Try to auto-detect revision in append mode if not specified

gitdch

@@ -10,6 +10,7 @@ import sys
 import textwrap
 
 import git
+from git.exc import GitCommandError
 
 VERSION = '0.0'
 DEFAULT_GIT_PATCH = './'
@@ -227,14 +228,6 @@ if not options.quiet or not options.logfile:
 
 repo = git.Repo(options.git_path)
 
-log.info('Generate changelog from git commits')
-
-versions = []
-tag_commits = dict(
-    (tag.commit.binsha, tag)
-    for tag in repo.tags
-)
-
 
 def clean_deb_version(version_name):
     """ Clean debian version name """
@@ -246,6 +239,45 @@ def clean_deb_version(version_name):
     return version_name
 
 
+if not options.version:
+    log.info('Detect current version from git tags & commits')
+    options.version = clean_deb_version(
+        repo.git.describe('--always', '--tags')
+    )
+    log.info('Currrent version detected: %s', options.version)
+
+if options.output and options.append and not options.revision:
+    log.info(
+        'Append mode enabled but no revision specify, try to detect it from '
+        'last modification of the changelog file')
+    try:
+        last_change_commit = next(repo.iter_commits(paths=options.output))
+        # pylint: disable=consider-using-f-string
+        options.revision = '{0}..HEAD'.format(last_change_commit)
+        log.info(
+            'Last change commit of the output file is "%s": use revision "%s"',
+            last_change_commit, options.revision)
+    except StopIteration:
+        log.warning(
+            'Fail to auto-detect last change commit of changelog file: it '
+            'seem not tracked. Continue without revision.')
+    except GitCommandError:
+        log.warning(
+            "Fail to auto-detect last change commit of changelog file. May "
+            "be it's outside of the git repository. Continue without "
+            "revision.")
+        # Reset repo object of to avoid BrokenPipeError
+        repo = git.Repo(options.git_path)
+
+log.info('Generate changelog from git commits')
+
+versions = []
+tag_commits = dict(
+    (tag.commit.binsha, tag)
+    for tag in repo.tags
+)
+
+
 def add_version():
     """ Add version info """
     global messages  # pylint: disable=global-statement
@@ -264,12 +296,7 @@ def add_version():
 
 tag = None
 version_commit = None
-version = (
+version = options.version
-    options.version or
-    clean_deb_version(
-        repo.git.describe('--always', '--tags')
-    )
-)
 messages = []
 for commit in repo.iter_commits(rev=options.revision):
     log.debug('Commit %s (%s)', commit, commit.summary)
@@ -350,10 +377,15 @@ else:
 if options.release_notes:
     log.info('Generate Markdown release notes')
     release_notes_lines = ['# Changelog:\n\n']
+    if versions:
         release_notes_lines.extend([
             '* {0}\n'.format(message)
             for message in versions[0]['messages']
         ])
+    else:
+        release_notes_lines.extend([
+            '* Release version {0}\n'.format(options.version)
+        ])
     log.info(
         'Write generated Markdown release notes in file %s',
         options.release_notes)