don't be smart, just calculate the common prefix based on lookup strings and insert it (IDEA-63646,IDEA-70503)

java/java-tests/testData/codeInsight/completion/normal/SaxParserCommonPrefix.java

@@ -0,0 +1,5 @@
+class Bar {
+  {
+    SaxP<caret>
+  }
+}

java/java-tests/testData/codeInsight/completion/normal/SaxParserCommonPrefix_after.java

@@ -0,0 +1,5 @@
+class Bar {
+  {
+    SAXParse<caret>
+  }
+}

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

@@ -958,6 +958,12 @@ public class NormalCompletionTest extends LightFixtureCompletionTestCase {
 
   public void testStaticInnerExtendingOuter() throws Exception { doTest() }
 
+  public void testSaxParserCommonPrefix() throws Exception {
+    myFixture.addClass("package foo.bar; public class SAXParser {}")
+    myFixture.addClass("package foo.bar.goo; public class SAXParseException {}")
+    doTest()
+  }
+
   public void testNewClassAngleBracket() throws Exception { doTest('<') }
   public void testNewClassSquareBracket() throws Exception { doTest('[') }
 

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

@@ -1032,15 +1032,6 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
     }
   }
 
-  private static int divideString(String lookupString, PrefixMatcher matcher) {
-    for (int i = matcher.getPrefix().length(); i <= lookupString.length(); i++) {
-      if (matcher.prefixMatches(lookupString.substring(0, i))) {
-        return i;
-      }
-    }
-    return -1;
-  }
-
   public boolean fillInCommonPrefix(boolean explicitlyInvoked) {
     if (explicitlyInvoked) {
       setFocused(true);
@@ -1060,37 +1051,39 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
     final PrefixMatcher firstItemMatcher = itemMatcher(firstItem);
     final String oldPrefix = firstItemMatcher.getPrefix();
     final String presentPrefix = oldPrefix + myAdditionalPrefix;
-    final PrefixMatcher matcher = firstItemMatcher.cloneWithPrefix(presentPrefix);
-    String lookupString = firstItem.getLookupString();
-    int div = divideString(lookupString, matcher);
-    if (div < 0) return false;
-
-    String beforeCaret = lookupString.substring(0, div);
-    String afterCaret = lookupString.substring(div);
-
+    String commonPrefix = firstItem.getLookupString();
 
     for (int i = 1; i < listModel.getSize(); i++) {
       LookupElement item = (LookupElement)listModel.getElementAt(i);
       if (!oldPrefix.equals(itemMatcher(item).getPrefix())) return false;
 
-      lookupString = item.getLookupString();
-      div = divideString(lookupString, itemMatcher(item).cloneWithPrefix(presentPrefix));
-      if (div < 0) return false;
-
-      String _afterCaret = lookupString.substring(div);
-      if (beforeCaret != null) {
-        if (div != beforeCaret.length() || !lookupString.startsWith(beforeCaret)) {
-          beforeCaret = null;
-        }
+      final String lookupString = item.getLookupString();
+      final int length = Math.min(commonPrefix.length(), lookupString.length());
+      if (length < commonPrefix.length()) {
+        commonPrefix = commonPrefix.substring(0, length);
       }
 
-      while (afterCaret.length() > 0) {
-        if (_afterCaret.startsWith(afterCaret)) {
+      for (int j = 0; j < length; j++) {
+        if (commonPrefix.charAt(j) != lookupString.charAt(j)) {
+          commonPrefix = lookupString.substring(0, j);
           break;
         }
-        afterCaret = afterCaret.substring(0, afterCaret.length() - 1);
       }
-      if (afterCaret.length() == 0) return false;
+
+      if (commonPrefix.length() == 0 || commonPrefix.length() < presentPrefix.length()) {
+        return false;
+      }
+    }
+
+    if (commonPrefix.equals(presentPrefix)) {
+      return false;
+    }
+
+    for (int i = 0; i < listModel.getSize(); i++) {
+      LookupElement item = (LookupElement)listModel.getElementAt(i);
+      if (!itemMatcher(item).cloneWithPrefix(commonPrefix).prefixMatches(item)) {
+        return false;
+      }
     }
 
     if (myAdditionalPrefix.length() == 0 && myInitialPrefix == null && !explicitlyInvoked) {
@@ -1100,31 +1093,21 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
       myInitialPrefix = null;
     }
 
-    final String finalBeforeCaret = beforeCaret;
-    final String finalAfterCaret = afterCaret;
+    final String finalCommonPrefix = commonPrefix;
     Runnable runnable = new Runnable() {
       public void run() {
-        doInsertCommonPrefix(presentPrefix, finalBeforeCaret, finalAfterCaret);
+        doInsertCommonPrefix(presentPrefix, finalCommonPrefix);
       }
     };
     performGuardedChange(runnable);
     return true;
   }
 
-  private void doInsertCommonPrefix(String presentPrefix, String beforeCaret, String afterCaret) {
+  private void doInsertCommonPrefix(String presentPrefix, String newPrefix) {
     EditorModificationUtil.deleteSelectedText(myEditor);
     int offset = myEditor.getCaretModel().getOffset();
-    if (beforeCaret != null) { // correct case, expand camel-humps
-      final int start = offset - presentPrefix.length();
-      myAdditionalPrefix = "";
-      myEditor.getDocument().replaceString(start, offset, beforeCaret);
-      presentPrefix = beforeCaret;
-    }
-
-    offset = myEditor.getCaretModel().getOffset();
-    myEditor.getDocument().insertString(offset, afterCaret);
-
-    final String newPrefix = presentPrefix + afterCaret;
+    final int start = offset - presentPrefix.length();
+    myEditor.getDocument().replaceString(start, offset, newPrefix);
 
     Map<LookupElement, PrefixMatcher> newItems = myModel.retainMatchingItems(newPrefix, this);
     myMatchers.clear();
@@ -1132,8 +1115,7 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable
 
     myAdditionalPrefix = "";
 
-    offset += afterCaret.length();
-    myEditor.getCaretModel().moveToOffset(offset);
+    myEditor.getCaretModel().moveToOffset(start + newPrefix.length());
     refreshUi();
   }
 

plugins/android/testData/dom/layout/commonPrefixIdea63531_after.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android">
-    <ImageView android:layout_<caret>
+    <ImageView android:lay<caret>
 </LinearLayout>
 

plugins/android/testSrc/org/jetbrains/android/dom/AndroidLayoutDomTest.java

@@ -53,9 +53,9 @@ public class AndroidLayoutDomTest extends AndroidDomTest {
     toTestCompletion("an5.xml", "an5_after.xml");
   }
 
-  /*public void testCommonPrefixIdea63531() throws Throwable {
+  public void testCommonPrefixIdea63531() throws Throwable {
     toTestCompletion("commonPrefixIdea63531.xml", "commonPrefixIdea63531_after.xml");
-  }*/
+  }
 
   public void testHighlighting() throws Throwable {
     doTestHighlighting("hl.xml");