IDEA-131953 Multiple carets misbehave when auto completion dropdown opens

java/java-tests/testSrc/com/intellij/codeInsight/completion/JavaAutoPopupTest.groovy

@@ -650,6 +650,47 @@ public interface Test {
     assert !lookup
   }
 
+  public void testMulticaretLeftRightMovements() {
+    myFixture.configureByText("a.java", """
+      class Foo {
+        void foo(String iterable) {
+          <caret>ter   x
+          <caret>ter   x
+        }
+      }
+    """)
+    type('i')
+    assert lookup
+
+    edt { myFixture.performEditorAction(IdeActions.ACTION_EDITOR_MOVE_CARET_RIGHT) }
+    myFixture.checkResult """
+      class Foo {
+        void foo(String iterable) {
+          it<caret>er   x
+          it<caret>er   x
+        }
+      }
+    """
+    joinAutopopup()
+    joinCompletion()
+    assert lookup
+    assert !lookup.calculating
+
+    edt { myFixture.performEditorAction(IdeActions.ACTION_EDITOR_MOVE_CARET_LEFT) }
+    myFixture.checkResult """
+      class Foo {
+        void foo(String iterable) {
+          i<caret>ter   x
+          i<caret>ter   x
+        }
+      }
+    """
+    joinAutopopup()
+    joinCompletion()
+    assert lookup
+    assert !lookup.calculating
+  }
+
   public void testTypingInAnotherEditor() {
     myFixture.configureByText("a.java", "")
     type 'c'

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupActionHandler.java

@@ -26,6 +26,7 @@ import com.intellij.featureStatistics.FeatureUsageTracker;
 import com.intellij.ide.ui.UISettings;
 import com.intellij.openapi.actionSystem.*;
 import com.intellij.openapi.editor.Caret;
+import com.intellij.openapi.editor.CaretAction;
 import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.editor.actionSystem.EditorActionHandler;
 import com.intellij.openapi.project.DumbAwareAction;
@@ -211,7 +212,7 @@ public abstract class LookupActionHandler extends EditorActionHandler {
     }
 
     @Override
-    protected void executeInLookup(LookupImpl lookup, DataContext context, Caret caret) {
+    protected void executeInLookup(LookupImpl lookup, DataContext context, final Caret caret) {
       final Editor editor = lookup.getEditor();
       final int offset = editor.getCaretModel().getOffset();
       CharSequence seq = editor.getDocument().getCharsSequence();
@@ -231,8 +232,19 @@ public abstract class LookupActionHandler extends EditorActionHandler {
       if (!lookup.performGuardedChange(new Runnable() {
         @Override
         public void run() {
-          editor.getSelectionModel().removeSelection();
-          editor.getCaretModel().moveToOffset(offset + 1);
+          CaretAction action = new CaretAction() {
+            @Override
+            public void perform(Caret caret) {
+              caret.removeSelection();
+              caret.moveToOffset(caret.getOffset() + 1);
+            }
+          };
+          if (caret == null) {
+            editor.getCaretModel().runForEachCaret(action);
+          }
+          else {
+            action.perform(caret);
+          }
         }
       })) {
         return;