[git] IDEA-138787 Handle 'noop' situation: show a confirmation message

plugins/git4idea/src/git4idea/rebase/GitInteractiveRebaseEditorHandler.java

@@ -15,8 +15,10 @@
  */
 package git4idea.rebase;
 
+import com.intellij.CommonBundle;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.project.Project;
+import com.intellij.openapi.ui.Messages;
 import com.intellij.openapi.util.Ref;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.util.ui.UIUtil;
@@ -116,18 +118,32 @@ public class GitInteractiveRebaseEditorHandler implements Closeable, GitRebaseEd
             }
           }
           else {
-            GitInteractiveRebaseFile rebaseFile = new GitInteractiveRebaseFile(myProject, myRoot, path);
-            List<GitRebaseEntry> entries = rebaseFile.load();
             setRebaseEditorShown();
-            GitRebaseEditor editor = new GitRebaseEditor(myProject, myRoot, entries);
-            if (editor.showAndGet()) {
-              rebaseFile.save(editor.getEntries());
-              isSuccess.set(true);
-              return;
+            GitInteractiveRebaseFile rebaseFile = new GitInteractiveRebaseFile(myProject, myRoot, path);
+            try {
+              List<GitRebaseEntry> entries = rebaseFile.load();
+              GitRebaseEditor editor = new GitRebaseEditor(myProject, myRoot, entries);
+              if (editor.showAndGet()) {
+                rebaseFile.save(editor.getEntries());
+                isSuccess.set(true);
+                return;
+              }
+              else {
+                rebaseFile.cancel();
+                isSuccess.set(true);
+              }
             }
-            else {
-              rebaseFile.cancel();
-              isSuccess.set(true);
+            catch (GitInteractiveRebaseFile.NoopException e) {
+              LOG.info("Noop situation while rebasing " + myRoot);
+              String message = "There are no commits to rebase because the current branch is directly below the base branch " +
+                               "(the 'noop' situation).\n" +
+                               "Do you want to continue (this will reset the current branch to the base branch)?";
+              int rebase = Messages.showOkCancelDialog(myProject, message, "Git Rebase", CommonBundle.getOkButtonText(),
+                                                       CommonBundle.getCancelButtonText(), Messages.getQuestionIcon());
+              if (rebase == Messages.OK) {
+                isSuccess.set(true);
+                return;
+              }
             }
           }
         }

plugins/git4idea/src/git4idea/rebase/GitInteractiveRebaseFile.java

@@ -42,12 +42,18 @@ class GitInteractiveRebaseFile {
   }
 
   @NotNull
-  public List<GitRebaseEntry> load() throws IOException {
+  public List<GitRebaseEntry> load() throws IOException, NoopException {
     String encoding = GitConfigUtil.getLogEncoding(myProject, myRoot);
     List<GitRebaseEntry> entries = ContainerUtil.newArrayList();
     final StringScanner s = new StringScanner(FileUtil.loadFile(new File(myFile), encoding));
+    boolean noop = false;
     while (s.hasMoreData()) {
-      if (s.isEol() || s.startsWith('#') || s.startsWith("noop")) {
+      if (s.isEol() || s.startsWith('#')) {
+        s.nextLine();
+        continue;
+      }
+      if (s.startsWith("noop")) {
+        noop = true;
         s.nextLine();
         continue;
       }
@@ -57,6 +63,9 @@ class GitInteractiveRebaseFile {
 
       entries.add(new GitRebaseEntry(action, hash, comment));
     }
+    if (noop && entries.isEmpty()) {
+      throw new NoopException();
+    }
     return entries;
   }
 
@@ -93,4 +102,7 @@ class GitInteractiveRebaseFile {
     }
     return file;
   }
+
+  static class NoopException extends Exception {
+  }
 }