repo: diff: add option to show "creation event" diff for root commit

At its inception, Git did not show a "creation event" diff for a
project's root commit since early projects, such as the Linux kernel,
were already well established, and a large root diff was considered
uninteresting noise.

On the other hand, new projects adopting Git typically have small root
commits, and such a "creation event" is likely to have meaning, rather
than being pure noise. Consequently, git-diff-tree gained a --root flag
in dc26bd89 (diff-tree: add "--root" flag to show a root commit as a big
creation event, 2005-05-19), though it was disabled by default.

Displaying the root "creation event" diff, however, became the default
behavior when configuration option 'log.showroot' was added to git-log
in 0f03ca94 (config option log.showroot to show the diff of root
commits; 2006-11-23). And, gitk (belatedly) followed suit when it
learned to respect 'log.showroot' in b2b76d10 (gitk: Teach gitk to
respect log.showroot; 2011-10-04).

By default, these tools now all show the root diff as a "creation
event", however, git-arr suppresses it unconditionally. Resolve this
shortcoming by adding a new git-arr configuration option "rootdiff" to
control the behavior (enabled by default).

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Alberto Bertogli <albertito@blitiri.com.ar>

3 files changed, 13 insertions, 2 deletions

diff --git a/git-arr b/git-arr
index 902bb89..95455ec 100755
--- a/git-arr
+++ b/git-arr
@@ -46,6 +46,7 @@ def load_config(path):
     """
     defaults = {
         'tree': 'yes',
+        'rootdiff': 'yes',
         'desc': '',
         'recursive': 'no',
         'commits_in_summary': '10',
@@ -108,6 +109,7 @@ def load_config(path):
         if r.info.max_pages <= 0:
             r.info.max_pages = sys.maxint
         r.info.generate_tree = config.getboolean(s, 'tree')
+        r.info.root_diff = config.getboolean(s, 'rootdiff')
 
         r.info.web_url = config.get(s, 'web_url')
         web_url_file = fullpath + '/' + config.get(s, 'web_url_file')
diff --git a/git.py b/git.py
index bddca70..9a77c7c 100644
--- a/git.py
+++ b/git.py
@@ -198,8 +198,6 @@ class Repo:
     def __init__(self, path, branch = None, name = None, info = None):
         self.path = path
         self.branch = branch
-
-        # We don't need these, but provide them for the users' convenience.
         self.name = name
         self.info = info or SimpleNamespace()
 
@@ -303,6 +301,8 @@ class Repo:
         cmd.patch = None
         cmd.numstat = None
         cmd.find_renames = None
+        if (self.info.root_diff):
+            cmd.root = None
         # Note we intentionally do not use -z, as the filename is just for
         # reference, and it is safer to let git do the escaping.
 
diff --git a/sample.conf b/sample.conf
index 705a022..f5e950a 100644
--- a/sample.conf
+++ b/sample.conf
@@ -11,6 +11,15 @@ path = /srv/git/repo/
 # Useful to disable an expensive operation in very large repositories.
 #tree = yes
 
+# Show a "creation event" diff for a root commit? (optional)
+# For projects placed under revision control from inception, the root commit
+# diff is often meaningful. However, in cases when a well established, large
+# project is placed under revision control belatedly, the root commit may
+# represent a lump import of the entire project, in which case such a
+# "creation event" diff would likely be considered meaningless noise.
+# Default: yes
+#rootdiff = yes
+
 # How many commits to show in the summary page (optional).
 #commits_in_summary = 10