index: add a dirty bit reflecting unsaved changes

Teach the index when it is "dirty", and has unsaved changes.  Consider
the index dirty whenever a caller has added or removed an entry from the
main index, REUC or NAME section, including when the index is completely
cleared.  Similarly, consider the index _not_ dirty immediately after it
is written, or when it is read from the on-disk index.

This allows us to ensure that unsaved changes are not lost when we
automatically refresh the index.

src/index.c

@@ -516,6 +516,8 @@ static int index_remove_entry(git_index *index, size_t pos)
 		} else {
 			index_entry_free(entry);
 		}
+
+		index->dirty = 1;
 	}
 
 	return error;
@@ -527,6 +529,7 @@ int git_index_clear(git_index *index)
 
 	assert(index);
 
+	index->dirty = 1;
 	index->tree = NULL;
 	git_pool_clear(&index->tree_pool);
 
@@ -637,8 +640,10 @@ int git_index_read(git_index *index, int force)
 	index->on_disk = git_path_exists(index->index_file_path);
 
 	if (!index->on_disk) {
-		if (force)
-			return git_index_clear(index);
+		if (force && (error = git_index_clear(index)) < 0)
+			return error;
+
+		index->dirty = 0;
 		return 0;
 	}
 
@@ -650,6 +655,7 @@ int git_index_read(git_index *index, int force)
 			index->index_file_path);
 		return updated;
 	}
+
 	if (!updated && !force)
 		return 0;
 
@@ -665,8 +671,10 @@ int git_index_read(git_index *index, int force)
 	if (!error)
 		error = parse_index(index, buffer.ptr, buffer.size);
 
-	if (!error)
+	if (!error) {
 		git_futils_filestamp_set(&index->stamp, &stamp);
+		index->dirty = 0;
+	}
 
 	git_buf_dispose(&buffer);
 	return error;
@@ -735,8 +743,10 @@ static int truncate_racily_clean(git_index *index)
 		/* Ensure that we have a stage 0 for this file (ie, it's not a
 		 * conflict), otherwise smudging it is quite pointless.
 		 */
-		if (entry)
+		if (entry) {
 			entry->file_size = 0;
+			index->dirty = 1;
+		}
 	}
 
 done:
@@ -774,8 +784,9 @@ int git_index_write(git_index *index)
 
 	truncate_racily_clean(index);
 
-	if ((error = git_indexwriter_init(&writer, index)) == 0)
-		error = git_indexwriter_commit(&writer);
+	if ((error = git_indexwriter_init(&writer, index)) == 0 &&
+		(error = git_indexwriter_commit(&writer)) == 0)
+		index->dirty = 0;
 
 	git_indexwriter_cleanup(&writer);
 
@@ -1389,6 +1400,8 @@ static int index_insert(
 	if (error < 0) {
 		index_entry_free(*entry_ptr);
 		*entry_ptr = NULL;
+	} else {
+		index->dirty = 1;
 	}
 
 	return error;
@@ -1616,6 +1629,8 @@ int git_index__fill(git_index *index, const git_vector *source_entries)
 		INSERT_IN_MAP(index, entry, &ret);
 		if (ret < 0)
 			break;
+
+		index->dirty = 1;
 	}
 
 	if (!ret)
@@ -2053,6 +2068,7 @@ int git_index_name_add(git_index *index,
 		return -1;
 	}
 
+	index->dirty = 1;
 	return 0;
 }
 
@@ -2067,6 +2083,8 @@ void git_index_name_clear(git_index *index)
 		index_name_entry_free(conflict_name);
 
 	git_vector_clear(&index->names);
+
+	index->dirty = 1;
 }
 
 size_t git_index_reuc_entrycount(git_index *index)
@@ -2092,6 +2110,8 @@ static int index_reuc_insert(
 	assert(git_vector_is_sorted(&index->reuc));
 
 	res = git_vector_insert_sorted(&index->reuc, reuc, &index_reuc_on_dup);
+	index->dirty = 1;
+
 	return res == GIT_EEXISTS ? 0 : res;
 }
 
@@ -2157,6 +2177,7 @@ int git_index_reuc_remove(git_index *index, size_t position)
 	if (!error)
 		index_entry_reuc_free(reuc);
 
+	index->dirty = 1;
 	return error;
 }
 
@@ -2170,6 +2191,8 @@ void git_index_reuc_clear(git_index *index)
 		index_entry_reuc_free(git__swap(index->reuc.contents[i], NULL));
 
 	git_vector_clear(&index->reuc);
+
+	index->dirty = 1;
 }
 
 static int index_error_invalid(const char *message)
@@ -2604,6 +2627,7 @@ static int parse_index(git_index *index, const char *buffer, size_t buffer_size)
 	git_vector_set_sorted(&index->entries, !index->ignore_case);
 	git_vector_sort(&index->entries);
 
+	index->dirty = 0;
 done:
 	return error;
 }
@@ -3070,6 +3094,8 @@ int git_index_read_tree(git_index *index, const git_tree *tree)
 		entries_map = git__swap(index->entries_map, entries_map);
 	}
 
+	index->dirty = 1;
+
 cleanup:
 	git_vector_free(&entries);
 	git_idxmap_free(entries_map);
@@ -3209,6 +3235,7 @@ static int git_index_read_iterator(
 
 	clear_uptodate(index);
 
+	index->dirty = 1;
 	error = 0;
 
 done:
@@ -3601,6 +3628,7 @@ int git_indexwriter_commit(git_indexwriter *writer)
 		return -1;
 	}
 
+	writer->index->dirty = 0;
 	writer->index->on_disk = 1;
 	git_oid_cpy(&writer->index->checksum, &checksum);
 

src/index.h

@@ -37,6 +37,7 @@ struct git_index {
 	unsigned int ignore_case:1;
 	unsigned int distrust_filemode:1;
 	unsigned int no_symlinks:1;
+	unsigned int dirty:1;	/* whether we have unsaved changes */
 
 	git_tree_cache *tree;
 	git_pool tree_pool;
@@ -143,6 +144,11 @@ extern int git_index_snapshot_find(
 /* Replace an index with a new index */
 int git_index_read_index(git_index *index, const git_index *new_index);
 
+GIT_INLINE(int) git_index_is_dirty(git_index *index)
+{
+	return index->dirty;
+}
+
 typedef struct {
 	git_index *index;
 	git_filebuf file;