--- a/taskcluster/taskgraph/transforms/job/common.py
+++ b/taskcluster/taskgraph/transforms/job/common.py
@@ -127,16 +127,44 @@ def support_vcs_checkout(config, job, ta
     # for hg.mozilla.org.
     taskdesc['scopes'].append('secrets:get:project/taskcluster/gecko/hgfingerprint')
 
     # only some worker platforms have taskcluster-proxy enabled
     if job['worker']['implementation'] in ('docker-worker', 'docker-engine'):
         taskdesc['worker']['taskcluster-proxy'] = True
 
 
+def generic_worker_hg_commands(base_repo, head_repo, head_rev, path):
+    """Obtain commands needed to obtain a Mercurial checkout on generic-worker.
+
+    Returns two command strings. One performs the checkout. Another logs.
+    """
+    args = [
+        r'"c:\Program Files\Mercurial\hg.exe"',
+        'robustcheckout',
+        '--sharebase', r'y:\hg-shared',
+        '--purge',
+        '--upstream', base_repo,
+        '--revision', head_rev,
+        head_repo,
+        path,
+    ]
+
+    logging_args = [
+        b":: TinderboxPrint:<a href={source_repo}/rev/{revision} "
+        b"title='Built from {repo_name} revision {revision}'>{revision}</a>"
+        b"\n".format(
+            revision=head_rev,
+            source_repo=head_repo,
+            repo_name=head_repo.split('/')[-1]),
+    ]
+
+    return ' '.join(args), ' '.join(logging_args)
+
+
 def docker_worker_setup_secrets(config, job, taskdesc):
     """Set up access to secrets via taskcluster-proxy.  The value of
     run['secrets'] should be a boolean or a list of secret names that
     can be accessed."""
     if not job['run'].get('secrets'):
         return
 
     taskdesc['worker']['taskcluster-proxy'] = True

--- a/taskcluster/taskgraph/transforms/job/mozharness.py
+++ b/taskcluster/taskgraph/transforms/job/mozharness.py
@@ -19,16 +19,17 @@ from voluptuous import Required, Optiona
 from taskgraph.transforms.job import run_job_using
 from taskgraph.transforms.job.common import (
     docker_worker_add_workspace_cache,
     docker_worker_add_gecko_vcs_env_vars,
     docker_worker_setup_secrets,
     docker_worker_add_artifacts,
     docker_worker_add_tooltool,
     generic_worker_add_artifacts,
+    generic_worker_hg_commands,
     support_vcs_checkout,
 )
 
 mozharness_run_schema = Schema({
     Required('using'): 'mozharness',
 
     # the mozharness script used to run this task, relative to the testing/
     # directory and using forward slashes even on Windows
@@ -287,53 +288,30 @@ def mozharness_on_generic_worker(config,
 
     for option in run.get('options', []):
         assert ' ' not in option
         mh_command.append('--' + option)
     if run.get('custom-build-variant-cfg'):
         mh_command.append('--custom-build-variant')
         mh_command.append(run['custom-build-variant-cfg'])
 
-    def checkout_repo(base_repo, head_repo, head_rev, path):
-        hg_command = ['"c:\\Program Files\\Mercurial\\hg.exe"']
-        hg_command.append('robustcheckout')
-        hg_command.extend(['--sharebase', 'y:\\hg-shared'])
-        hg_command.append('--purge')
-        hg_command.extend(['--upstream', base_repo])
-        hg_command.extend(['--revision', head_rev])
-        hg_command.append(head_repo)
-        hg_command.append(path)
-
-        logging_command = [
-            b":: TinderboxPrint:<a href={source_repo}/rev/{revision} "
-            b"title='Built from {repo_name} revision {revision}'>{revision}</a>\n".format(
-                revision=head_rev,
-                source_repo=head_repo,
-                repo_name=head_repo.split('/')[-1],
-            )]
-
-        return [
-            ' '.join(hg_command),
-            ' '.join(logging_command),
-        ]
-
-    hg_commands = checkout_repo(
+    hg_commands = generic_worker_hg_commands(
         base_repo=env['GECKO_BASE_REPOSITORY'],
         head_repo=env['GECKO_HEAD_REPOSITORY'],
         head_rev=env['GECKO_HEAD_REV'],
-        path='.\\build\\src')
+        path=r'.\build\src',
+    )
 
     if run['comm-checkout']:
         hg_commands.extend(
-            checkout_repo(
+            generic_worker_hg_commands(
                 base_repo=env['COMM_BASE_REPOSITORY'],
                 head_repo=env['COMM_HEAD_REPOSITORY'],
                 head_rev=env['COMM_HEAD_REV'],
-                path='.\\build\\src\\comm')
-        )
+                path=r'.\build\src\comm'))
 
     worker['command'] = []
     if taskdesc.get('needs-sccache'):
         worker['command'].extend([
             # Make the comment part of the first command, as it will help users to
             # understand what is going on, and why these steps are implemented.
             dedent('''\
             :: sccache currently uses the full compiler commandline as input to the

--- a/taskcluster/taskgraph/transforms/job/spidermonkey.py
+++ b/taskcluster/taskgraph/transforms/job/spidermonkey.py
@@ -9,16 +9,17 @@ from __future__ import absolute_import, 
 
 from taskgraph.util.schema import Schema
 from voluptuous import Required, Any
 
 from taskgraph.transforms.job import run_job_using
 from taskgraph.transforms.job.common import (
     docker_worker_add_artifacts,
     generic_worker_add_artifacts,
+    generic_worker_hg_commands,
     docker_worker_add_gecko_vcs_env_vars,
     docker_worker_add_tooltool,
     support_vcs_checkout,
 )
 
 sm_run_schema = Schema({
     Required('using'): Any('spidermonkey', 'spidermonkey-package', 'spidermonkey-mozjs-crate',
                            'spidermonkey-rust-bindings'),
@@ -110,25 +111,22 @@ def generic_worker_spidermonkey(config, 
         script = "build-sm-mozjs-crate.sh"
         # Don't allow untested configurations yet
         raise Exception("spidermonkey-mozjs-crate is not a supported configuration")
     elif run['using'] == 'spidermonkey-rust-bindings':
         script = "build-sm-rust-bindings.sh"
         # Don't allow untested configurations yet
         raise Exception("spidermonkey-rust-bindings is not a supported configuration")
 
-    hg_command = ['"c:\\Program Files\\Mercurial\\hg.exe"']
-    hg_command.append('robustcheckout')
-    hg_command.extend(['--sharebase', 'y:\\hg-shared'])
-    hg_command.append('--purge')
-    hg_command.extend(['--upstream', 'https://hg.mozilla.org/mozilla-unified'])
-    hg_command.extend(['--revision', env['GECKO_HEAD_REV']])
-    hg_command.append(env['GECKO_HEAD_REPOSITORY'])
-    hg_command.append('.\\src')
+    hg_command = generic_worker_hg_commands(
+        'https://hg.mozilla.org/mozilla-unified',
+        env['GECKO_HEAD_REPOSITORY'],
+        env['GECKO_HEAD_REV'],
+        r'.\src',
+    )[0]
 
     command = ['c:\\mozilla-build\\msys\\bin\\bash.exe '  # string concat
                '"./src/taskcluster/scripts/builder/%s"' % script]
 
-    worker['command'] = []
-    worker['command'].extend([
-        ' '.join(hg_command),
-        ' '.join(command)
-    ])
+    worker['command'] = [
+        hg_command,
+        ' '.join(command),
+    ]

--- a/taskcluster/taskgraph/transforms/job/toolchain.py
+++ b/taskcluster/taskgraph/transforms/job/toolchain.py
@@ -12,16 +12,17 @@ from mozbuild.shellutil import quote as 
 from taskgraph.util.schema import Schema
 from voluptuous import Optional, Required, Any
 
 from taskgraph.transforms.job import run_job_using
 from taskgraph.transforms.job.common import (
     docker_worker_add_gecko_vcs_env_vars,
     docker_worker_add_artifacts,
     docker_worker_add_tooltool,
+    generic_worker_hg_commands,
     support_vcs_checkout,
 )
 from taskgraph.util.hash import hash_paths
 from taskgraph import GECKO
 from taskgraph.util.cached_tasks import add_optimization
 import taskgraph
 
 
@@ -200,37 +201,33 @@ def windows_toolchain(config, job, taskd
 
     env = worker['env']
     env.update({
         'MOZ_BUILD_DATE': config.params['moz_build_date'],
         'MOZ_SCM_LEVEL': config.params['level'],
         'MOZ_AUTOMATION': '1',
     })
 
-    hg = r'c:\Program Files\Mercurial\hg.exe'
-    hg_command = ['"{}"'.format(hg)]
-    hg_command.append('robustcheckout')
-    hg_command.extend(['--sharebase', 'y:\\hg-shared'])
-    hg_command.append('--purge')
-    hg_command.extend(['--upstream', 'https://hg.mozilla.org/mozilla-unified'])
-    hg_command.extend(['--revision', '%GECKO_HEAD_REV%'])
-    hg_command.append('%GECKO_HEAD_REPOSITORY%')
-    hg_command.append('.\\build\\src')
+    hg_command = generic_worker_hg_commands(
+        'https://hg.mozilla.org/mozilla-unified',
+        env['GECKO_HEAD_REPOSITORY'],
+        env['GECKO_HEAD_REV'],
+        r'.\build\src')[0]
 
     # Use `mach` to invoke python scripts so in-tree libraries are available.
     if run['script'].endswith('.py'):
         raise NotImplementedError("Python scripts don't work on Windows")
 
     args = run.get('arguments', '')
     if args:
         args = ' ' + shell_quote(*args)
 
     bash = r'c:\mozilla-build\msys\bin\bash'
     worker['command'] = [
-        ' '.join(hg_command),
+        hg_command,
         # do something intelligent.
         r'{} build/src/taskcluster/scripts/misc/{}{}'.format(
             bash, run['script'], args)
     ]
 
     attributes = taskdesc.setdefault('attributes', {})
     attributes['toolchain-artifact'] = run['toolchain-artifact']
     if 'toolchain-alias' in run: