Show the progress of an ongoing rebase (#74)

* Show rebase step number
* Show total number of steps

Author: tfpf

custom-prompt/custom-prompt.cc

@@ -198,6 +198,7 @@ class GitRepository
     void establish_description(void);
     void establish_tag(void);
     void establish_state(void);
+    void establish_state_rebasing(void);
     void establish_dirty_staged_untracked(void);
     // These are static methods because otherwise, their signatures do not
     // match the required signatures for use as callback functions.
@@ -310,7 +311,7 @@ void GitRepository::establish_state(void)
     case C::GIT_REPOSITORY_STATE_REBASE:
     case C::GIT_REPOSITORY_STATE_REBASE_INTERACTIVE:
     case C::GIT_REPOSITORY_STATE_REBASE_MERGE:
-        this->state = "rebasing";
+        this->establish_state_rebasing();
         break;
     case C::GIT_REPOSITORY_STATE_REVERT:
     case C::GIT_REPOSITORY_STATE_REVERT_SEQUENCE:
@@ -319,6 +320,30 @@ void GitRepository::establish_state(void)
     }
 }
 
+/**
+ * Obtain the rebase state of the working tree of the current Git repository.
+ */
+void GitRepository::establish_state_rebasing(void)
+{
+    this->state = "rebasing";
+    std::ifstream msgnum_file(this->gitdir / "rebase-merge/msgnum");
+    if (!msgnum_file.good())
+    {
+        return;
+    }
+    std::ifstream end_file(this->gitdir / "rebase-merge/end");
+    if (!end_file.good())
+    {
+        return;
+    }
+    std::string msgnum_contents, end_contents;
+    if (!(msgnum_file >> msgnum_contents) || !(end_file >> end_contents))
+    {
+        return;
+    }
+    this->state += ' ' + msgnum_contents + '/' + end_contents;
+}
+
 /**
  * Obtain the statuses of the index and working tree of the current Git
  * repository.