autopopup sometimes showed no suggestions

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

@@ -460,5 +460,21 @@ class JavaAutoPopupTest extends CompletionAutoPopupTestCase {
     assert lookup
   }
 
+  public void testHideOnInvalidSymbolAfterBackspace() {
+    myFixture.configureByText("a.java", """
+    class A {
+      Object foo() { this<caret> }
+    }
+    """)
+    type '.'
+    assert lookup
+    type 'c'
+    assert lookup
+    type '\b'
+    assert lookup
+    type 'x'
+    assert !lookup
+  }
+
 
 }

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

@@ -16,9 +16,8 @@
 
 package com.intellij.codeInsight.lookup.impl;
 
-import com.intellij.codeInsight.completion.CompletionProcess;
 import com.intellij.codeInsight.completion.CompletionProgressIndicator;
-import com.intellij.codeInsight.completion.CompletionService;
+import com.intellij.codeInsight.completion.impl.CompletionServiceImpl;
 import com.intellij.codeInsight.lookup.LookupManager;
 import com.intellij.openapi.actionSystem.DataContext;
 import com.intellij.openapi.editor.Editor;
@@ -45,14 +44,14 @@ public class BackspaceHandler extends EditorActionHandler {
       }
     });
 
-    if (lookup.truncatePrefix()) {
+    final CompletionProgressIndicator process = CompletionServiceImpl.getCompletionService().getCurrentCompletion();
+    if (lookup.truncatePrefix(process == null || !process.isAutopopupCompletion())) {
       return;
     }
 
     if (lookup.getLookupStart() < editor.getCaretModel().getOffset()) {
-      final CompletionProcess process = CompletionService.getCompletionService().getCurrentCompletion();
-      if (process instanceof CompletionProgressIndicator) {
-        ((CompletionProgressIndicator)process).scheduleRestart();
+      if (process != null) {
+        process.scheduleRestart();
         return;
       }
     }

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

@@ -317,11 +317,13 @@ public class LookupImpl extends LightweightHint implements Lookup, Disposable {
     ListScrollingUtil.ensureIndexIsVisible(myList, myList.getSelectedIndex(), 1);
   }
 
-  public boolean truncatePrefix() {
+  public boolean truncatePrefix(boolean preserveSelection) {
     final int len = myAdditionalPrefix.length();
     if (len == 0) return false;
 
-    markSelectionTouched();
+    if (preserveSelection) {
+      markSelectionTouched();
+    }
 
     myAdditionalPrefix = myAdditionalPrefix.substring(0, len - 1);
     myInitialPrefix = null;