[git] Fix parsing error when empty logs are read from a repository

Fixes #17

perceval/backends/git.py

@@ -296,6 +296,10 @@ class GitParser:
 
     The commit ends with an empty line.
 
+    Take into account that one empty line is valid at the beginning
+    of the log. This allows to parse empty logs without raising
+    exceptions.
+
     This example was generated using the next command:
 
         git log --raw --numstat --pretty=fuller --decorate=full \
@@ -332,21 +336,23 @@ class GitParser:
     GIT_NEXT_STATE_REGEXP = re.compile(EMPTY_LINE_PATTERN, re.VERBOSE)
 
     # Git parser status
-    (COMMIT,
+    (INIT,
+     COMMIT,
      HEADER,
      MESSAGE,
-     FILE) = range(4)
+     FILE) = range(5)
 
     def __init__(self, stream):
         self.stream = stream
         self.nline = 0
-        self.state = self.COMMIT
+        self.state = self.INIT
 
         # Aux vars to store the commit that is being parsed
         self.commit = None
         self.commit_files = {}
 
         self.handlers = {
+            self.INIT : self._handle_init,
             self.COMMIT : self._handle_commit,
             self.HEADER : self._handle_header,
             self.MESSAGE : self._handle_message,
@@ -364,7 +370,7 @@ def parse(self):
             while not parsed:
                 parsed = self.handlers[self.state](line)
 
-                if self.state == self.COMMIT:
+                if self.state == self.COMMIT and self.commit:
                     commit = self._build_commit()
                     logger.debug("Commit %s parsed", commit['commit'])
                     yield commit
@@ -389,6 +395,17 @@ def remove_none_values(d):
 
         return commit
 
+    def _handle_init(self, line):
+        m = self.GIT_NEXT_STATE_REGEXP.match(line)
+
+        # In both cases, the parser advances to the next state.
+        # It only has to check whether the line has to be parsed
+        # again or not
+        self.state = self.COMMIT
+        parsed = m is not None
+
+        return parsed
+
     def _handle_commit(self, line):
         m = self.GIT_COMMIT_REGEXP.match(line)
         if not m:

tests/data/git_log_empty.txt

@@ -0,0 +1 @@
+

tests/test_git.py

@@ -130,6 +130,17 @@ def test_fetch_since_date(self):
 
         shutil.rmtree(new_path)
 
+    def test_fetch_empty_log(self):
+        """Test whether it parsers an empty log"""
+
+        new_path = os.path.join(self.tmp_path, 'newgit')
+
+        from_date = datetime.datetime(2020, 1, 1, 1, 1, 1)
+        git = Git(self.git_path, new_path)
+        commits = [commit for commit in git.fetch(from_date=from_date)]
+
+        self.assertListEqual(commits, [])
+
     def test_fetch_from_file(self):
         """Test whether commits are fetched from a Git log file"""
 
@@ -282,6 +293,15 @@ def test_parser(self):
                     }
         self.assertDictEqual(commits[5], expected)
 
+    def test_parser_empty_log(self):
+        """Test if it parsers an empty git log stream"""
+
+        with open("data/git_log_empty.txt", 'r') as f:
+            parser = GitParser(f)
+            commits = [commit for commit in parser.parse()]
+
+        self.assertListEqual(commits, [])
+
     def test_commit_pattern(self):
         """Test commit pattern"""
 
@@ -548,6 +568,19 @@ def test_log_from_date(self):
 
         shutil.rmtree(new_path)
 
+    def test_log_empty(self):
+        """Test if an empty line is returned when the log is empty"""
+
+        new_path = os.path.join(self.tmp_path, 'newgit')
+
+        repo = GitRepository.clone(self.git_path, new_path)
+        gitlog = repo.log(from_date=datetime.datetime(2020, 1, 1, 1, 1, 1))
+        gitlog = [line for line in gitlog]
+
+        self.assertListEqual(gitlog, [''])
+
+        shutil.rmtree(new_path)
+
 
 if __name__ == "__main__":
     unittest.main()