Document/usage/dogfood test update after merge for issue #4 (Revision control support); more robust on parsing strange diff

Makefile

 .PHONY: dogfood test $(TESTS)
 
 dogfood:
+	src/cdiff.py -s
 	git diff | src/cdiff.py
 	git diff | src/cdiff.py -s
 

README.md

 
 ## Usage
 
-Just give it a diff (patch) file or pipe a diff to it.  Use option `-s` for
-side-by-side view, and option `-w N` to set a text width other than default
-`80`.  See examples below
+Cdiff reads diff from diff (patch) file if given, or stdin if redirected, or
+diff produced by revision tool if in a git/svn/hg workspace.  Use option `-s`
+to enable side by side view, and option `-w N` to set a text width other than
+default `80`.  See examples below.
+
+Show usage:
+
+    cdiff -h
 
 View a diff (patch) file:
 
     cdiff foo.patch -s          # view in side by side mode
     cdiff foo.patch -s -w 90    # use text width 90 other than default 80
 
-Read diff from svn, git, or hg:
+Read diff from local modification in a svn, git, or hg workspace:
 
+    cd proj-workspace
     cdiff
     cdiff -s
     cdiff -s -w 90
 
-Read diffs in git logs:
+Pipe in a diff:
 
+    svn diff -r PREV | cdiff -s
     git log -p -2 | cdiff -s
     git show <commit> | cdiff -s
 

src/cdiff.py

 import sys
 
 if sys.hexversion < 0x02050000:
-    sys.stderr.write("ERROR: requires python >= 2.5.0\n")
+    sys.stderr.write("*** Requires python >= 2.5.0\n")
     sys.exit(1)
 IS_PY3 = sys.hexversion >= 0x03000000
 
                     # @@ -3,7 +3,6 @@
                     hunk_header = stream.pop(0)
                     a = hunk_header.split()[1].split(',')   # -3 7
-                    old_addr = (int(a[0][1:]), int(a[1]))
+                    if len(a) > 1:
+                        old_addr = (int(a[0][1:]), int(a[1]))
+                    else:
+                        # @@ -1 +1,2 @@
+                        old_addr = (int(a[0][1:]), 0)
+
                     b = hunk_header.split()[2].split(',')   # +3 6
                     if len(b) > 1:
                         new_addr = (int(b[0][1:]), int(b[1]))
 if __name__ == '__main__':
     import optparse
 
-    usage = '''%s [options] [diff]''' % os.path.basename(sys.argv[0])
-    description= ('''View incremental, colored diff in unified format or '''
-                  '''in side by side mode with auto pager, read stdin if '''
-                  '''diff (patch) file is not given''')
+    supported_vcs = [check[0] for check, _ in REVISION_CONTROL]
+
+    usage = '%s [options] [diff]' % os.path.basename(sys.argv[0])
+    description= ('View incremental, colored diff in unified format or '
+                  'side by side with auto pager.  Read diff from diff '
+                  '(patch) file if given, or stdin if redirected, or '
+                  'diff produced by revision tool if in a %s workspace') \
+            % '/'.join(supported_vcs)
 
     parser = optparse.OptionParser(usage=usage, description=description)
     parser.add_option('-s', '--side-by-side', action='store_true',
     elif sys.stdin.isatty():
         diff_hdl = revision_control_diff()
         if not diff_hdl:
+            sys.stderr.write(('*** Not in a supported workspace, supported '
+                              'are: %s\n\n') % ', '.join(supported_vcs))
             parser.print_help()
             sys.exit(1)
     else:

tests/strange.diff

 +++ b/.gitignore
 @@ -0,0 +1 @@
 +*.pyc
+diff --git a/README b/README
+index 7e70850..b5eb369 100644
+--- a/README
++++ b/README
+@@ -1 +1,2 @@
+ Sun Feb  3 13:57:05 CST 2013
++Sun Feb  3 13:57:15 CST 2013