Git error handling:

1. Check GitExecutableValidator in GitChangeProvider and GitHistoryProvider.
2. Stop "loading history" indicator if process failed to start in GitHistoryUtils. Allows to have several attempts - had to restart IDEA to reinvoke history before that.

plugins/git4idea/src/git4idea/changes/GitChangeProvider.java

@@ -26,6 +26,7 @@ import git4idea.GitContentRevision;
 import git4idea.GitRevisionNumber;
 import git4idea.GitUtil;
 import git4idea.GitVcs;
+import git4idea.config.GitExecutableValidator;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Collection;
@@ -63,20 +64,23 @@ public class GitChangeProvider implements ChangeProvider {
     }
     Collection<VirtualFile> roots = GitUtil.gitRootsForPaths(affected);
 
-    final MyNonChangedHolder holder = new MyNonChangedHolder(myProject, dirtyScope.getDirtyFilesNoExpand(), addGate);
-
-    for (VirtualFile root : roots) {
-      ChangeCollector c = new ChangeCollector(myProject, dirtyScope, root);
-      final Collection<Change> changes = c.changes();
-      holder.changed(changes);
-      for (Change file : changes) {
-        builder.processChange(file, GitVcs.getKey());
+    try {
+      final MyNonChangedHolder holder = new MyNonChangedHolder(myProject, dirtyScope.getDirtyFilesNoExpand(), addGate);
+      for (VirtualFile root : roots) {
+        ChangeCollector c = new ChangeCollector(myProject, dirtyScope, root);
+        final Collection<Change> changes = c.changes();
+        holder.changed(changes);
+        for (Change file : changes) {
+          builder.processChange(file, GitVcs.getKey());
+        }
+        for (VirtualFile f : c.unversioned()) {
+          builder.processUnversionedFile(f);
+          holder.unversioned(f);
+        }
+        holder.feedBuilder(builder);
       }
-      for (VirtualFile f : c.unversioned()) {
-        builder.processUnversionedFile(f);
-        holder.unversioned(f);
-      }
-      holder.feedBuilder(builder);
+    } catch (VcsException e) {// most probably the error happened because git is not configured
+      GitExecutableValidator.getInstance(myProject).showNotificationOrThrow(e);
     }
   }
 

plugins/git4idea/src/git4idea/config/GitExecutableValidator.java

@@ -19,11 +19,14 @@ import com.intellij.notification.Notification;
 import com.intellij.notification.NotificationListener;
 import com.intellij.notification.NotificationType;
 import com.intellij.notification.Notifications;
+import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.components.ServiceManager;
 import com.intellij.openapi.options.ShowSettingsUtil;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.ui.Messages;
 import com.intellij.openapi.vcs.VcsException;
+import com.intellij.ui.GuiUtils;
+import com.intellij.util.ui.UIUtil;
 import git4idea.GitVcs;
 import git4idea.i18n.GitBundle;
 import org.jetbrains.annotations.NotNull;
@@ -65,10 +68,7 @@ public class GitExecutableValidator {
    * Expires the notification if user fixes the path to Git from the opened Settings dialog.
    */
   public void showExecutableNotConfiguredNotification() {
-    if (myNotification != null && !myNotification.isExpired()) { // don't display this notification twice
-      return;
-    }
-    myNotification = new Notification(GitVcs.NOTIFICATION_GROUP_ID, GitBundle.getString("executable.error.title"), 
+    final Notification newNotification = new Notification(GitVcs.NOTIFICATION_GROUP_ID, GitBundle.getString("executable.error.title"),
       GitBundle.getString("executable.error.description"), NotificationType.ERROR,
       new NotificationListener() {
         public void hyperlinkUpdate(@NotNull Notification notification, @NotNull HyperlinkEvent event) {
@@ -78,7 +78,19 @@ public class GitExecutableValidator {
           }
         }
       });
-    Notifications.Bus.notify(myNotification, myProject);
+
+    // expire() needs to be called from EventDispatch thread. notify handles it by itself.
+    // but we want to be sure that previous notification expires before new one is shown (and assigned to myNotification).
+    UIUtil.invokeLaterIfNeeded(new Runnable() {
+      @Override public void run() {
+        if (myNotification != null && !myNotification.isExpired()) {
+          // don't display this notification twice, but better to redisplay it again so that popup appears.
+          myNotification.expire();
+        }
+        myNotification = newNotification;
+        Notifications.Bus.notify(myNotification, myProject);
+      }
+    });
   }
 
   /**
@@ -89,5 +101,20 @@ public class GitExecutableValidator {
       showExecutableNotConfiguredNotification();
     }
   }
+
+  /**
+   * Checks if git executable is valid. If not (which is a common case for low-level vcs exceptions), shows the
+   * notification. Otherwise throws the exception.
+   * This is to be used in catch-clauses
+   * @param e exception which was thrown.
+   * @throws VcsException if git executable is valid.
+   */
+  public void showNotificationOrThrow(VcsException e) throws VcsException {
+    if (!isGitExecutableValid()) {
+      showExecutableNotConfiguredNotification();
+    } else {
+      throw e;
+    }
+  }
   
 }

plugins/git4idea/src/git4idea/history/GitHistoryProvider.java

@@ -25,6 +25,7 @@ import com.intellij.util.Consumer;
 import com.intellij.util.ui.ColumnInfo;
 import git4idea.GitFileRevision;
 import git4idea.actions.GitShowAllSubmittedFilesAction;
+import git4idea.config.GitExecutableValidator;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -43,7 +44,7 @@ public class GitHistoryProvider implements VcsHistoryProvider {
   /**
    * the current project instance
    */
-  private final Project project;
+  private final Project myProject;
 
   /**
    * A constructor
@@ -51,7 +52,7 @@ public class GitHistoryProvider implements VcsHistoryProvider {
    * @param project a context project
    */
   public GitHistoryProvider(@NotNull Project project) {
-    this.project = project;
+    this.myProject = project;
   }
 
   /**
@@ -89,7 +90,12 @@ public class GitHistoryProvider implements VcsHistoryProvider {
    */
   @Nullable
   public VcsHistorySession createSessionFor(final FilePath filePath) throws VcsException {
-    List<VcsFileRevision> revisions = GitHistoryUtils.history(project, filePath);
+    List<VcsFileRevision> revisions = null;
+    try {
+      revisions = GitHistoryUtils.history(myProject, filePath);
+    } catch (VcsException e) {
+      GitExecutableValidator.getInstance(myProject).showNotificationOrThrow(e);
+    }
     return createSession(filePath, revisions);
   }
 
@@ -98,7 +104,7 @@ public class GitHistoryProvider implements VcsHistoryProvider {
       @Nullable
       protected VcsRevisionNumber calcCurrentRevisionNumber() {
         try {
-          return GitHistoryUtils.getCurrentRevision(project, GitHistoryUtils.getLastCommitName(project, filePath));
+          return GitHistoryUtils.getCurrentRevision(myProject, GitHistoryUtils.getLastCommitName(myProject, filePath));
         }
         catch (VcsException e) {
           // likely the file is not under VCS anymore.
@@ -123,13 +129,18 @@ public class GitHistoryProvider implements VcsHistoryProvider {
   public void reportAppendableHistory(final FilePath path, final VcsAppendableHistorySessionPartner partner) throws VcsException {
     final VcsAbstractHistorySession emptySession = createSession(path, Collections.<VcsFileRevision>emptyList());
     partner.reportCreatedEmptySession(emptySession);
-    GitHistoryUtils.history(project, path, new Consumer<GitFileRevision>() {
+    final GitExecutableValidator validator = GitExecutableValidator.getInstance(myProject);
+    GitHistoryUtils.history(myProject, path, new Consumer<GitFileRevision>() {
       public void consume(GitFileRevision gitFileRevision) {
         partner.acceptRevision(gitFileRevision);
       }
     }, new Consumer<VcsException>() {
       public void consume(VcsException e) {
-        partner.reportException(e);
+        if (!validator.isGitExecutableValid()) {
+          validator.showExecutableNotConfiguredNotification();
+        } else {
+          partner.reportException(e);
+        }
       }
     });
   }

plugins/git4idea/src/git4idea/history/GitHistoryUtils.java

@@ -166,6 +166,7 @@ public class GitHistoryUtils {
       public void startFailed(Throwable exception) {
         //noinspection ThrowableInstanceNeverThrown
         exceptionConsumer.consume(new VcsException(exception));
+        semaphore.up();
       }
 
       @Override