insert common prefix by default, but only for explicit completion (for now)

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

@@ -749,7 +749,7 @@ public class NormalCompletionTest extends LightFixtureCompletionTestCase {
     checkResultByFile(getTestName(false) + "_after.java")
   }
 
-  public void _testSecondInvocationToFillCommonPrefix() throws Throwable {
+  public void testSecondInvocationToFillCommonPrefix() throws Throwable {
     configure()
     type('a');
     complete();

platform/lang-impl/src/com/intellij/codeInsight/CodeInsightSettings.java

@@ -92,7 +92,7 @@ public class CodeInsightSettings implements PersistentStateComponent<Element>, C
   public boolean AUTOCOMPLETE_ON_CODE_COMPLETION = true;
   public boolean AUTOCOMPLETE_ON_SMART_TYPE_COMPLETION = true;
   public boolean AUTOCOMPLETE_ON_CLASS_NAME_COMPLETION = false;
-  public boolean AUTOCOMPLETE_COMMON_PREFIX = false;
+  public boolean AUTOCOMPLETE_COMMON_PREFIX = true;
   public boolean SHOW_STATIC_AFTER_INSTANCE = false;
 
   public boolean SHOW_FULL_SIGNATURES_IN_PARAMETER_INFO = false;

platform/lang-impl/src/com/intellij/codeInsight/completion/CodeCompletionHandlerBase.java

@@ -138,11 +138,9 @@ public class CodeCompletionHandlerBase implements CodeInsightActionHandler {
 
     CompletionPhase phase = CompletionServiceImpl.getCompletionPhase();
     boolean repeated = phase.indicator != null && phase.indicator.isRepeatedInvocation(myCompletionType, editor);
-    /*
     if (repeated && isAutocompleteCommonPrefixOnInvocation() && phase.fillInCommonPrefix()) {
       return;
     }
-    */
 
     if (invokedExplicitly) {
       time = phase.newCompletionStarted(time, repeated);

platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionPhase.java

@@ -185,6 +185,10 @@ public abstract class CompletionPhase implements Disposable {
 
     @Override
     public boolean fillInCommonPrefix() {
+      if (indicator.isAutopopupCompletion()) {
+        return false;
+      }
+
       return indicator.fillInCommonPrefix(true);
     }
   }