Git has an unfortunate habit of detaching heads every time you change branches on the top level repo. This script goes through all the submodules and looks for a commit on a branch that matches the current hash of that branch. If it finds it it does a checkout on the branch. NOTE: this isn't foolproof, if there are multiple branches with the sam…

fixDetachedHeads.py

#!/usr/bin/env python

import platform
import os
import sys
import io
import subprocess

BASE_DIR = os.getcwd()
print("" + BASE_DIR)
DEBUG_OUTPUT = False

def log(string):
    print("--- " + string)

def errorLog(string):
    print("--- ERROR " + string)

def dlog(string):
    if DEBUG_OUTPUT:
        print("*** " + string)


def findToolCommand(command, paths_to_search, required = False):
    command_res = command
    found = False

    for path in paths_to_search:
        command_abs = os.path.join(path, command)
        if os.path.exists(command_abs):
            command_res = command_abs
            found = True
            break;

    if required and not found:
        log("WARNING: command " + command + " not found, but required by script")

    dlog("Found '" + command + "' as " + command_res)
    return command_res

# execute command but return status of command as an integer
def executeCommand(command, printCommand = False, quiet = False):

    printCommand = printCommand or DEBUG_OUTPUT
    out = None
    err = None

    if quiet:
        out = open(os.devnull, 'w')
        err = subprocess.STDOUT

    if printCommand:
        if DEBUG_OUTPUT:
            dlog(">>> " + command)
        else:
            log(">>> " + command)

    return subprocess.call(command, shell = True, stdout=out, stderr=err);

# Execute command but return output as text
def executeCommandWithOutput(command, printCommand = False, quiet = False):

    printCommand = printCommand or DEBUG_OUTPUT
    out = None
    err = None

    if quiet:
        out = open(os.devnull, 'w')
        err = subprocess.STDOUT

    if printCommand:
        if DEBUG_OUTPUT:
            dlog(">>> " + command)
        else:
            log(">>> " + command)

    return os.popen(command).read()

def dieIfNonZero(res):
    if res != 0:
        raise ValueError("Command returned non-zero status.");

# Returns a list of dictionaries whhere each item is a submodule 
def getHeadsOfSubmodulesIncludingGodRepo():
    submoduleRecords = [];
    output = executeCommandWithOutput(TOOL_COMMAND_GIT + " submodule");
    if (len(output) == 0):
        errorLog("No submodule results found");
        return;

    mainBranchHash = executeCommandWithOutput(TOOL_COMMAND_GIT + " rev-parse HEAD").strip()
        
    submoduleRecords.append({"hash": mainBranchHash, "path": "."});

    submoduleRecord = output.split('\n');
    for submodule in submoduleRecord:
        submoduleText = submodule.strip();
        if (len(submoduleText) == 0):
            continue;
        recordDetails = submodule.strip().split(' ');
        dlog ("submodule hash " + recordDetails[0] + ", path: " + recordDetails[1]);
        submoduleRecords.append({"hash":recordDetails[0], "path":recordDetails[1]});
    return submoduleRecords;

def getHeadsOfCurrentBranches():
    branchRecords = [];
    output = executeCommandWithOutput(TOOL_COMMAND_GIT + " for-each-ref --sort=-committerdate refs/heads/ --format='%(objectname) %(refname:short)'").strip();
    if (len(output) == 0):
        errorLog("No branch results found");
        return;

    branchRecord = output.split('\n');
    for branch in branchRecord:
        branchText = branch.strip();
        if (len(branchText) == 0):
            continue;
        branchDetails = branchText.strip().split(' ');
        dlog ("branch name " + branchDetails[1] + ", hash: " + branchDetails[0]);
        branchRecords.append({"hash":branchDetails[0], "name":branchDetails[1]});
    return branchRecords;

log("Fixing Detached Heads in " + BASE_DIR);

paths_to_search = os.environ["PATH"].split(":") + ["/usr/local/bin", "/opt/local/bin", "/usr/bin"]
TOOL_COMMAND_GIT = findToolCommand("git", paths_to_search, required = True)

# get all repos
repos = getHeadsOfSubmodulesIncludingGodRepo();

mainRepoBranchName = "";

# update repos first
executeCommand(TOOL_COMMAND_GIT + " submodule update --recursive")

# Go through all repos, check the current hash of the branch
# If we detect it is a DETACHED HEAD then we check all branches
# If we find a branch whose tip commit matches what we're at then perform a git command
for repo in repos:
    os.chdir(os.path.join(BASE_DIR, repo["path"]));
    currentHead = executeCommandWithOutput(TOOL_COMMAND_GIT + " rev-parse --symbolic-full-name --abbrev-ref HEAD").strip()
    repoName = repo["path"];
    if (repoName == "."):
        repoName = "God-Repo";

    log ("==============================================");
    log ("Repo: " + repoName);
    log ("Hash: '" + repo["hash"] + "'");
    log ("Current head: '" + currentHead + "'");
    
    # Is it a detached head?
    if currentHead == "HEAD":
        branchRecords = getHeadsOfCurrentBranches();
        currentHeadCommitHash = executeCommandWithOutput(TOOL_COMMAND_GIT + " rev-parse HEAD").strip()
        branchName = "";
        branchHash = "";
        for branch in branchRecords:
            log ("checking branch '" + branch["name"] + "', hash: " + branch["hash"]);
            if branch["hash"] == currentHeadCommitHash:
                if (branchName == mainRepoBranchName or len(branchName) == 0):
                    branchName = branch["name"];
                    branchHash = branch["hash"];
        if len(branchName) > 0 and len(branchHash) > 0:
            log("Found match for current hash in branch: " + branchName);
            # NOTE: pulled out sourcetree specifics so the user interface updates correctly
            dieIfNonZero(executeCommand(TOOL_COMMAND_GIT + " -c diff.mnemonicprefix=false -c core.quotepath=false -c credential.helper=sourcetree checkout " + branchName));
        else:
            log ("HEAD DETACHED - Did not find a commit on any branch tip for hash " + currentHeadCommitHash);
    else:
        log("Repo - HEAD is not detached");
        mainRepoBranchName = currentHead;

    log ("==============================================");
    log("")

os.chdir(BASE_DIR);