rebase: identify a rebase that has not started

In `git_rebase_operation_current()`, indicate when a rebase has not
started (with `GIT_REBASE_NO_OPERATION`) rather than conflating that
with the first operation being in-progress.

CHANGELOG.md

@@ -101,6 +101,10 @@ v0.22 + 1
 * `git_note_default_ref()` now uses a `git_buf` to return the string,
   as the string is otherwise not guaranteed to stay allocated.
 
+* `git_rebase_operation_current()` will return `GIT_REBASE_NO_OPERATION`
+  if it is called immediately after creating a rebase session but before
+  you have applied the first patch.
+
 v0.22
 ------
 

include/git2/rebase.h

@@ -89,6 +89,9 @@ typedef enum {
 #define GIT_REBASE_OPTIONS_VERSION 1
 #define GIT_REBASE_OPTIONS_INIT {GIT_REBASE_OPTIONS_VERSION}
 
+/** Indicates that a rebase operation is not (yet) in progress. */
+#define GIT_REBASE_NO_OPERATION SIZE_MAX
+
 /**
  * A rebase operation
  *
@@ -170,6 +173,9 @@ GIT_EXTERN(size_t) git_rebase_operation_entrycount(git_rebase *rebase);
 
 /**
  * Gets the index of the rebase operation that is currently being applied.
+ * If the first operation has not yet been applied (because you have
+ * called `init` but not yet `next`) then this returns
+ * `GIT_REBASE_NO_OPERATION`.
  *
  * @param rebase The in-progress rebase
  * @return The index of the rebase operation currently being applied.

src/rebase.c

@@ -1148,7 +1148,7 @@ size_t git_rebase_operation_current(git_rebase *rebase)
 {
 	assert(rebase);
 
-	return rebase->current;
+	return rebase->started ? rebase->current : GIT_REBASE_NO_OPERATION;
 }
 
 git_rebase_operation *git_rebase_operation_byindex(git_rebase *rebase, size_t idx)

tests/rebase/iterator.c

@@ -65,7 +65,7 @@ void test_rebase_iterator__iterates(void)
 	cl_git_pass(git_annotated_commit_from_ref(&upstream_head, repo, upstream_ref));
 
 	cl_git_pass(git_rebase_init(&rebase, repo, branch_head, upstream_head, NULL, NULL));
-	test_operations(rebase, 0);
+	test_operations(rebase, GIT_REBASE_NO_OPERATION);
 	git_rebase_free(rebase);
 
 	cl_git_pass(git_rebase_open(&rebase, repo));