[vcs-log] calculate hash lazily in loading details

platform/vcs-log/impl/src/com/intellij/vcs/log/data/AbstractDataGetter.java

@@ -1,6 +1,7 @@
 package com.intellij.vcs.log.data;
 
 import com.intellij.openapi.Disposable;
+import com.intellij.openapi.util.Computable;
 import com.intellij.openapi.util.Disposer;
 import com.intellij.openapi.vcs.VcsException;
 import com.intellij.openapi.vfs.VirtualFile;
@@ -9,6 +10,7 @@ import com.intellij.util.ThrowableConsumer;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.containers.MultiMap;
 import com.intellij.util.ui.UIUtil;
+import com.intellij.vcs.log.Hash;
 import com.intellij.vcs.log.VcsLogHashMap;
 import com.intellij.vcs.log.VcsLogProvider;
 import com.intellij.vcs.log.VcsShortCommitDetails;
@@ -132,9 +134,15 @@ abstract class AbstractDataGetter<T extends VcsShortCommitDetails> implements Di
 
       // fill the cache with temporary "Loading" values to avoid producing queries for each commit that has not been cached yet,
       // even if it will be loaded within a previous query
-      for (int commitId : hashes) {
+      for (final int commitId : hashes) {
         if (!myCache.isKeyCached(commitId)) {
-          myCache.put(commitId, (T)new LoadingDetails(myHashMap.getHash(commitId), taskNumber, root));
+          myCache.put(commitId, (T)new LoadingDetails(new Computable<Hash>(){
+
+            @Override
+            public Hash compute() {
+              return myHashMap.getHash(commitId);
+            }
+          }, taskNumber, root));
         }
       }
     }

platform/vcs-log/impl/src/com/intellij/vcs/log/data/LoadingDetails.java

@@ -1,5 +1,6 @@
 package com.intellij.vcs.log.data;
 
+import com.intellij.openapi.util.Computable;
 import com.intellij.openapi.util.ThrowableComputable;
 import com.intellij.openapi.vcs.changes.Change;
 import com.intellij.openapi.vfs.VirtualFile;
@@ -7,6 +8,7 @@ import com.intellij.vcs.log.Hash;
 import com.intellij.vcs.log.impl.VcsChangesLazilyParsedDetails;
 import com.intellij.vcs.log.impl.VcsUserImpl;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
 import java.util.Collections;
@@ -23,8 +25,8 @@ public class LoadingDetails extends VcsChangesLazilyParsedDetails {
 
   private final long myLoadingTaskIndex;
 
-  public LoadingDetails(@NotNull Hash hash, long loadingTaskIndex, @NotNull VirtualFile root) {
-    super(hash, Collections.<Hash>emptyList(), -1, root, "Loading...", STUB_USER, "", STUB_USER, -1,
+  public LoadingDetails(@NotNull Computable<Hash> computableHash, long loadingTaskIndex, @NotNull VirtualFile root) {
+    super(new LazyHash(computableHash), Collections.<Hash>emptyList(), -1, root, "Loading...", STUB_USER, "", STUB_USER, -1,
           new ThrowableComputable<Collection<Change>, Exception>() {
       @Override
       public Collection<Change> compute() throws Exception {
@@ -34,8 +36,37 @@ public class LoadingDetails extends VcsChangesLazilyParsedDetails {
     myLoadingTaskIndex = loadingTaskIndex;
   }
 
+
   public long getLoadingTaskIndex() {
     return myLoadingTaskIndex;
   }
 
+  private static class LazyHash implements Hash {
+    @NotNull
+    private final Computable<Hash> myComputableHash;
+    @Nullable
+    private volatile Hash myHash;
+
+    public LazyHash(@NotNull Computable<Hash> computableHash) {
+      myComputableHash = computableHash;
+    }
+
+    @NotNull
+    @Override
+    public String asString() {
+      if (myHash == null) {
+        myHash = myComputableHash.compute();
+      }
+      return myHash.asString();
+    }
+
+    @NotNull
+    @Override
+    public String toShortString() {
+      if (myHash == null) {
+        myHash = myComputableHash.compute();
+      }
+      return myHash.toShortString();
+    }
+  }
 }