completion.scala
@@ -21,6 +21,7 @@ import dotty.tools.dotc.core.TypeComparer
 import dotty.tools.dotc.core.TypeError
 import dotty.tools.dotc.core.Types.{ExprType, MethodOrPoly, NameFilter, NamedType, NoType, PolyType, TermRef, Type}
 import dotty.tools.dotc.printing.Texts._
+import dotty.tools.dotc.util.Chars.{isOperatorPart, isScalaLetter}
 import dotty.tools.dotc.util.{NameTransformer, NoSourcePosition, SourcePosition}
 
 import scala.collection.mutable
@@ -59,7 +60,7 @@ object Completion {
    *
    * Otherwise, provide no completion suggestion.
    */
-  private def completionMode(path: List[Tree], pos: SourcePosition): Mode =
+  def completionMode(path: List[Tree], pos: SourcePosition): Mode =
     path match {
       case (ref: RefTree) :: _ =>
         if (ref.name.isTermName) Mode.Term
@@ -81,7 +82,7 @@ object Completion {
    * Inspect `path` to determine the completion prefix. Only symbols whose name start with the
    * returned prefix should be considered.
    */
-  private def completionPrefix(path: List[untpd.Tree], pos: SourcePosition): String =
+  def completionPrefix(path: List[untpd.Tree], pos: SourcePosition): String =
     path match {
       case (sel: untpd.ImportSelector) :: _ =>
         completionPrefix(sel.imported :: Nil, pos)
@@ -100,7 +101,7 @@ object Completion {
     }
 
   /** Inspect `path` to determine the offset where the completion result should be inserted. */
-  private def completionOffset(path: List[Tree]): Int =
+  def completionOffset(path: List[Tree]): Int =
     path match {
       case (ref: RefTree) :: _ => ref.span.point
       case _ => 0
@@ -134,14 +135,14 @@ object Completion {
    * If several denotations share the same name, the type denotations appear before term denotations inside
    * the same `Completion`.
    */
-  private def describeCompletions(completions: CompletionMap)(using Context): List[Completion] = {
+  def describeCompletions(completions: CompletionMap)(using Context): List[Completion] = {
     completions
       .toList.groupBy(_._1.toTermName) // don't distinguish between names of terms and types
       .toList.map { (name, namedDenots) =>
         val denots = namedDenots.flatMap(_._2)
         val typesFirst = denots.sortWith((d1, d2) => d1.isType && !d2.isType)
         val desc = description(typesFirst)
-        Completion(name.show, desc, typesFirst.map(_.symbol))
+        Completion(label(name), desc, typesFirst.map(_.symbol))
     }
   }
 
@@ -174,7 +175,7 @@ object Completion {
    *  For the results of all `xyzCompletions` methods term names and type names are always treated as different keys in the same map
    *  and they never conflict with each other.
    */
-  private class Completer(val mode: Mode, val prefix: String, pos: SourcePosition) {
+  class Completer(val mode: Mode, val prefix: String, pos: SourcePosition) {
     /** Completions for terms and types that are currently in scope:
      *  the members of the current class, local definitions and the symbols that have been imported,
      *  recursively adding completions from outer scopes.
@@ -442,11 +443,11 @@ object Completion {
    * The completion mode: defines what kinds of symbols should be included in the completion
    * results.
    */
-  private class Mode(val bits: Int) extends AnyVal {
+  class Mode(val bits: Int) extends AnyVal {
     def is(other: Mode): Boolean = (bits & other.bits) == other.bits
     def |(other: Mode): Mode = new Mode(bits | other.bits)
   }
-  private object Mode {
+  object Mode {
     /** No symbol should be included */
     val None: Mode = new Mode(0)
 
@@ -459,5 +460,39 @@ object Completion {
     /** Both term and type symbols are allowed */
     val Import: Mode = new Mode(4) | Term | Type
   }
+
+  private val bslash = '\\'
+  private val isDot = (x: Char) => x == '.'
+  private val brackets = List('[',']','(',')','{','}')
+
+  def label(name: Name): String = {
+
+    def maybeQuote(name: Name, recurse: Boolean): String =
+      if (recurse && name.isTermName)
+        name.asTermName.qualToString(maybeQuote(_, true), maybeQuote(_, false))
+      // initially adapted from
+      // https://github.com/scala/scala/blob/decbd53f1bde4600c8ff860f30a79f028a8e431d/
+      //   src/reflect/scala/reflect/internal/Printers.scala#L573-L584
+      else if (name == nme.CONSTRUCTOR) "this"
+      else {
+        val decName = name.decode.toString
+        val hasSpecialChar = decName.exists { ch =>
+          brackets.contains(ch) || ch.isWhitespace || isDot(ch)
+        }
+        def isOperatorLike = (name.isOperatorName || decName.exists(isOperatorPart)) &&
+          decName.exists(isScalaLetter) &&
+          !decName.contains(bslash)
+        lazy val term = name.toTermName
+
+        val needsBackTicks = hasSpecialChar ||
+          isOperatorLike ||
+          nme.keywords(term) && term != nme.USCOREkw
+
+        if (needsBackTicks) s"`$decName`"
+        else decName
+      }
+
+    maybeQuote(name, true)
+  }
 }
 
diff --git a/compiler/test/dotty/tools/dotc/interactive/CompletionTests.scala b/compiler/test/dotty/tools/dotc/interactive/CompletionTests.scala
new file mode 100644
index 000000000000..629caf9e51e2
--- /dev/null
+++ b/compiler/test/dotty/tools/dotc/interactive/CompletionTests.scala
@@ -0,0 +1,152 @@
+package dotty.tools
+package dotc.interactive
+
+import dotc.ast.tpd
+import dotc.{CompilationUnit, Compiler, Run}
+import dotc.core.Contexts.Context
+import dotc.core.Mode
+import dotc.reporting.StoreReporter
+import dotc.util.{SourceFile, SourcePosition}
+import dotc.util.Spans.Span
+
+import org.junit.Assert._
+import org.junit.Test
+
+class CompletionTests extends DottyTest:
+
+   private def completions(
+     input: String,
+     dependencyCompleter: Option[String => (Int, Seq[String])] = None,
+     deep: Boolean = false
+   ): (Int, Seq[Completion]) =
+      val prefix = """
+        object Wrapper {
+          val expr = {
+      """
+      val suffix = """
+          }
+        }
+      """
+
+      val allCode = prefix + input + suffix
+      val index = prefix.length + input.length
+
+      val run = new Run(
+        new Compiler,
+        initialCtx.fresh
+          .addMode(Mode.ReadPositions | Mode.Interactive)
+          // discard errors - comment out this line to print them in the console
+          .setReporter(new StoreReporter(null))
+          .setSetting(initialCtx.settings.YstopAfter, List("typer"))
+      )
+      val file = SourceFile.virtual("<completions>", allCode, maybeIncomplete = true)
+      given ctx: Context = run.runContext.withSource(file)
+      val unit = CompilationUnit(file)
+      ctx
+        .run
+        .compileUnits(unit :: Nil, ctx)
+
+      // ignoring compilation errors here - the input code
+      // to complete likely doesn't compile
+
+      unit.tpdTree = {
+        import tpd._
+        unit.tpdTree match {
+          case PackageDef(_, p) =>
+            p.collectFirst {
+              case TypeDef(_, tmpl: Template) =>
+                tmpl.body
+                  .collectFirst { case dd: ValDef if dd.name.show == "expr" => dd }
+                  .getOrElse(sys.error("Unexpected tree shape"))
+            }
+            .getOrElse(sys.error("Unexpected tree shape"))
+          case _ => sys.error("Unexpected tree shape")
+        }
+      }
+      val ctx1 = ctx.fresh.setCompilationUnit(unit)
+      val srcPos = SourcePosition(file, Span(index))
+      val (offset0, completions) =
+        if (deep || dependencyCompleter.nonEmpty)
+          CustomCompletion.completions(srcPos, dependencyCompleteOpt = dependencyCompleter, enableDeep = deep)(using ctx1)
+        else
+          Completion.completions(srcPos)(using ctx1)
+      val offset = offset0 - prefix.length
+      (offset, completions)
+
+
+   @Test def simple(): Unit =
+      val prefix = "scala.collection.immutable."
+      val input = prefix + "Ma"
+
+      val (offset, completions0) = completions(input)
+      val labels = completions0.map(_.label)
+
+      assert(offset == prefix.length)
+      assert(labels.contains("Map"))
+
+   @Test def custom(): Unit =
+      val prefix = "import $ivy."
+      val input = prefix + "scala"
+
+      val dependencies = Seq(
+        "scalaCompiler",
+        "scalaLibrary",
+        "other"
+      )
+      val (offset, completions0) = completions(
+        input,
+        dependencyCompleter = Some { dep =>
+          val matches = dependencies.filter(_.startsWith(dep))
+          (0, matches)
+        }
+      )
+      val labels = completions0.map(_.label)
+
+      assert(offset == prefix.length)
+      assert(labels.contains("scalaCompiler"))
+      assert(labels.contains("scalaLibrary"))
+      assert(labels.length == 2)
+
+   @Test def backTicks(): Unit =
+      val prefix = "import $ivy."
+      val input = prefix + "`org.scala-lang:scala-`"
+
+      val dependencies = Seq(
+        "org.scala-lang:scala-compiler",
+        "org.scala-lang:scala-library",
+        "other"
+      )
+      val (offset, completions0) = completions(
+        input,
+        dependencyCompleter = Some { dep =>
+          val matches = dependencies.filter(_.startsWith(dep))
+          (0, matches)
+        }
+      )
+      val labels = completions0.map(_.label)
+
+      // Seems backticks mess with that for now...
+      // assert(offset == prefix.length)
+      assert(labels.contains("`org.scala-lang:scala-compiler`"))
+      assert(labels.contains("`org.scala-lang:scala-library`"))
+      assert(labels.length == 2)
+
+   @Test def deep(): Unit =
+      val prefix = ""
+      val input = prefix + "ListBuf"
+
+      val (offset, completions0) = completions(input, deep = true)
+      val labels = completions0.map(_.label)
+
+      assert(offset == prefix.length)
+      assert(labels.contains("scala.collection.mutable.ListBuffer"))
+
+   @Test def deepType(): Unit =
+      val prefix = ""
+      val input = prefix + "Function2"
+
+      val (offset, completions0) = completions(input, deep = true)
+      val labels = completions0.map(_.label)
+
+      assert(offset == prefix.length)
+      assert(labels.contains("scala.Function2"))
diff --git a/compiler/test/dotty/tools/dotc/interactive/CustomCompletion.scala b/compiler/test/dotty/tools/dotc/interactive/CustomCompletion.scala
new file mode 100644
index 000000000000..cf1c82c6bce0
--- /dev/null
+++ b/compiler/test/dotty/tools/dotc/interactive/CustomCompletion.scala
@@ -0,0 +1,87 @@
+package dotty.tools.dotc.interactive
+
+import dotty.tools.dotc.ast.tpd._
+import dotty.tools.dotc.ast.untpd
+import dotty.tools.dotc.core.Contexts._
+import dotty.tools.dotc.core.Denotations.SingleDenotation
+import dotty.tools.dotc.core.Flags._
+import dotty.tools.dotc.core.Names.{Name, termName}
+import dotty.tools.dotc.core.Symbols.{Symbol, defn}
+import dotty.tools.dotc.core.TypeError
+import dotty.tools.dotc.util.SourcePosition
+
+object CustomCompletion {
+
+  def completions(
+    pos: SourcePosition,
+    dependencyCompleteOpt: Option[String => (Int, Seq[String])],
+    enableDeep: Boolean
+  )(using Context): (Int, List[Completion]) = {
+    val path = Interactive.pathTo(ctx.compilationUnit.tpdTree, pos.span)
+    computeCompletions(pos, path, dependencyCompleteOpt, enableDeep)(using Interactive.contextOfPath(path))
+  }
+
+  def computeCompletions(
+    pos: SourcePosition,
+    path: List[Tree],
+    dependencyCompleteOpt: Option[String => (Int, Seq[String])],
+    enableDeep: Boolean
+  )(using Context): (Int, List[Completion]) = {
+    val mode = Completion.completionMode(path, pos)
+    val prefix = Completion.completionPrefix(path, pos)
+    val completer = new DeepCompleter(mode, prefix, pos)
+
+    var extra = List.empty[Completion]
+
+    val completions = path match {
+      case Select(qual, _) :: _                              => completer.selectionCompletions(qual)
+      case Import(Ident(name), _) :: _ if name.decode.toString == "$ivy" && dependencyCompleteOpt.nonEmpty =>
+        val complete = dependencyCompleteOpt.get
+        val (pos, completions) = complete(prefix)
+        val input0 = prefix.take(pos)
+        extra ++= completions.distinct.toList
+          .map(s => Completion(Completion.label(termName(input0 + s)), "", Nil))
+        Map.empty
+      case Import(expr, _) :: _                              => completer.directMemberCompletions(expr)
+      case (_: untpd.ImportSelector) :: Import(expr, _) :: _ => completer.directMemberCompletions(expr)
+      case _                                                 =>
+        completer.scopeCompletions ++ {
+          if (enableDeep) completer.deepCompletions
+          else Nil
+        }
+    }
+
+    val describedCompletions = extra ++ Completion.describeCompletions(completions)
+    val offset = Completion.completionOffset(path)
+
+    (pos.span.start - prefix.length, describedCompletions)
+  }
+
+  class DeepCompleter(mode: Completion.Mode, prefix: String, pos: SourcePosition) extends Completion.Completer(mode, prefix, pos):
+    def deepCompletions(using Context): Map[Name, Seq[SingleDenotation]] = {
+
+      def allMembers(s: Symbol) =
+        try s.info.allMembers
+        catch {
+          case _: dotty.tools.dotc.core.TypeError => Nil
+        }
+      def rec(t: Symbol): Seq[Symbol] = {
+        val children =
+          if (t.is(Package) || t.is(PackageVal) || t.is(PackageClass)) {
+            allMembers(t).map(_.symbol).filter(_ != t).flatMap(rec)
+          } else Nil
+
+        t +: children.toSeq
+      }
+
+      val syms = for {
+        member <- allMembers(defn.RootClass).map(_.symbol).toList
+        sym <- rec(member)
+        if sym.name.toString.startsWith(prefix)
+      } yield sym
+
+      syms.map(sym => (sym.fullName, List(sym: SingleDenotation))).toMap
+    }
+
+}
+