vcs: Show History for Selection - more consistent Block logic

greedy expand range on damage

platform/platform-tests/testSrc/com/intellij/diff/SelectedBlockHistoryTest.java

@@ -182,6 +182,17 @@ public class SelectedBlockHistoryTest extends TestCase {
     );
   }
 
+  public void test15() throws FilesTooBigForDiffException {
+    doTest(
+      new String[]{"1"},
+      new String[]{"0"},
+      new String[]{"3"},
+
+      new String[]{"1", "4"},
+      new String[]{"5", "0"},
+      new String[]{"3"}
+    );
+  }
 
   public void testContent(){
     Block block = new Block("0\n1\n2\n3\n4\n5\n6", 3, 7);

platform/vcs-impl/src/com/intellij/diff/Block.java

@@ -46,8 +46,9 @@ public class Block {
 
   @NotNull
   public Block createPreviousBlock(@NotNull String[] prevContent) {
-    int startLine = myStart;
+    int start = -1;
-    int endLine = myEnd;
+    int end = -1;
+    int shift = 0;
 
     Diff.Change change = Diff.buildChangesSomehow(prevContent, getSource());
     while (change != null) {
@@ -56,31 +57,21 @@ public class Block {
       int endLine1 = startLine1 + change.deleted;
       int endLine2 = startLine2 + change.inserted;
 
-      int shiftStart = startLine2 - startLine1;
+      if (Math.max(myStart, startLine2) < Math.min(myEnd, endLine2)) {
-      int shiftEnd = endLine2 - endLine1;
+        // ranges intersect
-
+        if (startLine2 <= myStart) start = startLine1;
-      if (startLine2 <= myStart) {
+        if (endLine2 > myEnd) end = endLine1;
-        startLine = myStart - shiftStart;
-      }
-
-      if (endLine2 <= myStart) {
-        startLine = myStart - shiftEnd;
-      }
-
-      if (startLine2 < myEnd) {
-        endLine = myEnd - shiftEnd;
       }
+      if (start == -1 && startLine2 > myStart) start = myStart - shift;
+      if (end == -1 && startLine2 >= myEnd) end = myEnd - shift;
 
+      shift += change.inserted - change.deleted;
       change = change.link;
     }
+    if (start == -1) start = myStart - shift;
+    if (end == -1) end = myEnd - shift;
 
-    if (endLine > prevContent.length) {
+    return new Block(prevContent, start, end);
-      endLine = prevContent.length;
-    }
-    if (startLine < 0) startLine = 0;
-    if (endLine < startLine) endLine = startLine;
-
-    return new Block(prevContent, startLine, endLine);
   }
 
   @NotNull