contrib/debugcmdserver.py

hgweb: allow viewing diffs against p1 or p2 for merge commits (issue3904)

This adds UI portion of the feature that has resided in mercurial since 2012.
Back then the interface was added together with the code, but was shortly
backed out because it was deemed "not ready". Code, however, stayed.

For the original feature and its implementation, see issue2810 and
d605a82cf189.

In short, the backed-out interface had two outstanding issues:
1. it was introducing an entirely new term (baseline) and
2. it was present on every changeset's page, even for changesets with 1 parent
   (or no parents), which didn't make sense

This patch implements a hopefully better interface because:
1. it uses the usual terms (diff) and
2. it only shows up when there actually are 2 parents.

#!/usr/bin/env python
#
# Dumps output generated by Mercurial's command server in a formatted style to a
# given file or stderr if '-' is specified. Output is also written in its raw
# format to stdout.
#
# $ ./hg serve --cmds pipe | ./contrib/debugcmdserver.py -
# o, 52   -> 'capabilities: getencoding runcommand\nencoding: UTF-8'

import sys, struct

if len(sys.argv) != 2:
    print 'usage: debugcmdserver.py FILE'
    sys.exit(1)

outputfmt = '>cI'
outputfmtsize = struct.calcsize(outputfmt)

if sys.argv[1] == '-':
    log = sys.stderr
else:
    log = open(sys.argv[1], 'a')

def read(size):
    data = sys.stdin.read(size)
    if not data:
        raise EOFError
    sys.stdout.write(data)
    sys.stdout.flush()
    return data

try:
    while True:
        header = read(outputfmtsize)
        channel, length = struct.unpack(outputfmt, header)
        log.write('%s, %-4d' % (channel, length))
        if channel in 'IL':
            log.write(' -> waiting for input\n')
        else:
            data = read(length)
            log.write(' -> %r\n' % data)
        log.flush()
except EOFError:
    pass
finally:
    if log != sys.stderr:
        log.close()