IJPL-207762 introduce frontend-friendly tail types

GitOrigin-RevId: 1dc3f250ae1c85f4453ec4b337b37ff8e8f0cfcc

java/java-frontback-impl/resource/intellij.java.frontback.impl.xml

@@ -97,5 +97,7 @@
 
     <codeInsight.completion.command.factory language="JAVA" implementationClass="com.intellij.codeInsight.completion.commands.JavaCommandCompletionFactory" />
 
+    <completion.frontendFriendlyInsertHandler target="com.intellij.codeInsight.completion.FrontendFriendlyOverridableSpaceInsertHandler"/>
+
   </extensions>
 </idea-plugin>

java/java-frontback-impl/src/com/intellij/codeInsight/completion/FrontendFriendlyOverridableSpaceInsertHandler.kt

@@ -0,0 +1,45 @@
+// Copyright 2000-2026 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.codeInsight.completion
+
+import com.intellij.codeInsight.TailType
+import com.intellij.codeInsight.completion.serialization.InsertHandlerSerializer
+import com.intellij.codeInsight.completion.serialization.TailTypeSerializer
+import com.intellij.codeInsight.lookup.LookupElement
+import com.intellij.codeInsight.lookup.LookupElementBuilder
+import kotlinx.serialization.Serializable
+
+
+@Serializable
+internal data class FrontendFriendlyOverridableSpaceInsertHandler(
+  val delegateInsertHandler: FrontendFriendlyInsertHandler?,
+  val tailType: FrontendFriendlyTailType,
+) : FrontendFriendlyInsertHandler {
+
+  override fun handleInsert(context: InsertionContext, item: LookupElement) {
+    require(tailType is TailType) { "Tail type must extend TailType: $tailType" }
+    val wrapper = LookupElementBuilder.create("").withInsertHandler(delegateInsertHandler)
+    val lookupElement = OverridableSpace.create(wrapper, tailType)
+    lookupElement.handleInsert(context)
+  }
+
+  companion object {
+    @JvmStatic
+    fun createIfFrontendFriendly(os: OverridableSpace): FrontendFriendlyOverridableSpaceInsertHandler? {
+      // Try to convert tail type to frontend-friendly version
+      val tail = os.myTail
+      val ffTailType = tail as? FrontendFriendlyTailType ?: TailTypeSerializer.toDescriptor(tail) ?: return null
+
+      // Try to get delegate's effective handler
+      val delegateHandler = os.delegateEffectiveInsertHandler
+      val ffDelegate = if (delegateHandler != null) {
+        delegateHandler as? FrontendFriendlyInsertHandler ?: InsertHandlerSerializer.toDescriptor(delegateHandler)
+        ?: return null // delegate handler must be frontend-friendly
+      }
+      else {
+        null // missing delegate handler is OK
+      }
+
+      return FrontendFriendlyOverridableSpaceInsertHandler(ffDelegate, ffTailType)
+    }
+  }
+}

java/java-frontback-impl/src/com/intellij/codeInsight/completion/OverridableSpace.java

@@ -6,9 +6,10 @@ import com.intellij.codeInsight.TailTypes;
 import com.intellij.codeInsight.lookup.LookupElement;
 import com.intellij.codeInsight.lookup.TailTypeDecorator;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
-public final class OverridableSpace extends TailTypeDecorator<LookupElement> {
-  private final @NotNull TailType myTail;
+public final class OverridableSpace extends TailTypeDecorator<LookupElement> implements LookupElementWithEffectiveInsertHandler {
+  final @NotNull TailType myTail;
 
   private OverridableSpace(@NotNull LookupElement keyword, @NotNull TailType tail) {
     super(keyword);
@@ -20,6 +21,16 @@ public final class OverridableSpace extends TailTypeDecorator<LookupElement> {
     return context.shouldAddCompletionChar() ? TailTypes.noneType() : myTail;
   }
 
+  @Override
+  protected @Nullable InsertHandler<?> getDelegateEffectiveInsertHandler() {
+    return super.getDelegateEffectiveInsertHandler();
+  }
+
+  @Override
+  public @Nullable InsertHandler<?> getEffectiveInsertHandler() {
+    return FrontendFriendlyOverridableSpaceInsertHandler.createIfFrontendFriendly(this);
+  }
+
   public static LookupElement create(@NotNull LookupElement delegate, @NotNull TailType tail) {
     return new OverridableSpace(delegate, tail);
   }