devtools: replace github-merge with python version

This is meant to be a direct translation of the bash script,
with the difference that it retrieves the PR title from github,
thus creating pull messages like:

    Merge #12345: Expose transaction temperature over RPC

1 files changed, 223 insertions, 0 deletions

diff --git a/contrib/devtools/github-merge.py b/contrib/devtools/github-merge.py
new file mode 100755
index 0000000000..33d33b7005
--- /dev/null
+++ b/contrib/devtools/github-merge.py
@@ -0,0 +1,223 @@
+#!/usr/bin/env python2
+# Copyright (c) 2016 Bitcoin Core Developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+# This script will locally construct a merge commit for a pull request on a
+# github repository, inspect it, sign it and optionally push it.
+
+# The following temporary branches are created/overwritten and deleted:
+# * pull/$PULL/base (the current master we're merging onto)
+# * pull/$PULL/head (the current state of the remote pull request)
+# * pull/$PULL/merge (github's merge)
+# * pull/$PULL/local-merge (our merge)
+
+# In case of a clean merge that is accepted by the user, the local branch with
+# name $BRANCH is overwritten with the merged result, and optionally pushed.
+from __future__ import division,print_function,unicode_literals
+import os,sys
+from sys import stdin,stdout,stderr
+import argparse
+import subprocess
+
+# External tools (can be overridden using environment)
+GIT = os.getenv('GIT','git')
+BASH = os.getenv('BASH','bash')
+
+def git_config_get(option, default=None):
+    '''
+    Get named configuration option from git repository.
+    '''
+    try:
+        return subprocess.check_output([GIT,'config','--get',option]).rstrip()
+    except subprocess.CalledProcessError as e:
+        return default
+
+def retrieve_pr_title(repo,pull):
+    '''
+    Retrieve pull request title from github.
+    Return None if no title can be found, or an error happens.
+    '''
+    import urllib2,json
+    try:
+        req = urllib2.Request("https://api.github.com/repos/"+repo+"/pulls/"+pull)
+        result = urllib2.urlopen(req)
+        result = json.load(result)
+        return result['title']
+    except Exception as e:
+        print('Warning: unable to retrieve pull title from github: %s' % e)
+        return None
+
+def ask_prompt(text):
+    print(text,end=" ",file=stderr)
+    reply = stdin.readline().rstrip()
+    print("",file=stderr)
+    return reply
+
+def parse_arguments(branch):
+    epilog = '''
+        In addition, you can set the following git configuration variables:
+        githubmerge.repository (mandatory),
+        user.signingkey (mandatory),
+        githubmerge.host (default: git@github.com),
+        githubmerge.branch (default: master),
+        githubmerge.testcmd (default: none).
+    '''
+    parser = argparse.ArgumentParser(description='Utility to merge, sign and push github pull requests',
+            epilog=epilog)
+    parser.add_argument('pull', metavar='PULL', type=int, nargs=1,
+        help='Pull request ID to merge')
+    parser.add_argument('branch', metavar='BRANCH', type=str, nargs='?',
+        default=branch, help='Branch to merge against (default: '+branch+')')
+    return parser.parse_args()
+
+def main():
+    # Extract settings from git repo
+    repo = git_config_get('githubmerge.repository')
+    host = git_config_get('githubmerge.host','git@github.com')
+    branch = git_config_get('githubmerge.branch','master')
+    testcmd = git_config_get('githubmerge.testcmd')
+    signingkey = git_config_get('user.signingkey')
+    if repo is None:
+        print("ERROR: No repository configured. Use this command to set:", file=stderr)
+        print("git config githubmerge.repository <owner>/<repo>", file=stderr)
+        exit(1)
+    if signingkey is None:
+        print("ERROR: No GPG signing key set. Set one using:",file=stderr)
+        print("git config --global user.signingkey <key>",file=stderr)
+        exit(1)
+
+    host_repo = host+":"+repo # shortcut for push/pull target
+
+    # Extract settings from command line
+    args = parse_arguments(branch)
+    pull = str(args.pull[0])
+    branch = args.branch
+
+    # Initialize source branches
+    head_branch = 'pull/'+pull+'/head'
+    base_branch = 'pull/'+pull+'/base'
+    merge_branch = 'pull/'+pull+'/merge'
+    local_merge_branch = 'pull/'+pull+'/local-merge'
+
+    devnull = open(os.devnull,'w')
+    try:
+        subprocess.check_call([GIT,'checkout','-q',branch])
+    except subprocess.CalledProcessError as e:
+        print("ERROR: Cannot check out branch %s." % (branch), file=stderr)
+        exit(3)
+    try:
+        subprocess.check_call([GIT,'fetch','-q',host_repo,'+refs/pull/'+pull+'/*:refs/heads/pull/'+pull+'/*'])
+    except subprocess.CalledProcessError as e:
+        print("ERROR: Cannot find pull request #%s on %s." % (pull,host_repo), file=stderr)
+        exit(3)
+    try:
+        subprocess.check_call([GIT,'log','-q','-1','refs/heads/'+head_branch], stdout=devnull, stderr=stdout)
+    except subprocess.CalledProcessError as e:
+        print("ERROR: Cannot find head of pull request #%s on %s." % (pull,host_repo), file=stderr)
+        exit(3)
+    try:
+        subprocess.check_call([GIT,'log','-q','-1','refs/heads/'+merge_branch], stdout=devnull, stderr=stdout)
+    except subprocess.CalledProcessError as e:
+        print("ERROR: Cannot find merge of pull request #%s on %s." % (pull,host_repo), file=stderr)
+        exit(3)
+    try:
+        subprocess.check_call([GIT,'fetch','-q',host_repo,'+refs/heads/'+branch+':refs/heads/'+base_branch])
+    except subprocess.CalledProcessError as e:
+        print("ERROR: Cannot find branch %s on %s." % (branch,host_repo), file=stderr)
+        exit(3)
+    subprocess.check_call([GIT,'checkout','-q',base_branch])
+    subprocess.call([GIT,'branch','-q','-D',local_merge_branch], stderr=devnull)
+    subprocess.check_call([GIT,'checkout','-q','-b',local_merge_branch])
+
+    try:
+        # Create unsigned merge commit.
+        title = retrieve_pr_title(repo,pull)
+        if title:
+            firstline = 'Merge #%s: %s' % (pull,title)
+        else:
+            firstline = 'Merge #%s' % (pull,)
+        message = firstline + '\n\n'
+        message += subprocess.check_output([GIT,'log','--no-merges','--topo-order','--pretty=format:%h %s (%an)',base_branch+'..'+head_branch])
+        try:
+            subprocess.check_call([GIT,'merge','-q','--commit','--no-edit','--no-ff','-m',message,head_branch])
+        except subprocess.CalledProcessError as e:
+            print("ERROR: Cannot be merged cleanly.",file=stderr)
+            subprocess.check_call([GIT,'merge','--abort'])
+            exit(4)
+        logmsg = subprocess.check_output([GIT,'log','--pretty=format:%s','-n','1'])
+        if logmsg.rstrip() != firstline.rstrip():
+            print("ERROR: Creating merge failed (already merged?).",file=stderr)
+            exit(4)
+
+        # Run test command if configured.
+        if testcmd:
+            # Go up to the repository's root.
+            toplevel = subprocess.check_output([GIT,'rev-parse','--show-toplevel'])
+            os.chdir(toplevel)
+            if subprocess.call(testcmd,shell=True):
+                print("ERROR: Running %s failed." % testcmd,file=stderr)
+                exit(5)
+
+            # Show the created merge.
+            diff = subprocess.check_output([GIT,'diff',merge_branch+'..'+local_merge_branch])
+            subprocess.check_call([GIT,'diff',base_branch+'..'+local_merge_branch])
+            if diff:
+                print("WARNING: merge differs from github!",file=stderr)
+                reply = ask_prompt("Type 'ignore' to continue.")
+                if reply.lower() == 'ignore':
+                    print("Difference with github ignored.",file=stderr)
+                else:
+                    exit(6)
+            reply = ask_prompt("Press 'd' to accept the diff.")
+            if reply.lower() == 'd':
+                print("Diff accepted.",file=stderr)
+            else:
+                print("ERROR: Diff rejected.",file=stderr)
+                exit(6)
+        else:
+            # Verify the result manually.
+            print("Dropping you on a shell so you can try building/testing the merged source.",file=stderr)
+            print("Run 'git diff HEAD~' to show the changes being merged.",file=stderr)
+            print("Type 'exit' when done.",file=stderr)
+            if os.path.isfile('/etc/debian_version'): # Show pull number on Debian default prompt
+                os.putenv('debian_chroot',pull)
+            subprocess.call([BASH,'-i'])
+            reply = ask_prompt("Type 'm' to accept the merge.")
+            if reply.lower() == 'm':
+                print("Merge accepted.",file=stderr)
+            else:
+                print("ERROR: Merge rejected.",file=stderr)
+                exit(7)
+
+        # Sign the merge commit.
+        reply = ask_prompt("Type 's' to sign off on the merge.")
+        if reply == 's':
+            try:
+                subprocess.check_call([GIT,'commit','-q','--gpg-sign','--amend','--no-edit'])
+            except subprocess.CalledProcessError as e:
+                print("Error signing, exiting.",file=stderr)
+                exit(1)
+        else:
+            print("Not signing off on merge, exiting.",file=stderr)
+            exit(1)
+
+        # Put the result in branch.
+        subprocess.check_call([GIT,'checkout','-q',branch])
+        subprocess.check_call([GIT,'reset','-q','--hard',local_merge_branch])
+    finally:
+        # Clean up temporary branches.
+        subprocess.call([GIT,'checkout','-q',branch])
+        subprocess.call([GIT,'branch','-q','-D',head_branch],stderr=devnull)
+        subprocess.call([GIT,'branch','-q','-D',base_branch],stderr=devnull)
+        subprocess.call([GIT,'branch','-q','-D',merge_branch],stderr=devnull)
+        subprocess.call([GIT,'branch','-q','-D',local_merge_branch],stderr=devnull)
+
+    # Push the result.
+    reply = ask_prompt("Type 'push' to push the result to %s, branch %s." % (host_repo,branch))
+    if reply.lower() == 'push':
+        subprocess.check_call([GIT,'push',host_repo,'refs/heads/'+branch])
+
+if __name__ == '__main__':
+    main()
+